AP Chemistry Flashcards: Introduction To Reaction Mechanisms

What this deck covers

This deck focuses on Introduction To Reaction Mechanisms, giving you a quick way to review the definitions, rules, and examples that matter most for AP Chemistry.

How to use these flashcards

Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: Define termolecular reaction.

Answer: An elementary reaction involving three molecules. Very rare due to low probability of three molecules colliding simultaneously.

Flashcard 2: What is a unimolecular reaction?

Answer: A reaction involving a single molecule undergoing change. Has molecularity of one and follows first-order kinetics.

Flashcard 3: What does the term 'reaction order' refer to?

Answer: The sum of the exponents in the rate law expression. Determines how concentration changes affect overall rate.

Flashcard 4: What does 'R' represent in the Arrhenius equation?

Answer: The universal gas constant. Fundamental constant linking energy and temperature scales.

Flashcard 5: What is a reaction intermediate?

Answer: Species formed in one step of a mechanism and consumed in another. Temporary species that appear in mechanism but not in overall equation.

Flashcard 6: What is the effect of a catalyst on activation energy?

Answer: A catalyst lowers the activation energy of a reaction. Provides alternative pathway requiring less energy input.

Flashcard 7: What is the significance of the rate-determining step?

Answer: It limits the overall reaction rate. Slowest step controls overall reaction speed like bottleneck.

Flashcard 8: What is the steady-state approximation?

Answer: An assumption that the concentration of intermediates remains constant. Rate of formation equals rate of consumption for intermediates.

Flashcard 9: What is the transition state theory?

Answer: A theory that explains reaction rates by considering the transition state. Links thermodynamics and kinetics through activated complex formation.

Flashcard 10: What does the term 'rate law' refer to?

Answer: An equation that relates the rate of reaction to the concentration of reactants. Mathematical expression relating reaction rate to concentrations.

Flashcard 11: What is the effect of temperature on the rate constant $k$?

Answer: Typically, $k$ increases with increasing temperature. Exponential relationship described by Arrhenius equation.

Flashcard 12: What is the significance of the rate-determining step?

Answer: It limits the overall reaction rate. Slowest step controls overall reaction speed like bottleneck.

Flashcard 13: Define 'molecularity' in reaction mechanisms.

Answer: The number of molecules that participate in an elementary reaction. Applies only to elementary reactions, not overall mechanisms.

Flashcard 14: What is the half-life ($t_{1/2}$) of a first-order reaction?

Answer: $t_{1/2} = \frac{0.693}{k}$. Time required for concentration to decrease by half.

Flashcard 15: What does the term 'rate law' refer to?

Answer: An equation that relates the rate of reaction to the concentration of reactants. Mathematical expression relating reaction rate to concentrations.

Flashcard 16: What is the difference between a catalyst and an intermediate?

Answer: Catalysts are not consumed; intermediates are formed and consumed. Both help reaction proceed but have different consumption patterns.

Flashcard 17: Identify the role of a catalyst in a reaction mechanism.

Answer: A substance that increases reaction rate without being consumed. Lowers activation energy by providing alternative pathway.

Flashcard 18: Define 'reaction profile'.

Answer: A graph showing the energy changes during a reaction. Visualizes energy barriers and intermediates along reaction pathway.

Flashcard 19: What is the steady-state approximation?

Answer: An assumption that the concentration of intermediates remains constant. Rate of formation equals rate of consumption for intermediates.

Flashcard 20: Define 'reaction profile'.

Answer: A graph showing the energy changes during a reaction. Visualizes energy barriers and intermediates along reaction pathway.

Flashcard 21: How does a catalyst affect a reaction mechanism?

Answer: It provides an alternative pathway with lower activation energy. Reduces activation energy without changing thermodynamics.

Flashcard 22: What is the typical unit for the universal gas constant ($R$)?

Answer: $8.314 J mol^{-1} K^{-1}$. Standard SI units for gas constant in energy calculations.

Flashcard 23: How does temperature affect reaction rate according to the Arrhenius equation?

Answer: Increasing temperature increases the reaction rate. Higher temperature increases molecular energy and collision frequency.

Flashcard 24: Identify the units of a rate constant for a second-order reaction.

Answer: $M^{-1}s^{-1}$. Units account for concentration dependence in second-order kinetics.

Flashcard 25: Identify the units of a rate constant for a zero-order reaction.

Answer: $M s^{-1}$. Units reflect constant rate independent of concentration.

Flashcard 26: Define termolecular reaction.

Answer: An elementary reaction involving three molecules. Very rare due to low probability of three molecules colliding simultaneously.

Flashcard 27: How does temperature affect reaction rate according to the Arrhenius equation?

Answer: Increasing temperature increases the reaction rate. Higher temperature increases molecular energy and collision frequency.

Flashcard 28: Identify the transition state of a reaction.

Answer: A high-energy, unstable arrangement of atoms at the peak of a reaction coordinate. Maximum energy point along reaction coordinate diagram.

Flashcard 29: Identify the transition state of a reaction.

Answer: A high-energy, unstable arrangement of atoms at the peak of a reaction coordinate. Maximum energy point along reaction coordinate diagram.

Flashcard 30: State the formula for the Arrhenius equation.

Answer: $k = Ae^{-Ea/RT}$. Shows exponential dependence of rate constant on temperature.

Flashcard 31: What does the symbol $k$ represent in kinetics?

Answer: The rate constant of a reaction. Proportionality constant in rate law expressions.

Flashcard 32: Define 'reaction coordinate'.

Answer: A hypothetical path that represents the progress of a reaction. X-axis in energy diagrams showing reaction progress.

Flashcard 33: What is the difference between a catalyst and an intermediate?

Answer: Catalysts are not consumed; intermediates are formed and consumed. Both help reaction proceed but have different consumption patterns.

Flashcard 34: What is the half-life ($t_{1/2}$) of a first-order reaction?

Answer: $t_{1/2} = \frac{0.693}{k}$. Time required for concentration to decrease by half.

Flashcard 35: What does the symbol $Ea$ represent in the Arrhenius equation?

Answer: Activation energy. Energy barrier parameter in temperature-dependent rate equation.

Flashcard 36: Define 'elementary reaction'.

Answer: A single step reaction with a single transition state and no intermediate. Cannot be broken down into simpler reaction steps.

Flashcard 37: What is a reaction mechanism?

Answer: A step-by-step sequence of elementary reactions by which an overall chemical change occurs. Describes the detailed pathway showing how reactants become products.

Flashcard 38: What is the rate-determining step?

Answer: The slowest step in a reaction mechanism that determines the overall rate. Acts as bottleneck controlling overall reaction speed.

Flashcard 39: What is the Lindemann mechanism?

Answer: A mechanism describing unimolecular reactions through a two-step process. Explains pressure dependence of unimolecular reaction rates.

Flashcard 40: Identify the units of a rate constant for a second-order reaction.

Answer: $M^{-1}s^{-1}$. Units account for concentration dependence in second-order kinetics.

Flashcard 41: What is a unimolecular reaction?

Answer: A reaction involving a single molecule undergoing change. Has molecularity of one and follows first-order kinetics.

Flashcard 42: Define 'reaction coordinate'.

Answer: A hypothetical path that represents the progress of a reaction. X-axis in energy diagrams showing reaction progress.

Flashcard 43: What is the effect of a catalyst on activation energy?

Answer: A catalyst lowers the activation energy of a reaction. Provides alternative pathway requiring less energy input.

Flashcard 44: What is the purpose of using the steady-state approximation?

Answer: To simplify the analysis of complex reaction mechanisms. Eliminates need to track rapidly changing intermediate concentrations.

Flashcard 45: What is a reaction mechanism?

Answer: A step-by-step sequence of elementary reactions by which an overall chemical change occurs. Describes the detailed pathway showing how reactants become products.

Flashcard 46: How does molecular orientation affect reaction rate?

Answer: Proper orientation during collisions is necessary for reaction. Molecules must collide with correct geometry for reaction.

Flashcard 47: Identify the role of a catalyst in a reaction mechanism.

Answer: A substance that increases reaction rate without being consumed. Lowers activation energy by providing alternative pathway.

Flashcard 48: Define 'elementary reaction'.

Answer: A single step reaction with a single transition state and no intermediate. Cannot be broken down into simpler reaction steps.

Flashcard 49: What does 'R' represent in the Arrhenius equation?

Answer: The universal gas constant. Fundamental constant linking energy and temperature scales.

Flashcard 50: What does a reaction mechanism describe?

Answer: The detailed steps of how a reaction proceeds from reactants to products. Shows elementary steps connecting reactants to products.

Flashcard 51: What is the transition state theory?

Answer: A theory that explains reaction rates by considering the transition state. Links thermodynamics and kinetics through activated complex formation.

Flashcard 52: What is the role of activation energy in a reaction mechanism?

Answer: The minimum energy required to initiate a chemical reaction. Energy barrier that must be overcome for reaction to occur.

Flashcard 53: How does molecular orientation affect reaction rate?

Answer: Proper orientation during collisions is necessary for reaction. Molecules must collide with correct geometry for reaction.

Flashcard 54: What characterizes a bimolecular reaction?

Answer: A reaction involving two reacting species. Has molecularity of two, most common elementary reaction type.

Flashcard 55: State the formula for the Arrhenius equation.

Answer: $k = Ae^{-Ea/RT}$. Shows exponential dependence of rate constant on temperature.

Flashcard 56: What is the purpose of using the steady-state approximation?

Answer: To simplify the analysis of complex reaction mechanisms. Eliminates need to track rapidly changing intermediate concentrations.

Flashcard 57: What is the rate-determining step?

Answer: The slowest step in a reaction mechanism that determines the overall rate. Acts as bottleneck controlling overall reaction speed.

Flashcard 58: What is the role of collision frequency in reaction rate?

Answer: Higher collision frequency can increase the reaction rate. More collisions per unit time increases reaction probability.

Flashcard 59: Identify the units of a rate constant for a first-order reaction.

Answer: $s^{-1}$. Units reflect inverse time for first-order processes.

Flashcard 60: What is the effect of concentration on reaction rate?

Answer: Increased concentration generally increases reaction rate. More reactant molecules lead to more frequent collisions.

Flashcard 61: How does a catalyst affect a reaction mechanism?

Answer: It provides an alternative pathway with lower activation energy. Reduces activation energy without changing thermodynamics.

Flashcard 62: What is the typical unit for the universal gas constant ($R$)?

Answer: $8.314 J mol^{-1} K^{-1}$. Standard SI units for gas constant in energy calculations.

Flashcard 63: What does the symbol $Ea$ represent in the Arrhenius equation?

Answer: Activation energy. Energy barrier parameter in temperature-dependent rate equation.

Flashcard 64: What characterizes a bimolecular reaction?

Answer: A reaction involving two reacting species. Has molecularity of two, most common elementary reaction type.

Flashcard 65: What is the role of activation energy in a reaction mechanism?

Answer: The minimum energy required to initiate a chemical reaction. Energy barrier that must be overcome for reaction to occur.

Flashcard 66: What does a reaction mechanism describe?

Answer: The detailed steps of how a reaction proceeds from reactants to products. Shows elementary steps connecting reactants to products.

Flashcard 67: What is the Lindemann mechanism?

Answer: A mechanism describing unimolecular reactions through a two-step process. Explains pressure dependence of unimolecular reaction rates.

Flashcard 68: Define 'molecularity' in reaction mechanisms.

Answer: The number of molecules that participate in an elementary reaction. Applies only to elementary reactions, not overall mechanisms.

Flashcard 69: Identify the units of a rate constant for a zero-order reaction.

Answer: $M s^{-1}$. Units reflect constant rate independent of concentration.

Flashcard 70: What is the effect of temperature on the rate constant $k$?

Answer: Typically, $k$ increases with increasing temperature. Exponential relationship described by Arrhenius equation.

Flashcard 71: What is the role of collision frequency in reaction rate?

Answer: Higher collision frequency can increase the reaction rate. More collisions per unit time increases reaction probability.

Flashcard 72: What does the term 'reaction order' refer to?

Answer: The sum of the exponents in the rate law expression. Determines how concentration changes affect overall rate.

Flashcard 73: What is the effect of concentration on reaction rate?

Answer: Increased concentration generally increases reaction rate. More reactant molecules lead to more frequent collisions.

Flashcard 74: Identify the units of a rate constant for a first-order reaction.

Answer: $s^{-1}$. Units reflect inverse time for first-order processes.

Flashcard 75: What does the symbol $k$ represent in kinetics?

Answer: The rate constant of a reaction. Proportionality constant in rate law expressions.