Chapter 13 Reaction Rates and Chemical Equilibrium Learning Goal Use the concept of reversible reactions to explain chemical equilibrium. © 2014 Pearson Education, Inc.

As the reactants SO2 and O2 collide, the forward reaction begins. Reversible Reactions As the reactants SO2 and O2 collide, the forward reaction begins. 2SO2(g) + O2(g) 2SO3 (g) SO3 molecules begin to form and collide with each other to form reactants in the reverse reaction. This reversible reaction is written with a double arrow. forward 2SO2(g) + O2(g) 2SO3(g) reverse © 2014 Pearson Education, Inc.

occurs in both the forward and reverse direction forward Reversible Reactions A reversible reaction occurs in both the forward and reverse direction forward 2SO2(g) + O2(g) 2SO3(g) reverse has two rates, a rate for the forward reaction and a rate for the reverse reaction © 2014 Pearson Education, Inc.

Write the forward and reverse reactions for the following: Learning Check Write the forward and reverse reactions for the following: CH4(g) + 2H2S(g) CS2(g) + 4H2(g) © 2014 Pearson Education, Inc.

Write the forward and reverse reactions for the following: Learning Check Write the forward and reverse reactions for the following: CH4(g) + 2H2S(g) CS2(g) + 4H2(g) The forward reaction is: The reverse reaction is: CS2(g) + 4H2(g) CH4(g) + 2H2S(g) © 2014 Pearson Education, Inc.

A reaction reaches chemical equilibrium when no further changes take place in the concentration of the reactants and products. At equilibrium, the rate of the forward reaction is equal to the rate of the reverse reaction the forward and reverse reactions continue at the same rate © 2014 Pearson Education, Inc.

Chemical Equilibrium As a reaction progresses, the rate of the forward reaction decreases and that of the reverse reaction increases until they become equal. © 2014 Pearson Education, Inc.

Chemical Equilibrium Equilibrium is reached when there is no further change in the concentrations of the reactants and products. © 2014 Pearson Education, Inc.

For the reaction at equilibrium H2(g) + I2(g) 2HI(g) the forward reaction is H2(g) + I2(g)  2HI(g) the reverse reaction is 2HI(g)  H2(g) + I2(g) the amounts of H2, I2, and HI are constant © 2014 Pearson Education, Inc.

Reaction Rates at Equilibrium © 2014 Pearson Education, Inc.

Complete each of the following with equal or not Learning Check Complete each of the following with equal or not equal, change or do not change. Before equilibrium is reached, the concentrations of the reactants and products_______. At equilibrium, the rate of the forward reaction is ______to the rate of the reverse reaction. © 2014 Pearson Education, Inc.

Complete each of the following with equal or not Solution Complete each of the following with equal or not equal, change or do not change. Before equilibrium is reached, the concentrations of the reactants and products change. At equilibrium, the rate of the forward reaction is equal to the rate of the reverse reaction. © 2014 Pearson Education, Inc.

Forward and Reverse Reactions Given the reaction: 2SO2(g) + O2(g) 2SO3(g) starting with the reactants, SO2 and O2, the product SO3 is formed until equilibrium is reached starting with only the product SO3, the reaction forms SO2 and O2 until equilibrium is reached © 2014 Pearson Education, Inc.

Forward and Reverse Reactions The equilibrium concentrations of SO2, O2, and SO3 are the same for both the forward and reverse reactions. © 2014 Pearson Education, Inc.

Complete each sentence with (1) equal (2) not equal (3) forward Learning Check Complete each sentence with (1) equal (2) not equal (3) forward (4) reverse (5) changes (6) does not change A. Reactants form products in the ________ reaction. B. At equilibrium, the reactant concentration _______. C. When products form reactants, it is the _______ reaction. © 2014 Pearson Education, Inc.

Complete each sentence with (1) equal (2) not equal (3) forward Solution Complete each sentence with (1) equal (2) not equal (3) forward (4) reverse (5) changes (6) does not change A. Reactants form products in the (3) forward reaction. B. At equilibrium, the reactant concentration (6) does not change. C. When products form reactants, it is the (4) reverse reaction. © 2014 Pearson Education, Inc.

Complete each sentence with (1) equal (2) not equal (3) forward Learning Check Complete each sentence with (1) equal (2) not equal (3) forward (4) reverse (5) changes (6) does not change At equilibrium, the rate of the forward reaction is ______ to the rate of the reverse reaction. B. If the forward reaction is faster than the reverse, the amount of products ______. © 2014 Pearson Education, Inc.

Complete each sentence with (1) equal (2) not equal (3) forward Learning Check Complete each sentence with (1) equal (2) not equal (3) forward (4) reverse (5) changes (6) does not change At equilibrium, the rate of the forward reaction is (1) equal to the rate of the reverse reaction. B. If the forward reaction is faster than the reverse, the amount of products (5) changes. © 2014 Pearson Education, Inc.