Question

For a chemical reaction A $\rightleftharpoons$ B, the necessary conditions for the state of equilibrium is/are,
A. \(C_{A}=C_{B}\)
B. \(\mu_{A}=\mu_{B}\)
C. \(P_{A}=P_{B}\)
D. \(G_{A}=G_{B}\)
E. \(H_{A}=H_{B}\)
Choose the correct answer from the options given below:

• A. A and C Only
• B. B and D Only
• C. D and E Only
• D. E Only

Hint:

Concentration does NOT have to be equal at equilibrium! Equilibrium is about energy balance (\(\mu\) and \(G\)), not a physical amount balance.

Answer 1

The Correct Option is B

Concept: Chemical equilibrium is reached when the driving forces for the forward and backward reactions are perfectly balanced. Thermodynamically, this is defined by the chemical potential and Gibbs free energy.

Step 1: Evaluate thermodynamic equilibrium criteria.

• Statement B: Correct. At equilibrium, the chemical potential (\(\mu\)) of every component must be the same in all phases and for all reaction states.
• Statement D: Correct. For a reaction at constant temperature and pressure, equilibrium is achieved when the total Gibbs free energy ($G$) is at its minimum, and the change in Gibbs free energy (\(\Delta G\)) is zero.
• Other statements: Equilibrium does not mean concentrations ($C$), pressures ($P$), or enthalpies ($H$) are equal; it only means their rates of change are zero.