Question

The equilibrium constant of a reversible chemical reaction at a given temperature (1) depends on the initial concentration of the reactants (2) depends on the concentration of onc of the products at cquilibrium (3) does not depend on the initial concentration of feactants (4) is not characteristic of the reaction

Short answer

Option (3) is correct: The equilibrium constant does not depend on the initial concentration of reactants.

Step-by-step solution

Understanding Equilibrium Constant

The equilibrium constant, denoted as K, is a measure of the ratio of product concentrations to reactant concentrations at equilibrium for a reversible chemical reaction. It is specific to a given reaction at a given temperature.

Reviewing Initial Concentrations

Consider the initial concentrations of reactants in the reaction. The equilibrium constant K is defined only at equilibrium and does not depend on initial concentrations of reactants.

Analyzing Equilibrium Concentrations

At equilibrium, the reaction has reached a state where the forward and reverse reaction rates are equal. K is calculated using the concentrations of both reactants and products at this equilibrium state.

Evaluating Each Answer Option

1. Incorrect: K does not depend on initial concentrations of reactants.2. Incorrect: K is dependent on the concentrations of both reactants and products at equilibrium, not just one product.3. Correct: K does not depend on the initial concentration of reactants.4. Incorrect: K is characteristic of the reaction and is a constant for each specific reaction at a given temperature.

Conclusion

The equilibrium constant is specific to the reaction and is not influenced by the initial concentrations of reactants but rather by the ratio of products to reactants at equilibrium.

Key concepts

equilibrium constant definition

Understanding the equilibrium constant is essential for grasping chemical equilibrium. The equilibrium constant, represented by K, quantifies the ratio of the concentrations of products to reactants at equilibrium in a reversible reaction. It uniquely represents this specific state for each chemical reaction at a specified temperature. The mathematical formula is given by:
\[ K = \frac{[Products]}{[Reactants]} \]
where the concentrations are measured in terms of their molarity. It’s important to remember that these concentrations are taken when the reaction has reached equilibrium.

dependence on reactant concentrations

A common misconception is that the equilibrium constant depends on the initial concentrations of the reactants. However, this is not correct. The initial concentrations do not affect the value of K. Instead, K is determined by the concentrations of reactants and products once the reaction reaches equilibrium.
Here’s why: regardless of where a reaction starts (initial concentrations), it will eventually settle at a specific point where the rates of the forward and reverse reactions balance each other. This point is equilibrium, and K reflects the ratio at this state.
Thus, whether you start with more reactants or more products, if you wait long enough, the system will adjust to maintain the equilibrium constant.

relationship at equilibrium

At equilibrium, the rate of the forward reaction equals the rate of the reverse reaction. This balance means no net change in the concentrations of reactants and products occurs. To better understand this:

• The forward reaction converts reactants to products.
• The reverse reaction converts products back to reactants.

This continual yet balanced conversion defines equilibrium.
The equilibrium constant (K) uses the concentrations of both reactants and products measured at this equilibrium stage. This relationship ensures K remains constant for a given reaction under constant temperature.

temperature specificity

Temperature significantly impacts the equilibrium constant. Each reaction has an equilibrium constant that is specific to a particular temperature. If you change the temperature, you change the value of K for that reaction.
Here's how temperature affects K:

• For endothermic reactions (heat-absorbing), increasing temperature increases K.
• For exothermic reactions (heat-releasing), increasing temperature decreases K.

Understanding this dependency is crucial as it shows that K is not a static value but varies with temperature changes. Therefore, while the equilibrium constant is unique for each reaction, it only holds true at a certain temperature.