Problem 39 - Chemistry and Chemical Reactivity

Question

Heating a metal carbonate leads to decomposition. $$ \mathrm{BaCO}_{3}(\mathrm{s}) \rightleftarrows \mathrm{BaO}(\mathrm{s})+\mathrm{CO}_{2}(\mathrm{g}) $$ 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 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) shifts right, (b) shifts left, (c) shifts left, (d) shifts right, (e) shifts right.

Step 1: Understanding the Reaction

The given chemical equation is reversible. The equilibrium position is determined by Le Chatelier's principle, which states that if a change in condition is applied to a reversible reaction at equilibrium, the system adjusts to counteract that change and establish a new equilibrium.

Step 2: Add BaCO3

Adding more BaCO\(_3\) increases the concentration of reactants. By Le Chatelier's principle, to counteract this increase, the equilibrium will shift to the right to produce more products.

Step 3: Add BaO

Adding BaO increases the concentration of one of the products. To counteract this increase, the equilibrium will shift to the left, favoring the formation of BaCO\(_3\) and reducing CO\(_2\).

Step 4: Add CO2

Adding CO\(_2\) increases the concentration of this gaseous product. Thus, the equilibrium shifts to the left in order to decrease the concentration of CO\(_2\), increasing the formation of BaCO\(_3\).

Step 5: Raise the Temperature

Since this is a decomposition reaction, it is typically endothermic (absorbs heat). Increasing the temperature provides more energy, favoring the endothermic direction, which in this case is to the right, producing more BaO and CO\(_2\).

Step 6: Increase Volume of the Flask

Increasing the volume decreases the pressure. For reactions involving gases, the equilibrium shifts towards the side with more moles of gas. Here, increasing the volume will shift the equilibrium to the right, as it results in more moles of gas due to the production of CO\(_2\).

Key Concepts

Chemical Equilibrium

Chemical equilibrium occurs in reversible reactions when the rate of the forward reaction equals the rate of the reverse reaction. At this point, the concentrations of reactants and products remain constant. This doesn't mean that the amounts are equal, just that they have settled into a steady balance.
Le Chatelier's Principle plays a crucial role in understanding how equilibria react to changes. It states that if a change is applied to a system at equilibrium, the system will adjust itself to partially counteract the change and establish a new equilibrium. For instance, altering the concentration of products or reactants can cause the reaction to shift, moving in the direction that opposes the change.

• Adding reactants tends to shift equilibrium towards the products.
• Adding products usually pushes the equilibrium towards the reactants.

These shifts help restore balance by either producing more reactants or more products as needed.

Decomposition Reaction

Decomposition reactions involve the breaking down of a single compound into two or more simpler substances. In the exercise provided, barium carbonate (\( \text{BaCO}_3 \)) decomposes into barium oxide (\( \text{BaO} \)) and carbon dioxide (\( \text{CO}_2 \)) upon heating.
This reaction is typical of many metal carbonates decomposing under heat, where we see:
\[\text{BaCO}_3(s) \rightleftharpoons \text{BaO}(s) + \text{CO}_2(g)\]
Decomposition reactions often require energy in the form of heat, and they can be endothermic. As they progress, they reach a state of equilibrium where the rate of decomposition equals the rate of formation of the reactants. The behavior of such reactions is well studied using Le Chatelier’s Principle, predicting how adding or removing substances or heat affects the equilibrium balance. This scientific principle helps us manage and control these reactions in various practical applications.

Reaction Shifts

In chemical reactions, especially those at equilibrium, the system can adjust in response to several factors. This adjustment is often referred to as a 'shift' in equilibrium. Remember, these shifts are defensive moves from the reaction to stay balanced.
Common causes for a reaction shift include changes in:

• Concentration: Adding reactants or products can cause the system to shift to offset the change, as seen with the addition of \( \text{CO}_2 \) which shifts the equilibrium to the left.
• Temperature: In endothermic reactions like the decomposition of \( \text{BaCO}_3 \), increasing temperature shifts the equilibrium to the right, favoring more product formation.
• Pressure or volume: Changing the volume of gases affects equilibrium. For example, increasing volume decreases pressure, shifting the reaction toward the side with more gas moles, such as moving right in the original reaction.

Understanding these variables and their influence gives us insights into controlling chemical processes, making it possible to predict and manage the outcomes more effectively.