Figure: 15-01 Title: The equilibrium between N2O4(g) and NO2(g). Caption: (a) Frozen N2O4 is nearly colorless. (b) As N2O4 is warmed above its boiling point, it starts to dissociate into brown NO2 gas. (c) Eventually the color stops changing as N2O4(g) and NO2(g) reach equilibrium.

Figure: 15-02 Title: Achieving chemical equilibrium for N2O4(g) and NO2(g). Caption: (a) The concentration of N2O4 decreases while the concentration of NO2 increases during the course of the reaction. Equilibrium is indicated when the concentrations no longer change with time. (b) The rate of disappearance of N2O4 decreases with time as the concentration of N2O4 decreases. At the same time, the rate of formation of NO2 also decreases with time. Equilibrium occurs when the two rates are equal.

Figure: 15-03 Title: Partial pressure changes approaching equilibrium. Caption: (a) Equilibrium for the conversion of N2 and H2 to NH3 is approached beginning with H2 and N2 present in the ratio 3 : 1 and no NH3 present. (b) Equilibrium for the same reaction is approached beginning with only NH3 in the reaction vessel.

Figure: 15-04 Title: The Haber process. Caption: Used to convert N2(g) and H2(g) to NH3(g), this process, although exothermic, requires breaking the very strong triple bond in N2.

Figure: 15-06 Title: Concentration changes approaching equilibrium. Caption: As seen in Table 15.1, the same equilibrium mixture is produced starting with either 1.22 atm NO2 (Experiment 3) or 0.612 atm N2O4 (Experiment 4).

Figure: 15-07 Title: K and the composition of the equilibrium mixture. Caption: The equilibrium expression has products in the numerator and reactants in the denominator. (a) When K >> 1, there are more products than reactants at equilibrium, and the equilibrium is said to lie to the right. (b) When K << 1, there are more reactants than products at equilibrium, and the equilibrium is said to lie to the left.

Figure: 15-08 Title: A heterogeneous equilibrium. Caption: The equilibrium involving CaCO3, CaO, and CO2 is a heterogeneous equilibrium. The equilibrium pressure of CO2 is the same in the two bell jars as long as the two systems are at the same temperature, even though the relative amounts of CaCO3 and CaO differ greatly. The equilibrium-constant expression for the reaction is Kp = PCO2.

Figure: 15-09 Title: Predicting the direction of a reaction by comparing Q and K. Caption: The relative magnitudes of the reaction quotient Q and the equilibrium constant K indicate how the reaction mixture changes as it moves toward equilibrium. If Q is smaller than K, the reaction proceeds from left to right until Q = K. When Q = K, the reaction is at equilibrium and has no tendency to change. If Q is larger than K, the reaction proceeds from right to left until Q = K.

Figure: 15-10 Title: Effect of temperature and pressure on the percentage of NH3 in an equilibrium mixture of N2, H2, and NH3. Caption: Each mixture was produced by starting with a 3 : 1 molar mixture of H2 and N2. The yield of NH3 is greatest at the lowest temperature and at the highest pressure.

Figure: 15-11 Title: Effect of adding H2 to an equilibrium mixture of N2, H2, and NH3. Caption: When H2 is added to an equilibrium mixture of N2, H2, and NH3, a portion of the H2 reacts with N2 to form NH3, thereby establishing a new equilibrium position that has the same equilibrium constant. The results are shown in accordance with Le Châtelier’s principle.

Figure: 15-12 Title: Schematic diagram summarizing the industrial production of ammonia. Caption: Incoming N2 and H2 gases are heated to approximately 500ºC and passed over a catalyst. The resultant gas mixture is allowed to expand and cool, causing NH3 to liquefy. Unreacted N2 and H2 gases are recycled.

Figure: 15-13 Title: Effect of pressure on an equilibrium. Caption: Le Châtelier’s principle is illustrated for the effect of pressure changes on an equilibrium mixture of NO2 and N2O4.

Figure: 15-14 Title: Temperature and equilibrium. Caption: The reaction shown is Co(H2O)62+(aq) + 4 Cl−(aq) in equilibrium with CoCl42−(aq) + 6 H2O(l).

Figure: 15-15 Title: Effect of a catalyst on equilibrium. Caption: At equilibrium for the hypothetical reaction A in equilibrium with B, the forward reaction rate, rf, equals the reverse reaction rate, rr. The violet curve represents the path over the transition state in the absence of a catalyst. A catalyst lowers the energy of the transition state, as shown by the green curve. Thus, the activation energy is lowered for both the forward and the reverse reactions. As a result, the rates of forward and reverse reactions in the catalyzed reaction are increased.

Figure: 15-16 Title: Equilibrium and temperature. Caption: The graph shows how the equilibrium constant for the reaction ½ N2(g) + ½ O2(g) in equilibrium with NO(g) varies as a function of temperature. The equilibrium constant increases with increasing temperature because the reaction is endothermic. It is necessary to use a log scale for Kp because the values vary over such a large range.

Figure: 15 16-01UNE15-01 Title: Exercise 15.1 Caption: Energy profile.

Figure: 15 16-02UNE15-02 Title: Exercise 15.2 Caption: Spheres representing a hypothetical reaction.

Figure: 15 16-03UNE15-03 Title: Exercise 15.3 Caption: Equilibrium mixture.

Figure: 15 16-04UNE15-04 Title: Exercise 15.4 Caption: Reaction between red and blue spheres.

Figure: 15 16-05UNE15-05 Title: Exercise 15.5 Caption: Diagrams representing A2, B2, and AB molecules.

Figure: 15 16-06UNE15-06 Title: Exercise 15.6 Caption: Mixture of A atoms, A2 molecules, and AB molecules.

Figure: 15 16-07UNE15-07 Title: Exercise 15.7 Caption: Equilibrium state for the reaction between A2(g) and 2 B(g) in equilibrium with 2 AB(g).

Figure: 15 16-08UNE15-08 Title: Exercise 15.8 Caption: Equilibrium mixtures.

Figure: 15 16-09UNE15-80 Title: Exercise 15.80 Caption: Energy profile.

Figure: 15-T01 Title: Table 15.1 Caption: Initial and Equilibrium Concentrations of N2O4 and NO2 in the Gas Phase at 100ºC

Figure: 15-T02 Title: Table 15.2 Caption: Variation in Kp for N2 + 3 H2 in Equilibrium with 2 NH3 as a Function of Temperature