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Chapter 15: Chemical Equilibrium

Invite you to consult the lecture content "Chapter 15: Chemical Equilibrium" below. Contents of lectures introduce to you the content: The concept of equilibrium, the equilibrium constant, le châtelier’s principle. Hopefully document content to meet the needs of learning, work effectively. | Copyright 1999, PRENTICE HALL Chapter 15 Chemical Equilibrium Chapter 15 David P. White University of North Carolina, Wilmington 1 1 1 1 Copyright 1999, PRENTICE HALL Chapter 15 The Concept of Equilibrium Consider colorless frozen N2O4. At room temperature, it decomposes to brown NO2: N2O4(g) 2NO2(g). At some time, the color stops changing and we have a mixture of N2O4 and NO2. Chemical equilibrium is the point at which the concentrations of all species are constant. Using the collision model: as the amount of NO2 builds up, there is a chance that two NO2 molecules will collide to form NO2. At the beginning of the reaction, there is no NO2 so the reverse reaction (2NO2(g) N2O4(g)) does not occur. Copyright 1999, PRENTICE HALL Chapter 15 The Concept of Equilibrium Copyright 1999, PRENTICE HALL Chapter 15 The Concept of Equilibrium The point at which the rate of decomposition: N2O4(g) 2NO2(g) equals the rate of dimerization: 2NO2(g) N2O4(g). is dynamic . | Copyright 1999, PRENTICE HALL Chapter 15 Chemical Equilibrium Chapter 15 David P. White University of North Carolina, Wilmington 1 1 1 1 Copyright 1999, PRENTICE HALL Chapter 15 The Concept of Equilibrium Consider colorless frozen N2O4. At room temperature, it decomposes to brown NO2: N2O4(g) 2NO2(g). At some time, the color stops changing and we have a mixture of N2O4 and NO2. Chemical equilibrium is the point at which the concentrations of all species are constant. Using the collision model: as the amount of NO2 builds up, there is a chance that two NO2 molecules will collide to form NO2. At the beginning of the reaction, there is no NO2 so the reverse reaction (2NO2(g) N2O4(g)) does not occur. Copyright 1999, PRENTICE HALL Chapter 15 The Concept of Equilibrium Copyright 1999, PRENTICE HALL Chapter 15 The Concept of Equilibrium The point at which the rate of decomposition: N2O4(g) 2NO2(g) equals the rate of dimerization: 2NO2(g) N2O4(g). is dynamic equilibrium. The equilibrium is dynamic because the reaction has not stopped: the opposing rates are equal. Consider frozen N2O4: only white solid is present. On the microscopic level, only N2O4 molecules are present. Copyright 1999, PRENTICE HALL Chapter 15 The Concept of Equilibrium Copyright 1999, PRENTICE HALL Chapter 15 The Concept of Equilibrium As the substance warms it begins to decompose: N2O4(g) 2NO2(g) A mixture of N2O4 (initially present) and NO2 (initially formed) appears light brown. When enough NO2 is formed, it can react to form N2O4: 2NO2(g) N2O4(g). At equilibrium, as much N2O4 reacts to form NO2 as NO2 reacts to re-form N2O4: The double arrow implies the process is dynamic. Copyright 1999, PRENTICE HALL Chapter 15 The Concept of Equilibrium Consider Forward reaction: A B Rate = kf[A] Reverse reaction: B A Rate = kr[B] At equilibrium kf[A] = kr[B]. Therefore, For an equilibrium we write As the reaction progresses [A] decreases to a constant, [B] .