Question

The reaction $$\mathrm{C}_{2} \mathrm{H}_{2}(g)+2 \mathrm{Br}_{2}(g) \rightleftharpoons \mathrm{C}_{2} \mathrm{H}_{2} \mathrm{Br}_{4}(g)$$ is exothermic in the forward direction. Will an increase in temperature shift the position of the equilibrium toward reactants or products?

Short answer

An increase in temperature will shift the position of the equilibrium towards the reactants in the given exothermic reaction \(\mathrm{C}_{2} \mathrm{H}_{2}(g) + 2 \mathrm{Br}_{2}(g) \rightleftharpoons \mathrm{C}_{2} \mathrm{H}_{2} \mathrm{Br}_{4}(g)\) according to Le Chatelier's Principle, as the reverse reaction is endothermic and will absorb the added heat.

Step-by-step solution

1. Identify the exothermic reaction

The given reaction is: \(\mathrm{C}_{2} \mathrm{H}_{2}(g)+2 \mathrm{Br}_{2}(g) \rightleftharpoons \mathrm{C}_{2} \mathrm{H}_{2} \mathrm{Br}_{4}(g)\) As mentioned, this reaction is exothermic in the forward direction. That means it releases heat when the reaction proceeds from left (reactants) to right (products).

2. Apply Le Chatelier's Principle

According to Le Chatelier's Principle, increasing the temperature will cause the equilibrium to shift in the direction that absorbs the added heat. Since the forward reaction is exothermic (releases heat), the reverse reaction must be endothermic (absorbs heat).

3. Determine the effect of increasing temperature on the equilibrium position

Based on Le Chatelier's Principle, when we increase the temperature, the equilibrium will shift to counteract the change. In this case, it will shift in the endothermic direction (the reverse direction) to absorb the added heat. This means that the equilibrium will shift towards the reactants. In conclusion, an increase in temperature will shift the position of the equilibrium towards the reactants in this exothermic reaction.

Key concepts

Chemical Equilibrium

Imagine a busy downtown street where cars, bicycles, and pedestrians are moving back and forth continuously. Now, picture this traffic flowing in such a way that, over time, the number of entities going in each direction is equal. The system is 'balanced' even though there's constant movement. This analogy helps us understand chemical equilibrium, which occurs in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction, and the concentrations of reactants and products remain constant.

At this point, it's important to note that chemical equilibrium does not mean that reactants and products are present in equal amounts but rather that their ratios do not change over time. The position of equilibrium may favor the reactants, the products, or be somewhere in between, depending on various factors such as temperature, pressure, and concentration changes.

Exothermic Reactions

Let's warm up with a look at exothermic reactions. Have you ever watched a campfire crackle and felt the warmth on your face? That's an everyday example of an exothermic reaction, where energy, typically in the form of heat, is released into the surrounding environment. In chemical terms, this means the energy required to break the bonds of the reactants is less than the energy released when new bonds form in the products.

During such a reaction, you'll notice that products have less energy compared to the reactants, a phenomenon that is often associated with increased stability. Examples of exothermic reactions include combustion of fuels, rusting of iron, and many metabolic processes in living organisms.

Endothermic Reactions

On the flip side, we have endothermic reactions, which are kind of like a chemical refrigerator. These reactions absorb energy from their surroundings, typically in the form of heat. Imagine you're baking bread, and the dough rises because of yeast fermentation - that's energy being consumed to drive an endothermic process.

In these reactions, the energy needed to break bonds in the reactants is greater than the energy released when new bonds are formed in the products. Consequently, the overall process requires an input of energy, resulting in a cooler environment around the reaction mixture. Endothermic processes can be found in photosynthesis, evaporation, and the cooking of certain foods.

Equilibrium Shift on Temperature Change

When you tweak the temperature in a room, what happens? If it's too hot, the air conditioner kicks in to cool things down. This is similar to how Le Chatelier's Principle explains what happens to a chemical system at equilibrium when subjected to a temperature change. If an exothermic reaction is in equilibrium and the temperature increases, the system will respond by 'turning on the air conditioner' and shifting the equilibrium to favor the absorption of heat, which is characteristic of the endothermic backward reaction.

In contrast, if the equilibrium involves an endothermic reaction and the surroundings get colder, the system would 'light a fire' by shifting the equilibrium towards the heat-releasing exothermic direction. Understanding this principle assists chemists in optimizing conditions for various industrial processes to ensure the maximum yield of products.