Question

Consider the following factors: increase in temperature, increase in concentration, and addition of a catalyst. Which increases the average kinetic energy of the reactants?

Short answer

Only the increase in temperature increases the average kinetic energy of the reactants.

Step-by-step solution

Understand factors that determine kinetic energy

Kinetic energy of a substance is dependent on its temperature, not on its concentration or the addition of a catalyst.

Analyze the effect of temperature on kinetic energy

When the temperature increases, the thermal energy of the particles also increases, leading them to move faster. Faster moving particles collide together with more energy. As kinetic energy of the particles is totally dependent on temperature, thus when there is an increase in temperature, the kinetic energy of the reactants in a reaction increases.

Analyze the effect of concentration and addition of catalyst on kinetic energy

While the rates of reactions can be affected by changes in concentration and the introduction of a catalyst, these factors don't affect a molecule's kinetic energy, which is dependent on temperature. Though an increase in concentration will increase the frequency of collisions between reactant molecules, and addition of a catalyst will speed up the reaction by providing an alternative reaction pathway with a lower activation energy, they don't alter the kinetic energy of individual molecules.

Key concepts

Effect of Temperature on Kinetic Energy

When it comes to understanding chemical kinetics, recognizing the relationship between temperature and kinetic energy is fundamental. Imagine a crowd of people; when it's cold, they tend to move sluggishly and interactions are minimal. But as the temperature rises, they become more animated, moving quicker and bumping into each other more often. This is analogous to particles in a chemical reaction.

As temperature increases, particles gain thermal energy which translates into motion - the faster they move, the higher their kinetic energy. This heightened energy results in more frequent and forceful collisions among reactant molecules. Thus, in the exercise, the answer to which factor increases the average kinetic energy of reactants is clear: an increase in temperature.

Reaction Rate Factors

Various factors can influence the rate at which chemical reactions occur. Temperature, as we discussed, plays a pivotal role by adjusting the kinetic energy of the molecules involved. However, other factors such as concentration and the use of catalysts also significantly impact the reaction rate.

• Concentration: By increasing the concentration of reactants, we increase the number of particles in a given volume, leading to a higher probability of collision and thus, a faster reaction rate.
• Presence of a Catalyst: Catalysts offer a shortcut in the reaction pathway, reducing the activation energy required for the reaction, which means reactions can proceed faster even at lower temperatures.

Although these factors expedite the process, they do not alter the inherent kinetic energy of individual molecules like temperature changes do.

Role of Catalyst in Reactions

A catalyst is often likened to a facilitator; it speeds up a reaction without being consumed by it, much like a coach helps athletes perform better without physically participating in the game. Adding a catalyst to a reaction introduces a new route for the reaction to occur - one that requires less energy to overcome the barrier to reaction (the activation energy).

This is crucial because it makes reactions feasible at lower temperatures or speeds them up at existing temperatures. In everyday terms, it's like applying lubricant to a sticky lock, allowing the key to turn more easily. Although catalysts can significantly increase reaction rates, as shown in the exercise, they do not affect the kinetic energy of the reactants, whereas temperature does.