AP Chemistry Quiz: Galvanic Voltaic And Electrolytic Cells
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Galvanic Voltaic And Electrolytic CellsQuestion 1 of 20

A student sets up two half-cells connected by a salt bridge and a wire: Fe(s) in FeSO4_4(aq) and Ag(s) in AgNO3_3(aq). The student measures a steady voltage with a voltmeter (no battery attached). When the wire is connected through a small motor, the motor turns briefly and the Ag electrode increases in mass. Which statement correctly classifies the process and identifies a defining feature?

It is an electrolytic process, and it requires an external power source to force a nonspontaneous reaction.
It is a galvanic (voltaic) process, and it requires an external power source to force a nonspontaneous reaction.
It is a galvanic (voltaic) process, and it produces electrical energy from a spontaneous redox reaction.
It is an electrolytic process, and it produces electrical energy from a spontaneous redox reaction.
It is a galvanic (voltaic) process, and it operates only because the salt bridge supplies electrons to the circuit.
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AP Chemistry Quiz

AP Chemistry Quiz: Galvanic Voltaic And Electrolytic Cells

Practice Galvanic Voltaic And Electrolytic Cells in AP Chemistry with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Galvanic Voltaic And Electrolytic Cells, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Chemistry.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

A student sets up two half-cells connected by a salt bridge and a wire: Fe(s) in FeSO4_4(aq) and Ag(s) in AgNO3_3(aq). The student measures a steady voltage with a voltmeter (no battery attached). When the wire is connected through a small motor, the motor turns briefly and the Ag electrode increases in mass. Which statement correctly classifies the process and identifies a defining feature?

  1. It is an electrolytic process, and it requires an external power source to force a nonspontaneous reaction.
  2. It is a galvanic (voltaic) process, and it requires an external power source to force a nonspontaneous reaction.
  3. It is a galvanic (voltaic) process, and it produces electrical energy from a spontaneous redox reaction. (correct answer)
  4. It is an electrolytic process, and it produces electrical energy from a spontaneous redox reaction.
  5. It is a galvanic (voltaic) process, and it operates only because the salt bridge supplies electrons to the circuit.

Explanation: This question tests your understanding of galvanic (voltaic) and electrolytic cells. In galvanic cells, spontaneous redox processes release free energy, which is harnessed as electrical work, such as powering a motor or generating voltage. Electrolytic cells demand input of electrical energy to drive nonspontaneous reactions, like electrolysis. The direction of electron flow is determined by spontaneity: in galvanic cells, electrons move naturally toward the more positive potential, while in electrolytic cells, an external force dictates the flow. A tempting distractor is choice A, which wrongly labels it as electrolytic, based on the misconception that mass changes at electrodes always indicate a forced process. To distinguish between cell types, remember that if electrical energy is produced, the cell is galvanic; if it must be supplied, the cell is electrolytic.

Question 2

A corrosion scientist demonstrates a simple cell by placing an iron nail and a copper strip into a saltwater-soaked paper towel so they are electrically connected through a wire. A small voltage is detected and the iron shows signs of oxidation over time without any external power source. Which statement correctly classifies the process and its defining feature?

  1. Electrolytic cell; a spontaneous redox reaction produces electrical energy in the external circuit
  2. Galvanic (voltaic) cell; a spontaneous redox reaction produces electrical energy in the external circuit (correct answer)
  3. Galvanic (voltaic) cell; an external power source is required to force electron flow
  4. Electrolytic cell; an external power source is required to force a nonspontaneous redox reaction
  5. Galvanic (voltaic) cell; the electrolyte provides electrons to the wire

Explanation: This question tests your understanding of galvanic (voltaic) and electrolytic cells. Galvanic cells produce energy via spontaneous redox, electrons flowing naturally. Electrolytic cells force nonspontaneous reactions with external power, directing electrons. Spontaneity and energy flow differentiate, affecting electron movement. Choice B is distractor, labeling electrolytic with spontaneity, assuming oxidation signs mean spontaneous without power. To distinguish between cell types, remember: if electrical energy is produced, the cell is galvanic; if it must be supplied, the cell is electrolytic.

Question 3

A student connects two half-cells with a salt bridge: Cu(s) in CuSO4_4(aq) and Ag(s) in AgNO3_3(aq). Without any external power source, electrons flow through the wire from the Cu electrode toward the Ag electrode, and the Ag electrode gains mass. Which statement correctly classifies the cell and its defining feature?

  1. Electrolytic cell; an external power source is required to force a nonspontaneous redox reaction
  2. Galvanic (voltaic) cell; a spontaneous redox reaction produces electrical energy in the external circuit (correct answer)
  3. Galvanic (voltaic) cell; the salt bridge supplies electrons to keep the reaction running
  4. Electrolytic cell; a spontaneous redox reaction produces electrical energy in the external circuit
  5. Electrolytic cell; the salt bridge is the power source that drives electron flow

Explanation: This question tests your understanding of galvanic (voltaic) and electrolytic cells. Galvanic cells generate electricity from spontaneous reactions, electrons moving naturally. Electrolytic cells require external power for nonspontaneous reactions, controlling electron flow. Spontaneity and energy distinguish types, determining electron movement. Choice A is distractor, calling it electrolytic needing power, assuming mass gain requires force despite spontaneity. To distinguish between cell types, remember: if electrical energy is produced, the cell is galvanic; if it must be supplied, the cell is electrolytic.

Question 4

A student connects two electrodes in an aqueous solution to a DC power supply. The student notes that one electrode becomes coated with a metal that was previously present only as ions in solution, and the other electrode shows signs of dissolution or gas formation. Which statement correctly classifies the process and its defining feature?

  1. Galvanic (voltaic) cell; a spontaneous redox reaction produces electrical energy in the external circuit
  2. Electrolytic cell; an external power source is required to force a nonspontaneous redox reaction (correct answer)
  3. Galvanic (voltaic) cell; an external power source is required to force a nonspontaneous redox reaction
  4. Electrolytic cell; a spontaneous redox reaction produces electrical energy in the external circuit
  5. Electrolytic cell; the electrolyte is the power source that drives electron flow

Explanation: This question tests your understanding of galvanic (voltaic) and electrolytic cells. In galvanic cells, spontaneous reactions yield electricity, electrons flowing spontaneously. Electrolytic cells need input for nonspontaneous reactions, forcing electron direction. Energy flow and spontaneity differentiate, governing movement. Choice A is incorrect, labeling galvanic with spontaneity, assuming metal coating means spontaneous without power. To distinguish between cell types, remember: if electrical energy is produced, the cell is galvanic; if it must be supplied, the cell is electrolytic.

Question 5

A student connects an Fe(s) electrode in FeSO4_4(aq) to a Ag(s) electrode in AgNO3_3(aq) using a salt bridge and a wire. A voltmeter connected across the electrodes reads a steady nonzero voltage without any battery attached. Over time, Ag(s) mass increases and the Fe(s) electrode loses mass. Which statement correctly classifies the process and identifies a defining feature?​

  1. It is an electrolytic cell because the voltmeter reading shows that electrical energy is being consumed to drive the reaction.
  2. It is a galvanic (voltaic) cell because the reaction occurs spontaneously and generates electrical energy (a measurable voltage) without an external power source. (correct answer)
  3. It is a galvanic (voltaic) cell because the salt bridge acts as the power source for electron flow.
  4. It is an electrolytic cell because electrons flow through the salt bridge from one solution to the other.
  5. It is an electrolytic cell because deposition of Ag(s) at an electrode requires external electrical energy.

Explanation: This question tests understanding of galvanic (voltaic) and electrolytic cells. The voltmeter reads a nonzero voltage without any battery attached, which proves the cell is spontaneously generating electrical energy from the redox reaction between Fe and Ag⁺. In this galvanic cell, Fe oxidizes (Fe → Fe²⁺ + 2e⁻) at the anode while Ag⁺ is reduced (Ag⁺ + e⁻ → Ag) at the cathode, with electrons flowing through the external wire. Choice A incorrectly claims that a voltmeter reading shows energy consumption, but voltmeters measure potential difference without consuming significant energy. The key strategy is that if a cell generates measurable voltage without external power, it must be galvanic.

Question 6

An object is electroplated with nickel by placing it in a NiSO4_4(aq) solution. The object is connected to the negative terminal of a power supply, a Ni(s) strip is connected to the positive terminal, and a visible Ni coating forms on the object only while the power supply is on. Which statement correctly classifies the process and identifies a defining feature?

  1. It is an electrolytic process, and it produces electrical energy from a spontaneous redox reaction.
  2. It is a galvanic (voltaic) process, and it requires an external power source to force a nonspontaneous reaction.
  3. It is a galvanic (voltaic) process, and it produces electrical energy from a spontaneous redox reaction.
  4. It is an electrolytic process, and it requires an external power source to force a nonspontaneous reaction. (correct answer)
  5. It is a galvanic (voltaic) process, and it operates only because the salt bridge supplies electrons to the circuit.

Explanation: This question tests your understanding of galvanic (voltaic) and electrolytic cells. Galvanic cells produce electrical energy from spontaneous reactions, with the cell potential being positive and no external input required. Electrolytic cells consume electrical energy to enable nonspontaneous reactions, often used in processes like plating or purification. Electron flow in galvanic cells is spontaneous from the oxidation to reduction site, but in electrolytic cells, it's imposed by the power source to reverse the natural tendency. A tempting distractor is choice B, which incorrectly identifies it as galvanic, arising from the misconception that metal deposition always results from a spontaneous reaction. To distinguish between cell types, remember that if electrical energy is produced, the cell is galvanic; if it must be supplied, the cell is electrolytic.

Question 7

A diagram shows a cell with Mg(s) in Mg(NO3_3)2_2(aq) on the left and Cu(s) in Cu(NO3_3)2_2(aq) on the right, connected by a salt bridge and an external wire. The arrow on the wire indicates electrons flow from the Mg electrode to the Cu electrode, and a voltmeter connected across the electrodes reads a positive voltage without any external power source. Which statement correctly classifies the process and identifies a defining feature?

  1. It is an electrolytic process, and it requires an external power source to force a nonspontaneous reaction.
  2. It is a galvanic (voltaic) process, and it produces electrical energy from a spontaneous redox reaction. (correct answer)
  3. It is an electrolytic process, and it produces electrical energy from a spontaneous redox reaction.
  4. It is a galvanic (voltaic) process, and it requires an external power source to force a nonspontaneous reaction.
  5. It is a galvanic (voltaic) process, and it operates only because the salt bridge supplies electrons to the circuit.

Explanation: This question tests your understanding of galvanic (voltaic) and electrolytic cells. Galvanic cells rely on spontaneous redox reactions to generate electricity, evident from a positive voltage reading without external aid. Electrolytic cells need an external power source to push nonspontaneous reactions forward, consuming energy in the process. The electron movement is spontaneous in galvanic cells, directed by the reaction's thermodynamics, whereas in electrolytic cells, it's driven against the gradient by the applied voltage. A tempting distractor is choice A, which misclassifies it as electrolytic, based on the misconception that electron flow direction alone determines nonspontaneity. To distinguish between cell types, remember that if electrical energy is produced, the cell is galvanic; if it must be supplied, the cell is electrolytic.

Question 8

A student observes that in an electrochemical cell, the reaction proceeds on its own once the circuit is closed, and the device can be used as a power source for a small calculator. No external battery is connected. Which statement correctly classifies the cell and its defining feature?

  1. Galvanic (voltaic) cell; an external power source is required to force a nonspontaneous redox reaction
  2. Galvanic (voltaic) cell; a spontaneous redox reaction produces electrical energy in the external circuit (correct answer)
  3. Galvanic (voltaic) cell; the salt bridge supplies electrons to keep the reaction running
  4. Electrolytic cell; a spontaneous redox reaction produces electrical energy in the external circuit
  5. Electrolytic cell; an external power source is required to force a nonspontaneous redox reaction

Explanation: This question tests your understanding of galvanic (voltaic) and electrolytic cells. Galvanic cells convert spontaneous redox to electrical energy, electrons moving naturally. Electrolytic cells force nonspontaneous redox with external energy, controlling path. This distinction affects classification and electron behavior. Choice B is tempting, labeling electrolytic with spontaneity, assuming powering devices means electrolytic. To distinguish between cell types, remember: if electrical energy is produced, the cell is galvanic; if it must be supplied, the cell is electrolytic.

Question 9

In a laboratory demonstration, a student connects a galvanic cell to a second electrochemical cell using wires. The galvanic cell powers the second cell, causing metal to plate onto an electrode in the second cell. No wall outlet or battery is used. Which statement best describes the second cell while it is being powered by the first?

  1. Electrolytic cell; a spontaneous redox reaction produces electrical energy in the external circuit
  2. Galvanic (voltaic) cell; a spontaneous redox reaction produces electrical energy in the external circuit
  3. Electrolytic cell; an external source of electrical energy is required to force a nonspontaneous redox reaction (correct answer)
  4. Electrolytic cell; the salt bridge supplies electrons to keep the reaction running
  5. Galvanic (voltaic) cell; an external power source is required to force a nonspontaneous redox reaction

Explanation: This question tests your understanding of galvanic (voltaic) and electrolytic cells. Galvanic cells harness spontaneous reactions to output electricity, electrons flowing voluntarily. Electrolytic cells input electricity to drive nonspontaneous reactions, compelling flow. This energy-spontaneity dynamic defines cell type and electron movement. Choice A is tempting, labeling galvanic with spontaneity, based on misconception that powering another cell makes the second spontaneous. To distinguish between cell types, remember: if electrical energy is produced, the cell is galvanic; if it must be supplied, the cell is electrolytic.

Question 10

A commercial alkaline battery powers a flashlight. As the battery discharges, chemical reactants inside the sealed cell are consumed and electrical energy is delivered to the circuit without any external power supply. Which statement correctly classifies the process and its defining feature?

  1. Electrolytic cell; a spontaneous redox reaction produces electrical energy in the external circuit
  2. Galvanic (voltaic) cell; an external power source is required to force electron flow
  3. Electrolytic cell; an external power source is required to force a nonspontaneous redox reaction
  4. Galvanic (voltaic) cell; the salt bridge supplies electrons to keep the reaction running
  5. Galvanic (voltaic) cell; a spontaneous redox reaction produces electrical energy in the external circuit (correct answer)

Explanation: This question tests your understanding of galvanic (voltaic) and electrolytic cells. Galvanic cells utilize spontaneous redox reactions to generate electrical energy, with electrons flowing freely from anode to cathode. Electrolytic cells demand an external power source to propel nonspontaneous reactions, reversing the natural electron flow. The interplay of spontaneity and energy flow differentiates the cells, determining if electrons move voluntarily or under compulsion. Choice D is an incorrect choice, classifying it as electrolytic with spontaneous energy production, stemming from the misconception that sealed systems like batteries must always require external power even when discharging spontaneously. To distinguish between cell types, remember: if electrical energy is produced, the cell is galvanic; if it must be supplied, the cell is electrolytic.

Question 11

An object is electroplated with nickel by placing it in a NiSO4_4(aq) solution and connecting it to the negative terminal of a DC power supply. A Ni(s) strip is connected to the positive terminal. Nickel metal builds up on the object only while the power supply is on. Which statement correctly classifies the process and its defining feature?

  1. Electrolytic cell; an external power source is required to force a nonspontaneous redox reaction (correct answer)
  2. Galvanic (voltaic) cell; a spontaneous redox reaction produces electrical energy in the external circuit
  3. Electrolytic cell; a spontaneous redox reaction produces electrical energy in the external circuit
  4. Galvanic (voltaic) cell; an external power source is required to force a nonspontaneous redox reaction
  5. Electrolytic cell; the salt bridge supplies electrons to keep the reaction running

Explanation: This question tests your understanding of galvanic (voltaic) and electrolytic cells. Galvanic cells feature spontaneous redox processes that produce electrical energy, with electrons flowing naturally due to a favorable potential difference. Electrolytic cells, on the other hand, use an external power source to drive nonspontaneous reactions, compelling electron movement against the potential gradient. The core distinction lies in whether the reaction's spontaneity allows energy release or necessitates energy input, which governs the electron flow direction. Choice B is a misleading option, incorrectly identifying it as galvanic with spontaneous energy production, based on the misconception that metal deposition always indicates a spontaneous process without considering the need for external power. To distinguish between cell types, remember: if electrical energy is produced, the cell is galvanic; if it must be supplied, the cell is electrolytic.

Question 12

Two half-cells are connected with a salt bridge: Sn(s) in SnCl2_2(aq) and Pb(s) in Pb(NO3_3)2_2(aq). A student connects the electrodes through a wire and observes that the voltmeter reads approximately 0 V and no sustained current flows unless a battery is connected in series. With the battery connected, the Pb electrode gains mass. Which statement best describes the process occurring when the battery is connected?

  1. Galvanic (voltaic) cell; a spontaneous redox reaction produces electrical energy in the external circuit
  2. Electrolytic cell; an external power source is required to force a nonspontaneous redox reaction (correct answer)
  3. Galvanic (voltaic) cell; an external power source is required to force a nonspontaneous redox reaction
  4. Electrolytic cell; a spontaneous redox reaction produces electrical energy in the external circuit
  5. Galvanic (voltaic) cell; the salt bridge supplies electrons to keep the reaction running

Explanation: This question tests your understanding of galvanic (voltaic) and electrolytic cells. Galvanic cells operate via spontaneous redox reactions that yield electrical energy, enabling electron flow without external intervention. In electrolytic cells, nonspontaneous reactions are forced by supplying electrical energy, directing electrons to achieve the desired chemical change. Spontaneity determines if the cell outputs energy (galvanic) or requires input (electrolytic), thus controlling the electron movement pathway. Choice A is a tempting distractor, labeling it as galvanic with spontaneous energy production, rooted in the misconception that near-zero voltage always means a spontaneous cell when in fact it indicates nonspontaneity here. To distinguish between cell types, remember: if electrical energy is produced, the cell is galvanic; if it must be supplied, the cell is electrolytic.

Question 13

A student attempts to deposit Cr(s) onto a metal key by placing the key in a solution containing Cr3+^{3+}(aq) and connecting the key to a DC power supply. The key becomes coated only while the power supply is on, and the coating process stops immediately when the power supply is removed. Which statement correctly classifies the process and its defining feature?

  1. Galvanic (voltaic) cell; the salt bridge supplies electrons to keep the reaction running
  2. Electrolytic cell; a spontaneous redox reaction produces electrical energy in the external circuit
  3. Galvanic (voltaic) cell; an external power source is required to force a nonspontaneous redox reaction
  4. Electrolytic cell; an external power source is required to force a nonspontaneous redox reaction (correct answer)
  5. Galvanic (voltaic) cell; a spontaneous redox reaction produces electrical energy in the external circuit

Explanation: This question tests your understanding of galvanic (voltaic) and electrolytic cells. In galvanic cells, spontaneous reactions yield electrical energy, electrons flowing spontaneously. Electrolytic cells need external energy for nonspontaneous reactions, driving electron flow. This difference in spontaneity and energy governs cell classification and electron behavior. Choice B is misleading, identifying it as galvanic with spontaneous energy, based on the misconception that coating processes are always spontaneous without external input. To distinguish between cell types, remember: if electrical energy is produced, the cell is galvanic; if it must be supplied, the cell is electrolytic.

Question 14

Water is electrolyzed in a Hoffman apparatus containing acidified water. Two inert electrodes are connected to a power supply, and gases collect in separate tubes only while the power supply is operating. Which statement correctly classifies the process and its defining feature?

  1. Electrolytic cell; the salt bridge supplies electrons to keep the reaction running
  2. Electrolytic cell; a spontaneous redox reaction produces electrical energy in the external circuit
  3. Galvanic (voltaic) cell; a spontaneous redox reaction produces electrical energy in the external circuit
  4. Galvanic (voltaic) cell; an external power source is required to force electron flow
  5. Electrolytic cell; an external power source is required to force a nonspontaneous redox reaction (correct answer)

Explanation: This question tests your understanding of galvanic (voltaic) and electrolytic cells. Galvanic cells produce energy from spontaneous reactions, electrons flowing voluntarily. Electrolytic cells consume energy for nonspontaneous reactions, forcing electron flow. Energy flow and spontaneity define cell type and electron direction. Choice A is incorrect, labeling it galvanic with spontaneity, assuming gas collection means spontaneous without power need. To distinguish between cell types, remember: if electrical energy is produced, the cell is galvanic; if it must be supplied, the cell is electrolytic.

Question 15

A table summarizes observations for a cell made from two half-cells connected by a salt bridge and an external wire.

Observations: (1) A voltmeter reads a steady positive voltage when connected across the electrodes; (2) no battery is connected; (3) one metal electrode slowly dissolves, and a different metal electrode gains mass.

Which statement correctly classifies the process and identifies a defining feature?

  1. It is a galvanic (voltaic) process, and it requires an external power source to force a nonspontaneous reaction.
  2. It is an electrolytic process, and it produces electrical energy from a spontaneous redox reaction.
  3. It is a galvanic (voltaic) process, and it operates only because the salt bridge supplies electrons to the circuit.
  4. It is a galvanic (voltaic) process, and it produces electrical energy from a spontaneous redox reaction. (correct answer)
  5. It is an electrolytic process, and it requires an external power source to force a nonspontaneous reaction.

Explanation: This question tests your understanding of galvanic (voltaic) and electrolytic cells. Galvanic cells produce electricity from spontaneous redox reactions, as indicated by positive voltage and mass transfers without external power. Electrolytic cells need external energy to drive nonspontaneous processes, lacking inherent voltage. The energy flow determines electron movement: spontaneous release in galvanic cells propels electrons, while input in electrolytic cells forces them. A tempting distractor is choice A, which incorrectly deems it electrolytic, based on the misconception that electrode dissolution always requires external forcing. To distinguish between cell types, remember that if electrical energy is produced, the cell is galvanic; if it must be supplied, the cell is electrolytic.

Question 16

Molten NaCl is placed in a container with two inert electrodes connected to a DC power supply. When the power supply is turned on, bubbles form at one electrode and a silvery metal forms at the other. The process stops when the power supply is disconnected. Which statement correctly classifies the process and its defining feature?

  1. Galvanic (voltaic) cell; a spontaneous redox reaction produces electrical energy in the external circuit
  2. Electrolytic cell; an external power source is required to force a nonspontaneous redox reaction (correct answer)
  3. Galvanic (voltaic) cell; an external power source is required to force a nonspontaneous redox reaction
  4. Electrolytic cell; a spontaneous redox reaction produces electrical energy in the external circuit
  5. Electrolytic cell; the salt bridge supplies electrons to keep the reaction running

Explanation: This question tests your understanding of galvanic (voltaic) and electrolytic cells. Galvanic cells rely on spontaneous redox reactions to generate electrical energy, with electrons moving voluntarily from higher to lower potential without external aid. Electrolytic cells, however, drive nonspontaneous reactions by inputting electrical energy from an outside source, overriding the natural tendency and directing electron flow. The energy flow—output in galvanic versus input in electrolytic—directly influences the direction and feasibility of electron movement in the circuit. Choice D is a common distractor, wrongly labeling it as electrolytic with a spontaneous reaction, based on the misconception that all processes producing visible products like gases or metals must be spontaneous regardless of energy input. To distinguish between cell types, remember: if electrical energy is produced, the cell is galvanic; if it must be supplied, the cell is electrolytic.

Question 17

A student uses a rechargeable lithium-ion battery to power a phone (discharging). During use, the battery provides electrical energy to the circuit without being connected to a charger. Which statement correctly classifies the process occurring during discharge and its defining feature?

  1. Electrolytic cell; an external power source is required to force a nonspontaneous redox reaction
  2. Galvanic (voltaic) cell; a spontaneous redox reaction produces electrical energy in the external circuit (correct answer)
  3. Galvanic (voltaic) cell; an external power source is required to force a nonspontaneous redox reaction
  4. Electrolytic cell; a spontaneous redox reaction produces electrical energy in the external circuit
  5. Galvanic (voltaic) cell; the separator membrane supplies electrons to the circuit

Explanation: This question tests your understanding of galvanic (voltaic) and electrolytic cells. In galvanic cells, spontaneous processes generate electrical energy, with natural electron flow. Electrolytic cells require external energy to drive nonspontaneous processes, forcing electron direction. This spontaneity-energy relationship distinguishes cells and determines electron movement. Choice C is a tempting choice, misclassifying it as galvanic needing power, based on the misconception that batteries always require external input even during discharge. To distinguish between cell types, remember: if electrical energy is produced, the cell is galvanic; if it must be supplied, the cell is electrolytic.

Question 18

In a lab demonstration, an electrochemical device is connected to a small LED. The LED lights continuously for several minutes with no external power source, while one metal electrode becomes pitted and the other gains mass. Which statement best classifies the device and its defining feature?

  1. It is an electrolytic process that requires electrical energy input to drive a nonspontaneous reaction.
  2. It is an electrolytic process that produces electrical energy from a spontaneous reaction.
  3. It is a galvanic process that produces electrical energy from a spontaneous reaction. (correct answer)
  4. It is a galvanic process that requires electrical energy input to drive a nonspontaneous reaction.
  5. It is an electrolytic process in which the salt bridge provides the electrical energy that drives the reaction.

Explanation: This question tests understanding of galvanic (voltaic) and electrolytic cells. The key observation is that the LED lights continuously without any external power source, proving the cell generates its own electrical energy. Galvanic cells produce electrical energy from spontaneous redox reactions, where one metal oxidizes (becomes pitted as it loses mass) while ions at the other electrode reduce (gaining mass as metal deposits). This spontaneous electron flow powers the LED. Electrolytic cells, in contrast, require external electrical energy input and cannot power external devices. Choice B incorrectly suggests a galvanic process could require energy input, which is a contradiction since galvanic cells by definition produce energy. To identify a galvanic cell, look for electrical energy output without external power sources.

Question 19

A student places two graphite electrodes into water containing a small amount of dissolved electrolyte to increase conductivity and connects the electrodes to a DC power supply. Gas bubbles form at both electrodes only while the power supply is on. Which statement best describes the process and the role of electrical energy?

  1. It is a galvanic process that produces electrical energy from a spontaneous reaction.
  2. It is a galvanic process that requires electrical energy input to drive a nonspontaneous reaction.
  3. It is an electrolytic process that requires electrical energy input to drive a nonspontaneous reaction. (correct answer)
  4. It is an electrolytic process that produces electrical energy from a spontaneous reaction.
  5. It is a galvanic process in which the salt bridge provides the electrical energy that drives the reaction.

Explanation: This question tests understanding of galvanic (voltaic) and electrolytic cells. The crucial observation is that gas bubbles form only while the power supply is on, indicating the water electrolysis reaction (2H₂O → 2H₂ + O₂) is nonspontaneous and requires continuous electrical energy input. Electrolytic cells use electrical energy to drive nonspontaneous reactions, and the immediate cessation of bubbling when power is removed confirms this classification. In contrast, galvanic cells produce electrical energy from spontaneous reactions and would continue briefly even after disconnection. The formation of hydrogen at the cathode and oxygen at the anode is characteristic of water electrolysis. Choice A incorrectly suggests this could be galvanic, but galvanic cells never require external power to operate. Remember that processes requiring constant external power are always electrolytic.

Question 20

A cell is assembled with two half-cells connected by a salt bridge and a wire. The wire is connected to a voltmeter, which reads approximately 0 V. When a battery is then connected in series with the cell, a steady current flows and one electrode becomes coated with metal. Which statement correctly classifies the process occurring while the battery is connected and identifies a defining feature?​

  1. It is a galvanic (voltaic) cell because the battery supplies electrons that make the reaction spontaneous.
  2. It is an electrolytic cell because an external power source is required to force the redox reaction and produce metal plating. (correct answer)
  3. It is a galvanic (voltaic) cell because a reading of 0 V indicates maximum driving force for a spontaneous reaction.
  4. It is an electrolytic cell because the salt bridge is the source of the voltage needed to run the reaction.
  5. It is a galvanic (voltaic) cell because metal plating can occur only when electrical energy is produced.

Explanation: This question tests understanding of galvanic (voltaic) and electrolytic cells. The initial 0 V reading indicates no spontaneous reaction occurs, but when the battery is connected, it supplies electrical energy to drive a nonspontaneous redox reaction, defining an electrolytic cell. The battery forces oxidation at one electrode and reduction (metal plating) at the other, overcoming the thermodynamic barrier. Choice C incorrectly interprets 0 V as maximum driving force, when it actually means no driving force exists for spontaneous reaction. The strategy is that if a battery must be added to make a reaction proceed, the process is electrolytic.