Reaction Quotient

Reaction Quotient

Reaction Quotient

Reaction Quotient(Q)

Reaction quotient is a measure of the relative amounts of products and reactants present in a reaction at a particular point of time.
For reversible reaction
aA + bB ⇌ cC + dD
where a, b, c and d are the stoichiometric coefficients for the balanced reaction, we can calculate reaction quotient using the following equation-
Q = [C]c [D]d / [A]a [B]b
Reaction quotient applied at any stage of reaction but Equilibrium constant only at equilibrium.
Reaction quotient(Q) can predict the direction of reaction by comparing with equilibrium constant(K).
1. When Q = K, then reaction is in equilibrium state.
2. When Q < K the concentration of the reactants is higher than it would be at equilibrium. In order to reach equilibrium, the reaction will favor the forward reaction. So, the rate of forward reaction increases.
3. When Q > K the concentration of the products is higher than it would be at equilibrium. In order to reach equilibrium, the reaction will favor the backward reaction. So, the rate of backward reaction increases.
If the value of Q is ≥ 103, Product predominates
If the value of Q is ≤ 10-3, Reactant predominates
If the value of Q is in between 10-3 to 103, significant amounts of both products and reactants

The value of the reaction quotient Q, for the cell
Zn(s)∣Zn2+(0.01 M) ∥ Ag+(1.25 M)∣Ag(s) is

1. 156
2. 125
3. 1.25 x 10-2
4. 6.4 x 10-3

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