Chapter 13 Reaction Rates and Chemical Equilibrium 13.4 Using Equilibrium Constants Learning Goal Use an equilibrium constant to predict the extent of the reaction and to calculate equilibrium concentrations. © 2014 Pearson Education, Inc.

Using Equilibrium Constants The values of Kc can be large or small, depending on whether equilibrium is reached with more products than reactants equilibrium is reached with more reactants than products However, the size of the equilibrium constant does not affect how fast equilibrium is reached. © 2014 Pearson Education, Inc.

Equilibrium with a Large Kc Reactions with a large Kc have large amounts of products produced from the forward reaction at equilibrium. The equilibrium constant for the reaction of SO2 and O2 has a large Kc. 2SO2(g) + O2(g) 2SO3(g) © 2014 Pearson Education, Inc.

Equilibrium with a Large Kc At equilibrium, the reaction mixture contains mostly products and a small amount of reactants. 2SO2(g) + O2(g) 2SO3(g) © 2014 Pearson Education, Inc.

Equilibrium with a Large Kc Insert figure 13.8 with caption pg 451. In the reaction of SO2(g) and O2(g), the equilibrium mixture contains mostly product SO3(g), which results in a large Kc. © 2014 Pearson Education, Inc.

Equilibrium with a Small Kc Reactions with a small Kc have an equilibrium mixture with a low concentration of products and a high concentration of reactants. The equilibrium constant for the reaction of N2 and O2 has a small Kc. N2(g) + O2(g) 2NO(g) © 2014 Pearson Education, Inc.

Equilibrium with a Small Kc At equilibrium, the reaction mixture contains a small amount of products and a large amount of reactants. N2(g) + O2(g) 2NO(g) © 2014 Pearson Education, Inc.

Equilibrium with a Small Kc The equilibrium mixture contains a very small amount of the product NO and a large amount of the reactants N2 and O2, which results in a small Kc. © 2014 Pearson Education, Inc.

Equilibrium Constants, Kc Reactions with equilibrium constants close to 1 have equal concentrations of reactants and products at equilibrium. At equilibrium, a reaction with a large Kc contains mostly products, whereas a reaction with a small Kc contains mostly reactants. © 2014 Pearson Education, Inc.

Equilibrium Constants, Kc © 2014 Pearson Education, Inc.

Learning Check For each Kc, indicate whether the reaction mixture at equilibrium contains mostly reactants or products. © 2014 Pearson Education, Inc.

For each Kc, indicate whether the reaction mixture Solution For each Kc, indicate whether the reaction mixture at equilibrium contains mostly reactants or products. Kc is large; products are favored at equilibrium. Kc is small; reactants are favored at equilibrium. © 2014 Pearson Education, Inc.

Calculating Concentrations at Equilibrium © 2014 Pearson Education, Inc.

At equilibrium, the reaction Learning Check At equilibrium, the reaction has the concentrations: [PCl3] = [Cl2] = 0.10 M. What is the concentration of PCl5 at equilibrium? © 2014 Pearson Education, Inc.

At equilibrium, the reaction Solution At equilibrium, the reaction What is the concentration of PCl5 at equilibrium? Step 1 State the given and needed quantities. Given Need © 2014 Pearson Education, Inc.

At equilibrium, the reaction Solution At equilibrium, the reaction What is the concentration of PCl5 at equilibrium? Step 2 Write the Kc expression for the equilibrium and solve for the needed concentration. © 2014 Pearson Education, Inc.

At equilibrium, the reaction Solution At equilibrium, the reaction What is the concentration of PCl5 at equilibrium? Step 3 Substitute the equilibrium molar concentrations and calculate the needed concentration. © 2014 Pearson Education, Inc.