Question

State whether the following statements are true or false. If false, explain why. (a) A reaction stops when equilibrium is reached. (b) An equilibrium reaction is not affected by increasing the concentrations of products. (c) If one starts with a higher pressure of reactant, the equilibrium constant will be larger. (d) If one starts with higher concentrations of reactants, the equilibrium concentrations of the products will be larger.

Short answer

Statement (a) is false because a reaction at equilibrium continues but with no net change. Statement (b) is false as equilibrium can be affected by changes in product concentrations. Statement (c) is false; the equilibrium constant is independent of initial conditions. Statement (d) is true; higher initial concentrations of reactants tend to lead to higher equilibrium concentrations of products.

Step-by-step solution

Analyzing Statement (a)

Statement (a) is false. When a reaction reaches equilibrium, it does not stop. Rather, the rate of the forward reaction is equal to the rate of the reverse reaction, so there is no net change in the concentrations of reactants and products, although both reactions continue to occur.

Analyzing Statement (b)

Statement (b) is false. According to Le Chatelier's Principle, if the concentration of products is increased for a reaction at equilibrium, the system will shift to counteract the change, favoring the reverse reaction and thus affecting the equilibrium.

Analyzing Statement (c)

Statement (c) is false. The equilibrium constant (\( K \textsubscript{eq} \) ) for a reaction at a given temperature is constant and does not depend on the initial concentrations or pressure of reactants or products.

Analyzing Statement (d)

Statement (d) is true. Starting with higher concentrations of reactants generally leads to more products being formed until a new equilibrium is established, resulting in higher equilibrium concentrations of the products.

Key concepts

Le Chatelier's Principle

In the world of chemistry, equilibrium can be thought of as a game of tug-of-war, where both teams are evenly matched. Now, imagine if one team suddenly gets an extra player. Naturally, we would expect the team to start pulling harder, trying to restore balance. This is essentially what Le Chatelier’s Principle suggests in the realm of chemical reactions.

Therefore, when a system at equilibrium is disturbed by changing the conditions, such as pressure, temperature, or concentration of components, the system adjusts itself to counteract the effect of the disturbance and restore a new equilibrium state. For example, if the concentration of products in a balanced reaction is increased, the system will shift to favor the reaction that produces more reactants; conversely, if the pressure is increased, the system will favor the side with fewer gas molecules. This shifting helps students understand why Statement (b) from the exercise is false; the reaction is indeed affected by changing the concentrations of products.

Understanding this principle is crucial for predicting the direction in which a reaction will shift under different conditions and is an essential concept in chemical engineering, environmental science, and even pharmacology.

Equilibrium Constant

At the heart of understanding chemical equilibrium lies the equilibrium constant, denoted as \( K_{eq} \). This value is a mathematical expression representing the ratio of product concentrations to reactant concentrations at equilibrium, each raised to the power of their respective coefficients from the balanced chemical equation.

Crucially, \( K_{eq} \) is only affected by temperature; it remains unaffected by changes in concentrations or pressure. This is why Statement (c) is false; starting with a higher pressure of reactant will not affect the value of \( K_{eq} \). The constant nature of \( K_{eq} \) gives us a predictable way to calculate the position of equilibrium and understand chemical processes, which is fundamental for industries that synthesize chemical compounds.

Moreover, if we know the equilibrium constant for a particular reaction at a given temperature, we can predict whether the reactants or products are favored in an equilibrium state. A larger \( K_{eq} \) suggests products are favored; a smaller \( K_{eq} \) suggests reactants are favored.

Reaction Rates

The rate of a chemical reaction tells us how quickly reactants are transformed into products. It's important to understand that reaching chemical equilibrium does not imply that reactions have ceased. Instead, as described in Statement (a), equilibrium is achieved when the rates of the forward and reverse reactions are equal, resulting in no net change in the concentrations of reactants and products over time.

The exciting part about reaction rates is that they are influenced by several factors, including the concentration of reactants, temperature, surface area, and the presence of catalysts. An increase in the concentration of reactants usually leads to an increase in the reaction rate because there are more particles that can collide and react with each other.

However, as equilibrium is established, the reaction rate of the forward process and that of the reverse process become the same, creating a dynamic but balanced system. This understanding helps to clarify why Statement (d) is true. Starting with higher concentrations of reactants shifts the equilibrium position and may lead to increased production of products until the new equilibrium is achieved.