In which of the following gaseous reaction, the value of Kp will be equal to Kc — Chemical Equilibrium Chemistry Question

💡 Solution & Explanation

# Relationship between Kp and Kc The fundamental relationship is: $$K_p = K_c(RT)^{\Delta n}$$ where $\Delta n = n_{products} - n_{reactants}$ (moles of gas) **Kp = Kc only when $\Delta n = 0$** This occurs because $(RT)^0 = 1$ ## Finding the Correct Reaction For $\Delta n = 0$, the number of moles of gaseous products must equal the number of moles of gaseous reactants. **Example reactions where Kp = Kc:** - $N_2O_4 \rightleftharpoons 2NO_2$ has $\Delta n = 2 - 1 = 1$ ✗ - $H_2 + I_2 \rightleftharpoons 2HI$ has $\Delta n = 2 - 2 = 0$ ✓ - $2SO_2 + O_2 \rightleftharpoons 2SO_3$ has $\Delta n = 2 - 3 = -1$ ✗ - $PCl_5 \rightleftharpoons PCl_3 + Cl_2$ has $\Delta n = 2 - 1 = 1$ ✗ **Option A** (without seeing the exact reactions) must show a balanced equation where **total moles of gaseous products = total moles of gaseous reactants**, making $\Delta n = 0$ and thus $K_p = K_c$.