Question

In a reversible reaction, how does the activation energy required for the exothermic change compare with the activation energy required for the endothermic change?

Short answer

The activation energy for the endothermic change is higher than that for the exothermic change.

Step-by-step solution

Understand the Terminology

A reversible reaction is one where the reactants can form products, which can then revert back to reactants. Activation energy is the energy required to initiate a reaction.

Identify the Changes

An exothermic change releases energy, while an endothermic change absorbs energy.

Analyze Activation Energies

In a reversible reaction, the activation energy for the exothermic change is the energy required to convert reactants to products, minus the energy released. The activation energy for the endothermic change is the energy required to convert products back to reactants, plus the energy absorbed.

Compare the Activation Energies

The activation energy for the endothermic change is always higher than that for the exothermic change, since it must overcome the energy that was released in the exothermic process and then some additional energy.

Key concepts

Reversible Reactions

In chemistry, reversible reactions are fascinating because they can go in both directions. This means the reactants can turn into products and the products can revert back to reactants. Imagine making a chemical soup that you can unmake back to its original ingredients. These reactions are very special and important in chemical processes and natural phenomena.
In a reversible reaction, there are two pathways: one for the forward reaction and one for the backward reaction. Each path requires energy to start, which we call the activation energy.
Understanding reversible reactions helps us predict how different factors like temperature affect the balance between reactants and products. It's a fundamental concept for students exploring the world of chemistry.

Exothermic Change

An exothermic change is when a chemical reaction releases energy, usually in the form of heat. Think of it like a campfire releasing warmth.
When a reaction is exothermic, the energy of the products is lower than the energy of the reactants. This means energy is given off during the reaction. The activation energy for an exothermic change is the energy you need to put in to start the reaction, minus the energy that gets released.
Some examples of exothermic reactions include the combustion of fuel, such as in a gasoline engine, or the rusting of iron. These reactions help to understand why certain processes feel warm or produce heat as they occur.

Endothermic Change

In contrast, an endothermic change is a reaction that absorbs energy. It feels like the opposite of an exothermic change; it’s like feeling a sudden chill when you dissolve salt in water.
For an endothermic reaction, the products have higher energy than the reactants. Energy needs to be supplied from outside the reaction to make it go. The activation energy for an endothermic change is higher because it must add the energy absorbed during the reaction.
Examples of endothermic reactions include photosynthesis, where plants absorb sunlight to create food, and the melting of ice, which requires heat absorption to turn into water. Understanding these reactions sheds light on natural processes and how energy is transferred in reactions.

Energy Comparison

When comparing the activation energies of exothermic and endothermic changes in a reversible reaction, it's clear they are different.
The activation energy for an exothermic reaction starts lower because it will release energy. After the initial energy input, the reaction will produce more energy than was initially put in.
On the other hand, the activation energy for an endothermic reaction is higher. This is because it needs not only to overcome the initial energy barrier but also to absorb additional energy once the reaction starts.
Therefore, in reversible reactions, the activation energy for the endothermic path is always higher. This knowledge helps in understanding the energy dynamics and is crucial for controlling reactions in industrial processes or even in everyday applications like cooking and refrigeration.