Question

Most reactions are exothermic, even if they give off heat at such a slow rate that we cannot perceive it. (This is the case with something rusting. It is a highly exothermic reaction, but happens very slowly. ) When reactions are exothermic, heat can be thought of as a product of the reaction. In general, we say that we can increase the rate of a reaction (the production of products) by heating the reaction. Why does heating a reaction vessel cause the reaction to go quicker and produce more products?

In terms of equilibrium, according to LeChatelier’s principle, what shift would occur when an exothermic reaction is heated? (Would more reactants or products be made?)

Does LeChatelier’s principle agree with the first observation that heating increases the rate of production of products? Why or why not? If they do not agree, why do you think that is?

Answer 1

Heating a reaction vessel increases the kinetic energy of the reactant molecules, which makes them move faster and collide more frequently. This leads to more successful collisions, which increases the rate of the reaction and the production of products. Additionally, increasing the temperature can lower the activation energy required for the reaction to occur, making it easier for the reaction to proceed.

According to LeChatelier's principle, when an exothermic reaction is heated, the equilibrium will shift towards the side with the fewer number of moles of gas. This is because heating an exothermic reaction is equivalent to adding heat as a product, and the system will try to counteract the increase in heat by shifting towards the side with fewer moles of gas. However, it's important to note that this shift in equilibrium is different from the increase in reaction rate caused by heating. The increase in reaction rate is due to the faster molecular motion, while the shift in equilibrium is due to the system's attempt to maintain a constant temperature.

LeChatelier's principle agrees with the observation that heating increases the rate of production of products, but they are not directly related. The principle explains the shift in equilibrium caused by changes in temperature, pressure, or concentration, while the increase in reaction rate caused by heating is a kinetic effect that doesn't involve changes in the equilibrium constant.

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