AP Chemistry Quiz: Physical And Chemical Changes

What this quiz covers

This quiz focuses on Physical And Chemical Changes, 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.

Question 1

1. Chemical change, because increasing pressure forces N2 molecules to bond together into larger molecules
2. Physical change, because the molecules remain N2 and only the spacing between particles changes (correct answer)
3. Chemical change, because pressure is a form of energy that creates new substances
4. Chemical change, because the gas becomes denser, which means the particles must be different
5. Physical change, because the pressure change proves that the gas has reacted completely

Explanation: This question tests understanding of physical and chemical changes. In a physical change, particle identity remains the same while arrangement or spacing changes, whereas chemical changes create new substances with different compositions. When the syringe plunger compresses nitrogen gas, the N2 molecules remain N2—they simply move closer together as volume decreases. No new substances form; the particles maintain their diatomic nitrogen identity throughout compression. Choice A incorrectly claims N2 molecules bond together, but compression doesn't cause nitrogen molecules to react with each other. The strategy is to determine whether particle composition changes—if molecules remain the same formula, it's physical.

Question 2

1. Chemical change, because breaking a substance changes the bonds between copper atoms into a new compound
2. Physical change, because the particles remain copper atoms in a metallic lattice; only the shape and size of the sample change (correct answer)
3. Chemical change, because the copper becomes two substances after it breaks
4. Chemical change, because the copper is work-hardened, which means its composition changes
5. Physical change, because any process done by hand cannot be chemical

Explanation: This question tests understanding of physical and chemical changes. Physical changes alter shape, size, or arrangement without changing particle identity, while chemical changes create new substances. When copper metal is bent and broken, the Cu atoms remain Cu atoms in a metallic lattice—only the macroscopic shape changes as the metal fractures. No new substances form; the copper maintains its elemental identity and metallic bonding throughout the mechanical stress. Choice A incorrectly claims breaking changes bonds into new compounds, but mechanical fracture doesn't alter atomic identity. The strategy is to ask whether the chemical formula or composition changes—if not, it's physical.

Question 3

1. Chemical change, because the NaCl is converted into new substances that cannot be recovered by evaporating the water
2. Physical change, because the identities of the particles remain Na+ and Cl− in solution and NaCl(s) can be recovered by removing the water (correct answer)
3. Chemical change, because dissolving always breaks ionic bonds permanently and creates new ions that were not present before
4. Chemical change, because any process that makes a solid "disappear" in water must involve a reaction
5. Physical change, because a temperature change is observed during stirring, and temperature changes indicate physical processes

Explanation: This question tests understanding of physical and chemical changes. In a chemical change, the identity of particles changes as new substances with different compositions form, while in a physical change, particles maintain their identity but may rearrange or change state. When NaCl dissolves in water, the ionic solid separates into Na+ and Cl- ions that were already present in the crystal lattice—no new particles form. The fact that solid NaCl can be recovered by evaporation confirms the ions' identities remained unchanged throughout the process. Choice A incorrectly claims new substances form, but dissolving is merely the separation of existing ions. The key strategy is to ask whether the fundamental particle identities change—if not, the change is physical.

Question 4

1. Chemical change, because ions form when the salt is added to water
2. Physical change, because the solution is clear and colorless
3. Chemical change, because the solid disappears and therefore must have been consumed
4. Physical change, because $\mathrm{Na^+}$ and $\mathrm{Cl^-}$ ions separate and become surrounded by water molecules without forming a new substance (correct answer)
5. Chemical change, because the solution is homogeneous after stirring

Explanation: This question tests understanding of physical and chemical changes. A chemical change occurs when particles' identities change through atomic rearrangement to form new substances, while a physical change involves the same particles changing their arrangement or state without forming new substances. When NaCl dissolves in water, the ionic solid separates into Na⁺ and Cl⁻ ions that already existed in the crystal lattice—these ions simply become surrounded by water molecules through hydration, but no new substances form. The tempting distractor C incorrectly claims this is a chemical change because ions form, but the ions were already present in solid NaCl; dissolving merely separates and hydrates them. To distinguish physical from chemical changes, ask whether the fundamental particle identities remain the same or whether atoms rearrange to create substances with new chemical formulas.

Question 5

1. Chemical change, because the mixture is no longer uniform after separation
2. Chemical change, because a force is applied to the particles
3. Chemical change, because the magnet changes iron into a different form of matter
4. Physical change, because the substances are separated without changing the identity of the particles (correct answer)
5. Physical change, because the mass of the separated iron is less than the mass of the original mixture

Explanation: This question tests understanding of physical and chemical changes. In a physical change, particles maintain their chemical identity while changing only their arrangement or location, whereas in a chemical change, atoms rearrange to form new substances with different compositions. When a magnet separates iron filings from sand, the iron particles remain Fe atoms and sand remains SiO₂—no new substances form, and the particles are simply sorted based on their magnetic properties. The tempting distractor A incorrectly suggests the magnet chemically changes iron into a different form, but magnetic attraction is a physical property that doesn't alter atomic structure or create new substances. To recognize physical changes, ask whether the separation or rearrangement can be reversed without chemical reaction and whether particle identities remain unchanged.

Question 6

1. Chemical change, because the solution conducts electricity, indicating a new substance formed
2. Physical change, because NaCl remains as neutral formula units dispersed in water
3. Physical change, because Na+ and Cl− ions separate and become hydrated, but no new substances are formed (correct answer)
4. Chemical change, because dissolving always produces new substances
5. Chemical change, because the solid disappears, meaning it was consumed in a reaction

Explanation: This question tests understanding of physical and chemical changes. In a chemical change, particle identity changes as atoms rearrange to form new substances, while in a physical change, particles may separate or rearrange but maintain their fundamental identity. When NaCl dissolves, the ionic solid separates into Na+ and Cl- ions that become surrounded by water molecules (hydrated), but these are the same ions that existed in the solid—no new substances form. The tempting distractor A is incorrect because electrical conductivity results from mobile ions, not new substance formation. To determine if a change is physical or chemical, ask whether new substances with new compositions form—if the same particles exist before and after, just in different arrangements, it's physical.

Question 7

1. Physical change, because heating can change the texture of a metal without changing what it is made of.
2. Chemical change, because magnesium atoms become part of a different substance with different particle composition than the original metal. (correct answer)
3. Physical change, because the mass of the sample stays the same during heating.
4. Physical change, because the product is a solid just like the original magnesium.
5. Chemical change, because any time a substance is heated, its bonds must break and reform.

Explanation: This question tests understanding of physical and chemical changes. In a chemical change, particle identity changes as atoms rearrange to form new substances with different compositions, while physical changes preserve particle identity. When magnesium metal burns in air, it reacts with oxygen to form magnesium oxide (MgO), a completely different substance where magnesium atoms are now bonded to oxygen atoms in an ionic compound rather than existing as metallic magnesium. Choice A incorrectly suggests this is merely a texture change, but the white powder has fundamentally different particle composition (Mg²⁺ and O²⁻ ions) than the original metal (Mg atoms). To distinguish physical from chemical changes, examine whether atoms have formed new bonds with different elements—if the particle composition changes, it's chemical.

Question 8

1. Chemical change, because the NaCl(s) disappears, meaning it was consumed
2. Physical change, because Na$^+$ and Cl$^-$ ions become dispersed in water without forming new substances (correct answer)
3. Chemical change, because ions are produced and ions are different substances than the solid
4. Chemical change, because dissolving always involves breaking bonds
5. Physical change, because NaCl(s) changes into NaCl(l)

Explanation: This question tests understanding of physical and chemical changes. In a chemical change, particles transform into new substances with different compositions, while in a physical change, particles maintain their identity but may separate or rearrange. When NaCl dissolves in water, the ionic solid separates into Na⁺ and Cl⁻ ions that already existed in the crystal lattice—no new substances form. The ions simply become surrounded by water molecules and dispersed throughout the solution, maintaining their chemical identity. Choice C incorrectly suggests that producing ions means creating new substances, but these ions were already present in the solid NaCl structure. To identify physical versus chemical changes, ask yourself: 'Are the same types of particles present before and after, just in different arrangements or states?'

Question 9

1. Physical change, because NaCl is only changing from molten to separated components
2. Physical change, because the process occurs in the liquid state
3. Chemical change, because ions are converted into different particles (neutral Na atoms and Cl2 molecules) (correct answer)
4. Physical change, because electricity cannot change particle identity
5. Chemical change, because any change that produces a gas is chemical even if particle identity stays the same

Explanation: This question tests understanding of physical and chemical changes. In a chemical change, particle identity changes as atoms rearrange to form new substances with different compositions, while in a physical change, particles maintain their identity. During electrolysis of molten NaCl, Na+ ions gain electrons to become neutral Na atoms (silvery metal), and Cl- ions lose electrons to form Cl2 molecules (greenish-yellow gas)—the particles' identities fundamentally change. The tempting distractor A is incorrect because this isn't just separation; the ions are converted into entirely different particles through electron transfer. To identify chemical changes, ask whether new substances with new compositions form—if particles gain or lose electrons to become different species, it's chemical.

Question 10

1. Physical change, because the magnesium is simply dissolving into smaller pieces
2. Chemical change, because new particles (including a gas) form as magnesium atoms become part of different substances (correct answer)
3. Physical change, because bubbles indicate boiling of the solution
4. Physical change, because the total mass of matter is conserved
5. Chemical change, because the magnesium changes shape

Explanation: This question tests understanding of physical and chemical changes. A chemical change occurs when particles change identity to form new substances with different compositions, while a physical change involves the same particles rearranging or changing phase. When magnesium reacts with hydrochloric acid, the Mg atoms become Mg²⁺ ions while H⁺ ions from the acid become H₂ gas molecules—completely new substances form with different particle identities. The bubbles indicate hydrogen gas formation, a new substance that wasn't present initially. Choice A incorrectly suggests this is merely dissolving, but dissolving doesn't produce gas or consume the metal through reaction. To distinguish physical from chemical changes, check whether the products contain different types of particles than the reactants—if yes, it's chemical.

Question 11

1. Physical change, because the copper is still copper but with a different color
2. Chemical change, because copper atoms at the surface become part of new compounds in the coating (correct answer)
3. Physical change, because moisture causes copper to dissolve slightly and redeposit
4. Chemical change, because any color change is always a chemical reaction
5. Physical change, because the coating can be scraped off

Explanation: This question tests understanding of physical and chemical changes. A chemical change involves particles changing identity to form new substances, while a physical change maintains particle identity with only rearrangement or phase changes. When copper develops a green coating (patina), copper atoms react with oxygen, water, and carbon dioxide to form new compounds like copper carbonate and copper hydroxide—substances with completely different particle compositions than metallic copper. The green coating consists of new chemical compounds, not just rearranged copper atoms. Choice A incorrectly suggests the copper remains unchanged, but the surface copper atoms have become part of entirely different substances. To determine change type, examine whether the particles present after the change have different chemical formulas than those present initially.

Question 12

1. Chemical change, because iodine molecules break apart into iodine atoms in the vapor.
2. Physical change, because I$_2$ molecules remain intact and only the physical state changes from solid to gas. (correct answer)
3. Chemical change, because a gas is produced, which indicates new substances formed.
4. Chemical change, because the purple color indicates a new compound was formed.
5. Physical change, because the iodine must have dissolved in air as a solute.

Explanation: This question tests the skill of distinguishing between physical and chemical changes. Chemical changes involve altering particle identity by breaking bonds and forming new ones, leading to substances with different chemical compositions. Physical changes preserve the identity of particles, often involving phase transitions or rearrangements where molecules stay intact but change state or position. Here, the iodine undergoes sublimation, a physical change, as I2 molecules transition from solid to gas without any change in their molecular structure or composition. One tempting distractor is choice C, which is incorrect because gas production can occur in physical processes like boiling or sublimation, not just chemical reactions. To classify changes reliably, ask whether new substances with new compositions form; if the particles remain the same, it is physical.

Question 13

1. Chemical change, because the purple color indicates iodine has reacted to form a new substance
2. Physical change, because I2 particles remain I2 and only the physical state changes from solid to gas (correct answer)
3. Chemical change, because solids cannot change directly into gases without reacting
4. Chemical change, because a visible change always means new substances have formed
5. Physical change, because the container is closed, so reactions are not possible

Explanation: This question tests understanding of physical and chemical changes. Physical changes alter arrangement or state while maintaining particle identity, whereas chemical changes create new substances with different compositions. When solid iodine sublimes, I2 molecules transition directly from solid to gas phase, but remain I2 throughout—no new substances form. The purple vapor consists of the same I2 molecules that were in the solid, just in a different physical state with greater spacing. Choice C incorrectly claims solids cannot become gases without reacting, but sublimation is a well-known physical process. The key is to check whether the chemical formula changes—if particles keep the same formula, it's physical.

Question 14

1. Physical change, because heating can only change the size and shape of a substance, not its identity
2. Chemical change, because the magnesium atoms combine with oxygen from the air to form particles with a different composition than Mg(s) (correct answer)
3. Physical change, because the color change indicates the metal was ground into a finer powder
4. Physical change, because the mass of the sample would stay constant in an open container during heating
5. Chemical change, because any change in electrical conductivity must be caused by a phase change

Explanation: This question tests understanding of physical and chemical changes. A chemical change occurs when particle identity changes to form new substances with different compositions, while a physical change involves rearrangement or state changes without altering particle identity. When magnesium metal is heated in air, it reacts with oxygen to form magnesium oxide (MgO), a new compound with a different composition than elemental Mg. The white powder's inability to conduct electricity confirms it's no longer metallic magnesium but an ionic compound. Choice C incorrectly suggests the color change is from grinding, but heating doesn't mechanically grind metals. To identify change type, check if new substances with new chemical formulas form—if yes, it's chemical.

Question 15

1. Physical change, because the nail is still solid iron and only the appearance has changed
2. Chemical change, because iron atoms combine with oxygen (and water) to form particles with a different composition than Fe(s) (correct answer)
3. Physical change, because the coating is just dirt from the water sticking to the nail
4. Chemical change, because any color change is always evidence of a chemical reaction, regardless of particle identity
5. Physical change, because the coating forms slowly, and slow changes are physical

Explanation: This question tests understanding of physical and chemical changes. Chemical changes form new substances with different compositions, while physical changes only alter appearance or arrangement. When iron rusts in water and air, Fe atoms react with oxygen (and water) to form iron oxide compounds like Fe2O3·nH2O—new substances with different compositions than elemental iron. The reddish-brown coating that cannot be rinsed away confirms a new compound has formed on the surface. Choice C incorrectly suggests the coating is just dirt, but dirt would rinse off with water while rust is chemically bonded. To determine change type, check if new compounds with different formulas form—rust has a different formula than iron metal.

Question 16

1. Physical change, because bubbles indicate a liquid is boiling due to mixing
2. Physical change, because the zinc is only breaking into smaller pieces as it is stirred by the liquid
3. Chemical change, because gas bubbles and the disappearance of Zn(s) indicate formation of particles different from Zn(s) and HCl(aq) (correct answer)
4. Physical change, because acids dissolve metals without changing what the metal is made of
5. Chemical change, because the test tube gets warmer, and temperature increase always means a chemical reaction occurred

Explanation: This question tests understanding of physical and chemical changes. Chemical changes produce new substances with different particle identities, while physical changes maintain particle identity despite appearance changes. When zinc reacts with hydrochloric acid, the Zn atoms lose electrons to form Zn2+ ions while H+ ions gain electrons to form H2 gas—both are new substances with different compositions than the reactants. The bubbles (hydrogen gas) and disappearing zinc confirm a chemical reaction is occurring. Choice A incorrectly attributes bubbles to boiling, but boiling requires heating and doesn't consume solid metal. To identify change type, look for evidence of new substances forming, such as gas production from non-gaseous reactants.

Question 17

1. Chemical change, because the formation of fog indicates CO$_2$ reacted to form H$_2$O(l).
2. Physical change, because CO$_2$ molecules remain CO$_2$ as the solid changes directly to gas. (correct answer)
3. Chemical change, because a solid turning into a gas requires breaking covalent bonds within CO$_2$.
4. Chemical change, because gases produced from solids are always reaction products.
5. Physical change, because the fog proves the CO$_2$ is dissolving into liquid water in the beaker.

Explanation: This question tests the skill of distinguishing between physical and chemical changes. Chemical changes involve particle identity shifts, like breaking molecular bonds to form new substances during sublimation if decomposition occurred. Physical changes keep particles identical, such as in sublimation where solids turn to gas directly, maintaining molecular structure. Dry ice subliming is physical as CO2 molecules transition from solid to gas unchanged, with fog from air moisture, not a reaction product. A tempting distractor is choice C, which is incorrect because sublimation involves overcoming intermolecular forces, not breaking covalent bonds within CO2 molecules. To classify changes reliably, ask whether new substances with new compositions form; if the gas is the same as the solid's particles, it is physical.

Question 18

1. Chemical change, because dissolving always involves breaking chemical bonds to make new substances.
2. Physical change, because any change that occurs in water must be a phase change of H$_2$O.
3. Chemical change, because the solution conducts electricity, which indicates a new substance formed.
4. Chemical change, because the disappearance of the solid means NaCl decomposed into Na(s) and Cl$_2$(g).
5. Physical change, because NaCl units separate into hydrated Na$^+$ and Cl$^-$ ions without creating new types of particles. (correct answer)

Explanation: This question tests the skill of distinguishing between physical and chemical changes. A chemical change involves the formation of new substances where the identity of particles changes, such as through bond breaking and forming to create different molecules or ions with new compositions. In contrast, a physical change involves no alteration in particle identity; instead, particles may rearrange, separate, or undergo phase changes while remaining the same substance. For dissolving NaCl in water, the process is physical because the NaCl dissociates into Na+ and Cl- ions surrounded by water, but these ions are the same particles present in the solid, just separated and hydrated. One tempting distractor is choice A, which is incorrect because conductivity indicates the presence of mobile ions, not necessarily the formation of new substances, as the ions were already part of the NaCl lattice. To classify changes reliably, ask whether new substances with new compositions form; if not, it is physical.

Question 19

1. Physical change, because the ions are still present in the beaker and no atoms are created or destroyed.
2. Chemical change, because ions rearrange to form a new solid substance with particles different from those in the original solutions. (correct answer)
3. Physical change, because the solid formed is just undissolved NaCl that was already present.
4. Physical change, because the appearance of a solid always indicates freezing.
5. Chemical change, because stirring two solutions always causes a reaction.

Explanation: This question tests the skill of distinguishing between physical and chemical changes. In a chemical change, the identity of particles changes as they form new bonds, creating substances with entirely new compositions, such as in precipitation reactions. Physical changes do not alter particle identity; they might involve mixing, separating, or phase changes where the original substances remain unchanged. Mixing silver nitrate and sodium chloride results in a chemical change because silver and chloride ions combine to form insoluble AgCl, a new solid with a different composition from the original ions. A tempting distractor is choice A, which is incorrect because while ions are conserved, their rearrangement into a new compound with distinct properties constitutes a chemical change, not just preservation. To classify changes reliably, ask whether new substances with new compositions form; if a new compound precipitates, it is chemical.

Question 20

1. Physical change, because the catalyst only speeds up a process and cannot change particle identity.
2. Chemical change, because new particles (including O$_2$ molecules) form from H$_2$O$_2$. (correct answer)
3. Physical change, because bubbles indicate boiling of the solution.
4. Physical change, because the potato surface provides nucleation sites for dissolved air to come out of solution.
5. Chemical change, because any reaction that produces bubbles must involve carbon dioxide.

Explanation: This question tests the skill of distinguishing between physical and chemical changes. Chemical changes involve changing particle identity, such as decomposition where molecules break down into new substances with different compositions. Physical changes do not alter identity; they might include bubbling from boiling or gas release without reaction. The hydrogen peroxide decomposes into water and oxygen gas, a chemical change, as H2O2 molecules form new O2 molecules, confirmed by the relit splint test for oxygen. One tempting distractor is choice C, which is wrong because bubbles can form in chemical decompositions, not just physical boiling, and the catalyst accelerates the reaction without heating. To classify changes reliably, ask whether new substances with new compositions form; if a gas like O2 is produced from decomposition, it is chemical.