Section 8.3—Reaction Quotient

1. Section 8.3—Reaction Quotient How can we tell if a reaction has reached equilibrium?

2. What is the Reaction Quotient? K Q Equilibrium Constant Reaction Quotient Expression is ratio of products to reactants with balanced equation coefficients as powers Expression is ratio of products to reactants with balanced equation coefficients as powers Only includes gases and solutions Only includes gases and solutions To solve for K, plug in concentrations at equilibrium To solve for Q, plug in concentrations at any time

3. The Difference Between K and Q What exactly is the difference? 2 H2 (g) + O2 (g)  2 H2O (g) 2 H2 (g) + O2 (g)  2 H2O (g) The expressions for K and Q are the same. To solve for “K”, plug in concentrations at equilibrium only. To solve for “Q”, plug in concentrations right now.

4. Using Reaction Quotient [products now] [products at equilibrium] = K = Q [reactants now] [reactants at equilibrium] Q = K [now] = [equilibrium] System is at equilibrium Q > K [Products now] too large [Reactants now] too small System will make more reactants to reach equilibrium Q < K [Products now] too small [Reactants now] too large System will make more products to reach equilibrium

5. Let’s Practice For N2 (g) + O2 (g)  2 NO (g) if [N2] = 0.81 M, [O2] = 0.75 M and [NO] = 0.030 M, is the reaction at equilibrium if K = 0.0025? If not, which way will it go to reach equilibrium?

6. Let’s Practice For N2 (g) + O2 (g)  2 NO (g) if [N2] = 0.81 M, [O2] = 0.75 M and [NO] = 0.030 M, is the reaction at equilibrium if K = 0.0025? If not, which way will it go to reach equilibrium? Q = 0.0015 Q < K Reaction is not at equilibrium More products will need to be made (and also thereby reducing reactants) to have Q = K Reaction will go to the right to reach equilibrium