Consider the equilibrium
CO(g)+3H₂( g)⇌ CH₄( g)+H₂O( g)
If the pressure applied over the system increases by two fold at constant temperature then
(A) Concentration of reactants and products increases.
(B) Equilibrium will shift in forward direction.
(C) Equilibrium constant increases since concentration of products increases.
(D) Equilibrium constant remains unchanged as concentration of reactants and products remain same.
Choose the correct answer from the options given below :

Solution

Chemistry ma’am · 4 steps

Squeezing the gases raises every concentration, but only temperature can change K.

1. What doubling does. Doubling the pressure at constant temperature means halving the volume. At that instant every concentration doubles, for reactants and products alike.
2. Which way it shifts. The left side has 1 + 3 = 4 moles of gas and the right side has 1 + 1 = 2. The system relieves the extra pressure by moving towards fewer gas moles, so it shifts forward.

   Q_c = (2)(2)/(2)(2)³ K_c = K_c/4 < K_c

3. Check each statement. The shift only partly undoes the change, so concentrations end up higher than before the compression. K_c depends only on temperature, so it stays the same.

   Statement	Verdict	Reason
   (A) Concentrations increase	True	Halving the volume crowds the same moles into less space
   (B) Shifts forward	True	4 gas moles go to 2 gas moles
   (C) K increases	False	Temperature is constant, so K is fixed
   (D) K unchanged because concentrations stay the same	False	K is unchanged, but the concentrations do change

4. So. Only (A) and (B) are correct, which is option (a).

The idea to keep. A pressure change moves the position of equilibrium towards fewer gas moles, but K only moves when temperature does. Judge a statement by its reason as well as its conclusion.

Answer from the NTA final answer key. Solution by PrepWiser.