Question

True or false? The position of a heterogeneous equilibrium does not depend on the amounts of pure solid or pure liquid reactants or products present because the concentrations of pure solids and liquids cannot change. True False

Short answer

True. The position of a heterogeneous equilibrium does not depend on the amounts of pure solid or pure liquid reactants or products present because the concentrations of pure solids and liquids cannot change.

Step-by-step solution

Consider Heterogeneous Equilibria in a reaction

A heterogeneous equilibrium involves a chemical reaction where the reactants and products are in different phases (such as solid, liquid, and gas). The position of equilibrium for such reactions can be expressed in terms of the equilibrium constant (K) involving concentrations of reactants and products in a gaseous or dissolved species. Pure solids and liquids have a constant concentration because their density does not change with the amount.

The effect of the presence of pure solids and liquids on equilibrium position

According to Le Chatelier's principle, the position of equilibrium will shift to minimize the impact of any changes in the system. However, adding or removing a pure solid or liquid will not affect the position of a heterogeneous equilibrium, because their concentrations remain constant, and therefore, the equilibrium constant (K) will not change. So, the position of equilibrium does not depend on their amounts in the reaction system.

Conclusion on the statement

Based on the understanding of heterogeneous equilibria and the effect of pure solids or liquids on the position of equilibrium, the given statement is True. The position of a heterogeneous equilibrium does not depend on the amounts of pure solid or pure liquid reactants or products present because the concentrations of pure solids and liquids cannot change.

Key concepts

Equilibrium Constant

The equilibrium constant, often represented as \( K \), is a crucial concept in understanding chemical reactions where substances do not change phases. It is a constant value that allows us to predict the extent of a reaction at equilibrium, based on the concentrations of reactants and products. In a chemical equation:\[ aA + bB \rightleftharpoons cC + dD \]The equilibrium constant expression \( K \) is typically given by:\[ K = \frac{{[C]^c [D]^d}}{{[A]^a [B]^b}} \]The equilibrium constant is only applicable to reactions involving gases or solutes, as the concentrations of pure solids and liquids remain steady.

• Gases and Dissolved Substances: Their concentrations change during the reaction, so they appear in the \( K \) expression.
• Pure Solids and Liquids: Their concentrations are constant, as these are unchanging physical properties such as density. Therefore, they are excluded from the \( K \) expression.

This behavior highlights why the equilibrium position of a heterogeneous reaction remains unaffected by the amount of pure solid or liquid present.

Le Chatelier's Principle

Le Chatelier's Principle is a fundamental theory that explains how a reaction at equilibrium responds to changes in concentration, pressure, or temperature. It states that if an equilibrium system is disturbed, the reaction will adjust itself to counteract the disturbance and restore a new equilibrium.

• Concentration Changes: Adding or removing reactants or products will shift the equilibrium to offset the change.
• Pressure and Volume Changes: In reactions involving gases, changes in pressure or volume can shift the equilibrium towards the side with fewer or more moles of gas.
• Temperature Changes: Increasing temperature favors endothermic reactions, while decreasing temperature favors exothermic ones.

For heterogeneous equilibria, changing the amount of pure solids or liquids does not alter the equilibrium position. This is because their concentrations do not vary. Thus, even with changes in their amount, their impact on equilibrium remains neutral, aligning with the principle that the system resists such disturbances.

Pure Substances in Equilibrium

Pure substances such as solids and liquids play a unique role in equilibrium reactions. Their concentrations are seen as constants because they are inherent properties (like density) and don't fluctuate with quantity in the system.In heterogeneous equilibria, these constant concentrations of solids and liquids simplify the expression of the equilibrium constant. Since they do not appear in the \( K \) expression, the amount of pure solid or liquid will not influence the equilibrium state.Some key points include:

• Pure Solids: Take, for example, calcium carbonate (CaCO₃) in a decomposition reaction. Like other pure solids, its concentration does not change, regardless of the amount present.
• Pure Liquids: Water often acts as a solvent but in reactions where it is a reactant or product in its liquid form, it is not included in the equilibrium expression.

This concept is significant because it underscores why adding or removing pure substances doesn’t affect a heterogeneous equilibrium’s position. Thus, these substances maintain consistency in the expression and calculation of equilibrium constants.