Problem 43 - Chemistry and Chemical Reactivity

Question

The following reaction is reactant-favored at equilibrium at room temperature. $$\operatorname{COCl}_{2}(\mathrm{g}) \rightarrow \mathrm{CO}(\mathrm{g})+\mathrm{Cl}_{2}(\mathrm{g})$$ Will raising or lowering the temperature make it product-favored?

Step-by-Step Solution

Answer

Raising the temperature will make it product-favored.

Step 1: Understand the Reaction Type

The given reaction:\[ \operatorname{COCl}_{2}(\mathrm{g}) \rightarrow \mathrm{CO}(\mathrm{g}) + \mathrm{Cl}_{2}(\mathrm{g}) \]is an endothermic reaction. This means that the reaction absorbs heat from the surroundings when it proceeds from reactants to products.

Step 2: Analyze Le Chatelier's Principle

Le Chatelier's principle tells us that if a system at equilibrium is subjected to a change in temperature, the system will adjust itself to counteract that change. For endothermic reactions, increasing the temperature adds heat, shifting the equilibrium to the right (toward products), thus becoming more product-favored.

Step 3: Determine the Effect of Temperature

Since the reaction is endothermic, raising the temperature will shift the equilibrium position to favor the products. Lowering the temperature would decrease the heat available, thus making it even more reactant-favored.

Key Concepts

Endothermic Reaction

In an endothermic reaction, the system absorbs energy in the form of heat from the surroundings. Endothermic reactions require an input of energy to proceed because the products have higher energy than the reactants. For example, the reaction of carbon monoxide chloride \( \text{COCl}_2 \) breaking down into carbon monoxide \( \text{CO} \) and chlorine gas \( \text{Cl}_2 \) is endothermic. This process can be visualized as a journey uphill—requiring energy to reach the peak where products form.
Because these reactions consume heat, they are typically associated with a cooling of the surroundings where the reaction occurs. You might think of an endothermic reaction as a sponge soaking up heat, leaving the surroundings cooler.
Important characteristics of endothermic reactions include:

• Energy is absorbed.
• The enthalpy change \( \Delta H \) is positive.
• Products have greater energy than reactants.

Equilibrium

Equilibrium in chemistry occurs when the rate of the forward reaction equals the rate of the backward reaction. At this point, the concentrations of reactants and products remain constant over time. It's like achieving a delicate balance on a seesaw where neither side favours over the other.
For the reaction \( \text{COCl}_2(\mathrm{g}) \rightarrow \mathrm{CO}(\mathrm{g}) + \mathrm{Cl}_2(\mathrm{g}) \), initially, the reaction is reactant-favored at room temperature, meaning the equilibrium position is more to the left.
Understanding equilibrium involves:

• The equilibrium constant \( K \), which expresses the concentration ratio of products to reactants.
• If \( K \) is much less than 1, the reaction favors reactants.
• If \( K \) is much greater than 1, the reaction favors products.
• Any change in conditions such as temperature or pressure can shift this equilibrium position according to Le Chatelier's Principle.

Thus, knowing the position of equilibrium helps predict how a reaction will respond to changes, such as temperature modifications.

Temperature Effect

Temperature is a crucial factor affecting chemical equilibrium, especially for endothermic reactions. Le Chatelier's Principle helps us understand how systems at equilibrium respond to temperature changes. In an endothermic reaction, like the breakdown of \( \text{COCl}_2 \) into \( \text{CO} \) and \( \text{Cl}_2 \), heat can be seen as a reactant.
When the temperature increases, extra heat is added to the system. According to Le Chatelier's Principle, the system will "shift" to use up the added heat, thus shifting equilibrium toward the products. So, raising the temperature of an endothermic reaction moves the equilibrium to the right.
On the other hand, lowering the temperature reduces heat. In response, the equilibrium shifts to favor the reactants, moving left and resulting in a more reactant-favored system.
Keep in mind:

• Increasing temperature shifts equilibrium right for endothermic reactions (favoring products).
• Decreasing temperature shifts equilibrium left, reinforcing reactants.

By understanding how temperature influences reaction balance, one can predict and control the outcomes of chemical processes more effectively.