Ch.14 - Chemical Kinetics

Brown - Chemistry: The Central Science 15th Edition

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Brown 15th Edition

Ch.14 - Chemical Kinetics

Problem 57c

Chapter 14, Problem 57c

Indicate whether each statement is true or false. (c) Increasing the reaction temperature increases the fraction of successful collisions between reactants.

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Understand the concept of activation energy, which is the minimum energy that reactant molecules must possess in order to undergo a successful chemical reaction.

Recognize that at higher temperatures, the kinetic energy of the molecules increases. This means that more molecules will have energies equal to or greater than the activation energy.

Consider the Maxwell-Boltzmann distribution which shows that as temperature increases, the curve flattens and broadens, indicating that a larger fraction of molecules have higher energies.

Relate the increase in the number of molecules with sufficient energy (above the activation energy) to the likelihood of successful collisions. Successful collisions are those that result in a chemical reaction.

Conclude that increasing the reaction temperature does indeed increase the fraction of successful collisions between reactants, as more reactant molecules have the necessary energy to overcome the activation energy barrier.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Collision Theory

Collision theory states that for a reaction to occur, reactant particles must collide with sufficient energy and proper orientation. The frequency and energy of these collisions are influenced by factors such as temperature, which affects the kinetic energy of the particles.

Effect of Temperature on Reaction Rate

Increasing the temperature generally increases the kinetic energy of molecules, leading to more frequent and more energetic collisions. This results in a higher fraction of collisions that have enough energy to overcome the activation energy barrier, thus increasing the reaction rate.

Activation Energy

Activation energy is the minimum energy required for a chemical reaction to occur. When temperature rises, more molecules possess energy equal to or greater than this threshold, which increases the likelihood of successful collisions and, consequently, the rate of reaction.

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Related Practice

Textbook Question

Indicate whether each statement is true or false. (b) Exothermic reactions are faster than endothermic reactions.

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Textbook Question

Based on their activation energies and energy changes and assuming that all collision factors are the same, rank the following reactions from slowest to fastest. (a) Ea = 45 kJ>mol; E = -25 kJ>mol (b) Ea = 35 kJ>mol; E = -10 kJ>mol (c) Ea = 55 kJ>mol; E = 10 kJ>mol

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Textbook Question

The gas-phase reaction Cl(g) + HBr(g) → HCl(g) + Br(g) has an overall energy change of -66 kJ. The activation energy for the reaction is 7 kJ. (b) What is the activation energy for the reverse reaction?

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Textbook Question

Indicate whether each statement is true or false. (a) If you measure the rate constant for a reaction at different temperatures, you can calculate the overall enthalpy change for the reaction.

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Textbook Question

The gas-phase reaction Cl(g) + HBr(g) → HCl(g) + Br(g) has an overall energy change of -66 kJ. The activation energy for the reaction is 7 kJ. (a) Sketch the energy profile for the reaction, and label Ea and ΔE.

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