Problem 41 - Chemistry and Chemical Reactivity

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. (a) add \(\mathrm{BaCO}_{3}\) (c) add BaO (b) add \(\mathrm{CO}_{2}\) (d) raise the temperature (e) increase the volume of the flask containing the reaction

Step-by-Step Solution

Answer

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

Step 1: Understand the Equilibrium Reaction

The reaction given is \( \mathrm{BaCO}_3(\mathrm{s}) \rightleftharpoons \mathrm{BaO}(\mathrm{s}) + \mathrm{CO}_2(\mathrm{g}) \). In equilibrium reactions, changes in conditions can shift the equilibrium position either to the left or right according to Le Chatelier's principle.

Step 2: Adding \(\mathrm{BaCO}_3\)

Since \(\mathrm{BaCO}_3\) is a solid, adding more of it does not affect the equilibrium position. Solids do not appear in the equilibrium expression, so the equilibrium position will not change.

Step 3: Adding \(\mathrm{BaO}\)

As \(\mathrm{BaO}\) is also a solid, adding more \(\mathrm{BaO}\) will not affect the equilibrium position. Solids are not part of the equilibrium expression, leading to no change in equilibrium.

Step 4: Adding \(\mathrm{CO}_2\) Gas

Adding more \(\mathrm{CO}_2\), a gaseous product, will increase its concentration. According to Le Chatelier's principle, the equilibrium will shift left to reduce the additional \(\mathrm{CO}_2\) and re-establish equilibrium.

Step 5: Raising the Temperature

Decomposition of \(\mathrm{BaCO}_3\) is an endothermic process. Raising the temperature will favor the endothermic forward reaction, causing the equilibrium to shift right and produce more \(\mathrm{BaO}\) and \(\mathrm{CO}_2\).

Step 6: Increasing the Volume of the Flask

Increasing the volume of the container decreases the pressure, favoring the side with more gas moles. Since only \(\mathrm{CO}_2\) is a gas, the equilibrium will shift right to produce more \(\mathrm{CO}_2\) to counteract the decrease in pressure.

Key Concepts

Chemical Equilibrium

Chemical equilibrium occurs when the forward and reverse reactions in a chemical process occur at the same rate, making the concentrations of reactants and products constant. This does not mean the amounts are equal, just that they do not change over time. Different factors can affect a chemical equilibrium, and Le Chatelier's Principle helps predict how the system will adjust when these factors change. For example, adding more of a gaseous product will cause the system to shift in a direction that opposes the change.

Endothermic Reactions

Endothermic reactions absorb energy from the surroundings, often in the form of heat. In the case of our chemical reaction, decomposing Barium carbonate (\( \mathrm{BaCO}_3 \)) into barium oxide (\( \mathrm{BaO} \)) and carbon dioxide (\( \mathrm{CO}_2 \)) is an endothermic process. This means that increasing the temperature provides more energy for the reaction to proceed towards producing more \( \mathrm{BaO} \) and \( \mathrm{CO}_2 \). The equilibrium will shift in the direction that absorbs heat, meaning it favors the formation of products under high-temperature conditions.

Effects of Pressure

In reactions involving gases, pressure can be a key factor influencing equilibrium. For reactions with different numbers of gas molecules on either side, such as our reaction where only \( \mathrm{CO}_2 \) is a gas, increasing the volume of the container decreases the pressure.

• This decrease in pressure will cause the equilibrium to shift towards the side with more moles of gas, producing more \( \mathrm{CO}_2 \).
• If the pressure increases by reducing the container size, the equilibrium will shift towards fewer gas moles, potentially favoring the formation of \( \mathrm{BaCO}_3 \).

Understanding these dynamics helps in controlling chemical reactions, especially in industrial processes.

Gas Concentration in Reactions

The concentration of gases in a reaction directly affects the equilibrium position. Adding more \( \mathrm{CO}_2 \), as highlighted in this example, increases its concentration in the reaction mixture. According to Le Chatelier's Principle, the system will respond by shifting the equilibrium to reduce the concentration of this added gas.

• This shift will be towards the left, forming more \( \mathrm{BaCO}_3 \).
• The opposite occurs if \( \mathrm{CO}_2 \) is removed, causing the equilibrium to shift right to produce more gas until equilibrium is restored.

This fundamental understanding of gas concentration effects ensures better manipulation of product outcomes in chemical reactions.