A sealed vessel at 298 K contains the gaseous reaction A(g) + 2 B(g) ⇌ C(g) + D(g)…
CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
A sealed vessel at 298 K contains the gaseous reaction
A(g) + 2 B(g) ⇌ C(g) + D(g)
Initially the system is at equilibrium. A technician then injects a pulse of pure B, instantaneously doubling the partial pressure of B while the other species remain unchanged at that moment.
(a) Write the expression for the reaction quotient immediately after the injection in terms of the partial pressures of all four species.
(b) State whether the value of the reaction quotient right after the injection is less than, equal to, or greater than the equilibrium constant, and explain your reasoning without performing a numerical calculation.
(c) Predict the direction in which the net reaction will proceed to re-establish equilibrium. Indicate the sign of ΔG for the forward direction at the instant immediately following the injection.
(d) Provide a thermodynamic justification that links the relative values of Q and K to the sign of ΔG in this situation.