Question

Consider the following equilibrium \(A(g) + B(g) \rightleftharpoons C(g) + D(g)\). The equilibrium constant will be altered when

• A. reactant ‘A’ is added to the system at constant temperature
• B. product ‘D’ is added to the system at constant temperature
• C. total pressure is changed at constant temperature
• D. both ‘A’ and ‘D’ are added to the system at constant temperature
• E. change in temperature.

Hint:

Remember: "Equilibrium position shifts with many factors, but the equilibrium constant shifts only with temperature." This is a fundamental rule in chemical kinetics and thermodynamics.

Answer 1

Answer: (E)

Step 1: Understanding the Concept:
The equilibrium constant (\(K_c\) or \(K_p\)) is a characteristic property of a chemical reaction at a specific temperature. According to thermodynamic principles, the value of the equilibrium constant is independent of the concentrations of reactants and products, the presence of a catalyst, or changes in total pressure.

Step 2: Detailed Explanation:
1. Concentration Changes: Adding or removing reactants (like ‘A’) or products (like ‘D’) will shift the equilibrium position according to Le Chatelier’s Principle to maintain the ratio, but the numerical value of \(K\) remains the same as long as the temperature is constant.
2. Pressure Changes: For a gas-phase reaction, changing the total pressure might shift the equilibrium if there is a difference in the number of moles of gas, but the constant \(K\) does not change.
3. Temperature Changes: The equilibrium constant is related to the standard Gibbs free energy change by the equation \(\Delta G^\circ = -RT \ln K\). Since \(\Delta G^\circ\) and \(T\) are intrinsic to the constant's definition, any change in temperature (\(T\)) will result in a new value for \(K\).

Step 3: Final Answer:
The equilibrium constant is altered only by a change in temperature.