Question

This reaction is endothermic. $$ \mathrm{C}_{2} \mathrm{H}_{4}(g)+\mathrm{I}_{2}(g) \rightleftharpoons \mathrm{C}_{2} \mathrm{H}_{4} \mathrm{I}_{2}(g) $$ If you were a chemist trying to maximize the amount of \(\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{I}_{2}\) produced, which of the following might you try? Assume that the reaction mixture reaches equilibrium. (a) decreasing the reaction volume (b) removing \(\mathrm{I}_{2}\) from the reaction mixture (c) raising the reaction temperature (d) adding \(\mathrm{C}_{2} \mathrm{H}_{4}\) to the reaction mixture

Short answer

To maximize the production of \(\mathrm{C}_{2}\mathrm{H}_{4}\mathrm{I}_{2}\), the best options are to raise the reaction temperature (c) and add more \(\mathrm{C}_{2}\mathrm{H}_{4}\) to the mixture (d).

Step-by-step solution

Understand the Nature of the Reaction

Recognize that the reaction is endothermic, which means it absorbs heat. According to Le Chatelier's Principle, increasing temperature will shift the equilibrium position in the direction that absorbs heat to counteract the change; thus, increasing the temperature will favor the formation of products in an endothermic reaction.

Assess the Impact of Decreasing Reaction Volume

Decreasing the reaction volume increases the pressure. For reactions involving gases, the direction of the shift at equilibrium will favor the side with fewer moles of gas. However, since both sides of the reaction have the same number of moles of gas, changing the volume will not affect the equilibrium in production of the desired product.

Consider the Effect of Removing I2 from the Mixture

Removing one of the reactants, like \(\mathrm{I}_{2}\), from the reaction mixture shifts the equilibrium towards the reactants in order to increase the concentration of \(\mathrm{I}_{2}\) back towards equilibrium. This would decrease the amount of \(\mathrm{C}_{2}\mathrm{H}_{4}\mathrm{I}_{2}\) produced.

Effects of Adding C2H4 to the Reaction Mixture

Adding more of the reactant \(\mathrm{C}_{2}\mathrm{H}_{4}\) will shift the equilibrium toward the products to counteract the increase in concentration of the reactant. This action can increase the amount of \(\mathrm{C}_{2}\mathrm{H}_{4}\mathrm{I}_{2}\) produced.

Analyze the Options Based on Le Chatelier's Principle

Now analyze each option given:(a) Decreasing the reaction volume does not shift equilibrium in either direction in this case.(b) Removing \(\mathrm{I}_{2}\) would decrease the production of \(\mathrm{C}_{2}\mathrm{H}_{4}\mathrm{I}_{2}\).(c) Raising the reaction temperature would shift the equilibrium towards the products, thus increasing the yield of \(\mathrm{C}_{2}\mathrm{H}_{4}\mathrm{I}_{2}\) because the reaction is endothermic.(d) Adding more \(\mathrm{C}_{2}\mathrm{H}_{4}\) would also shift the equilibrium towards products and increase the amount of \(\mathrm{C}_{2}\mathrm{H}_{4}\mathrm{I}_{2}\) produced.

Key concepts

Le Chatelier's Principle

Understanding Le Chatelier's Principle is fundamental when you're trying to manipulate a chemical reaction to favor the production of a desired product. This principle states that if an external change is applied to a system at equilibrium, the system will adjust to partially counteract the change and a new equilibrium will be established.

For instance, if you increase the concentration of reactants in a balanced reaction, the system will respond by converting some of the added reactants into products, thereby increasing the yield of the desired compound. Similarly, if the pressure of a gaseous reaction is increased by decreasing volume, and if one side has fewer moles of gas, the system will shift towards that side to reduce pressure. However, in the reaction with equal moles on both sides, this change wouldn't make a difference in the equilibrium position.

Chemical Equilibrium

Chemical equilibrium is achieved when the rates of the forward and reverse reactions are equal, leading to no net change in the concentration of reactants and products over time. It's important to recognize that equilibrium does not mean the reactants and products are present in equal amounts, but rather that their ratios do not change.

When working with chemical equilibrium, it's crucial to realize that changes in concentration, pressure, and temperature can all have significant impacts on the position of equilibrium. Equilibrium can be dynamic, meaning that reactants and products are still being formed and consumed, but the macroscopic properties remain constant. Understanding equilibrium helps chemists determine the best conditions to optimize the yield of a reaction.

Reaction Temperature Effects

The effect of temperature on the equilibrium of a chemical reaction is particularly interesting when dealing with endothermic and exothermic reactions. For an endothermic reaction, which absorbs energy from the surroundings, an increase in temperature drives the equilibrium forward, towards the products. This is because the extra heat added acts as a reactant, according to Le Chatelier's Principle.

In contrast, for an exothermic reaction, which releases energy, raising the temperature will shift the equilibrium towards the reactants. It's vital for chemists to control the temperature to either increase the yield of the desired product or to prevent unwanted products from forming in temperature-sensitive reactions.