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At 850 K the equilibrium constant for the following reaction is Kc=15
2SO2(g) + O2(g) ⇋ 2SO3(g)
If we mix the following concentrations of the three gases, predict in which direction the net reaction will proceed toward equilibrium: Left, No Change, or Right.
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Q is the reaction’s quotient. ( Q) is the quantity of reactants relative to the products during a specific moment in time. Similarly the equilibrium constant ( K) is the the ratio of products to reactants at the point of reaching equilibrium. Q is the measure of reaction at different times and is used to predict the final direction that the reaction’s progress in order to reach equilibrium.
Reaction quotient Q = [SO3]2 / ([SO2]2[O2])
If Q > Kc, the reaction will be weighted by products and the reaction proceeds in a direction backwards towards the reactants until it reaches equilibrium.
If Q < Kc, then the reaction is weighted by reactants and the reaction will continue in a forward direction toward the equilibrium point of the product.
Given:
Kc = 15
Part (a)
Q = [SO3]2 / ([SO2]2[O2]) = (0.60)2 / ((0.20)2(0.60)) = 15
As Q = Kc, the reaction is already in equilibrium. Therefore, there is no change.
Part (b)
Q = [SO3]2 / ([SO2]2[O2]) = (0.14)2 / ((0.70)2(0.70)) =0.057
As Q < Kc, the reaction will proceed in the direction of forward (Right).
Part (c)
Q = [SO3]2 / ([SO2]2[O2])= (0.50)2 / ((0.20)2(0.10)) =62
As Q > Kc, the reaction will continue in the reverse in the direction of (Left).