Problem 72 - Chemistry The Molecular Science

Question

Heating a metal carbonate leads to decomposition. $$ \mathrm{BaCO}_{3}(\mathrm{~s}) \rightleftharpoons \mathrm{BaO}(\mathrm{s})+\mathrm{CO}_{2}(\mathrm{~g}) $$ Predict the effect on the equilibrium of each change listed below. Answer by choosing (i) no change, (ii) shifts left, or (iii) shifts right. (Except for part (e), assume that the volume is constant.) (a) Add \(\mathrm{BaCO}_{3}\) (b) Add \(\mathrm{CO}_{2}\) (c) Add \(\mathrm{BaO}\) (d) Raise the temperature (e) Increase the volume of the reaction flask

Step-by-Step Solution

Answer

(a) No change; (b) Shifts left; (c) No change; (d) Shifts right; (e) Shifts right.

Step 1: Understanding Equilibrium

A chemical equilibrium is reached when the rate of the forward reaction equals the rate of the reverse reaction. In this dynamic state, the concentrations of reactants and products remain constant.

Step 2: Le Chatelier's Principle

Le Chatelier's Principle states that if a system at equilibrium is subjected to a change in concentration, temperature, volume, or pressure, the system will adjust itself to partially counteract the effect of the change and reach a new equilibrium.

Step 3: Analyze Effect of Adding BaCO3

Adding more solid \(\mathrm{BaCO}_{3}\) does not affect the position of the equilibrium because solids do not change ion concentrations in solution. Thus, the equilibrium position shows 'no change'.

Step 4: Analyze Effect of Adding CO2

Adding more \(\mathrm{CO}_{2}\) increases the concentration of the product, which will shift the equilibrium to the left to reestablish equilibrium according to Le Chatelier's Principle.

Step 5: Analyze Effect of Adding BaO

Adding more solid \(\mathrm{BaO}\) also does not affect the equilibrium position as solids are not part of the equilibrium expression in this context. Therefore, it results in 'no change'.

Step 6: Analyze Effect of Increasing Temperature

Since the decomposition of \(\mathrm{BaCO}_{3}\) is an endothermic process, increasing the temperature shifts the equilibrium to favor the formation of products. Thus, the equilibrium shifts to the right.

Step 7: Analyze Effect of Increasing Volume

Increasing the volume of the flask decreases the pressure, thus favoring the side with more moles of gas, i.e., the formation of \(\mathrm{CO}_{2}\). Consequently, the equilibrium shifts to the right.

Key Concepts

Le Chatelier's Principle

Le Chatelier's Principle is a fundamental idea that helps us understand how an equilibrium system responds to changes. Imagine a playground see-saw that's perfectly balanced. If you push on one side, the see-saw tilts to regain balance. Similarly, Le Chatelier's Principle states that if a disturbance is applied to a system at equilibrium, the system will adjust to counteract that disturbance and reestablish equilibrium.

Some common disturbances include changes in concentrations of reactants or products, changes in temperature, and changes in volume or pressure. When we add or remove substances, adjust temperatures, or change volumes, we are essentially "pushing" the equilibrium one way or another. The system "shifts" in the direction needed to restore balance, either by producing more products, more reactants, or adjusting their ratios to minimize the change. It's a beautiful example of nature's tendency to find balance.

Effect of Temperature on Equilibrium

Temperature changes can significantly affect a chemical equilibrium. They alter the rates of both the forward and reverse reactions, depending on whether the reaction is exothermic or endothermic. An endothermic reaction absorbs heat, similar to how an ice pack absorbs warmth from your body. Conversely, an exothermic reaction releases heat, like a warm blanket.

When the temperature increases, Le Chatelier's Principle tells us that the equilibrium will shift in a direction that absorbs extra heat. If the reaction is endothermic, increasing temperature adds energy to the system, shifting the equilibrium toward the products, as seen with the decomposition of \(\mathrm{BaCO}_{3}\) to \(\mathrm{BaO}\) and \(\mathrm{CO}_{2}\). This is because the system "favors" the endothermic direction to absorb the added heat. Conversely, lowering the temperature would favor the exothermic direction, shifting the equilibrium to the reactants.

Effect of Volume on Equilibrium

Volume changes impact equilibria involving gases because they affect pressure within the system. According to Le Chatelier's Principle, if you increase the volume of the container, the pressure decreases. Gaseous equilibria shift to the direction that produces more gas molecules to counteract this change.

In our example involving \(\mathrm{CO}_{2}\), if the container's volume increases, the system tries to increase the pressure by producing more gas molecules. As a result, the equilibrium shifts toward the side with more gaseous moles—in this case, towards the products, \(\mathrm{BaO}\) and \(\mathrm{CO}_{2}\), because of the increase in volume or decrease in pressure.

This concept is essential in industrial chemistry, where controlling pressures and volumes is necessary to optimize the production of desired chemicals.