The equilibrium constant for the formation of phosphorus pentachloride is 1.9. If the partial pressure of each gas is 0.5 atm, will the reaction (as written) proceed forward or backward to reach equilibrium?
PCl3(g) + Cl2(g) PCl5(g)
A. Backward, because K is greater than Q
B. Backward, because K is less than Q
C. Forward, because K is less than Q
D. Forward, because K is greater than Q
I know that this is either B or D, but am not sure which. Can you help me please?
its B. Q=0.5/0.5^2=2
K=1.9
Q>K so reverse reaction
Q=.5
K=1.9
K>Q
shifts right.
http://chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Equilibria/Chemical_Equilibria/The_Reaction_Quotient/Difference_Between_K_And_Qhttp://chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Equilibria/Chemical_Equilibria/The_Reaction_Quotient/Difference_Between_K_And_Q
the answer was B? K<Q
Hmmmm. We are on different planets.
To determine whether the reaction will proceed forward or backward to reach equilibrium, we need to compare the reaction quotient (Q) to the equilibrium constant (K).
The reaction quotient (Q) is calculated using the same formula as the equilibrium constant (K), but with the concentrations or partial pressures of the reactants and products at any given point in the reaction.
In this case, the reaction can be represented as:
PCl3(g) + Cl2(g) ⇌ PCl5(g)
The equilibrium constant (K) is given as 1.9.
When the reaction is at equilibrium, the reaction quotient (Q) is equal to the equilibrium constant (K). In this scenario, with partial pressures of each gas at 0.5 atm, we need to calculate Q.
Q = (PCl5)/[(PCl3)(Cl2)]
Since the partial pressures of each gas are given as 0.5 atm, we can substitute these values:
Q = (0.5) / [(0.5)(0.5)] = 2
Comparing Q and K, we find that Q (2) is greater than K (1.9). This implies that the reaction has not yet reached equilibrium.
According to Le Chatelier's principle, if Q is greater than K, the reaction will shift in the reverse direction to reach equilibrium. Therefore, the answer is:
B. Backward, because K is less than Q