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Chapter 16
Principles of Chemical Equilibrium

 
   
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The temperature dependent equilibrium of NO2 with N2O4 is demonstrated.
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NO2--N2O4 equilibrium. The red-brown gas NO2 exists in equilibrium with colorless N2O4. When a tube containing the equilibrium mixture is put into hot water, the equilibrium is shifted in the direction of NO2 so more of the reddish-brown gas is present. As the temperature is decreased the equilibrium shifts in favor of colorless N2O4. The color fades when the tube is placed in an ice bath and NO2 is converted to N2O4.
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A solution of CuSO4 is prepared starting with solid CuSO4.
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A calculated amount of solid CuSO4 is weighed out and added to a volumetric flask. Some water is added and the flask is shaken to dissolve the solid. Once the CuSO4 has dissolved, enough water is added to make the volume exactly 250. mL. It should be pointed out that the volume of the solution may change as the CuSO4 dissolves so it must be completely dissolved before filling the volumetric flask to the mark.
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Dissolution of NaCl in aqueous solution.
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When an ionic substance dissolves in water the ions are solvated by water molecules. The hydrogen atoms of the water molecule, which have a partial positive charge, interact with the chloride ion. The oxygen atom of the water molecule, which has a partial negative charge, interacts with the sodium ion. Each ion is surrounded by several water molecules.
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Le Chatelier's Principle
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Temperature dependent equilibrium between NO2 and N2O4
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In a closed container the reddish-brown gas NO2 is in equilibrium with the colorless gas N2O4. According to Le Chatelier's principle when the temperature of an equilibrium system is increased at constant volume the equilibrium shifts in the direction that absorbs heat. Since the conversion of 2NO2 to N2O4 is an exothermic reaction, the equilibrium shifts in favor of NO2 when the temperature is increased from 373 K to 473 K.
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Removal of water from sugar by H2SO4
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The formula of table sugar is C12H22O11. Sugars were originally named carbohydrates (hydrates of carbon) because they have a ratio of H to O of 2:1. When H2SO4 is added to sugar, the sugar is converted to H2O and solid C. The reaction is exothermic so the water is converted to steam. A column of solid C rises out of the beaker during the reaction.
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The temperature dependent equilibrium of NO2 with N2O4 is demonstrated.
Notes
NO2--N2O4 equilibrium. The red-brown gas NO2 exists in equilibrium with colorless N2O4. When a tube containing the equilibrium mixture is put into hot water, the equilibrium is shifted in the direction of NO2 so more of the reddish-brown gas is present. As the temperature is decreased the equilibrium shifts in favor of colorless N2O4. The color fades when the tube is placed in an ice bath and NO2 is converted to N2O4.
16.1
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16-2
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Dynamic equilibrium in a physical process.
16.3
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Three approaches to equilibrium in the reaction CO(g) 1 2 H2(g) zy CH3OH(g). The initial and equilibrium amounts for each of these three cases are listed in Table 16.1. te 5 time for equilibrium to be reached.
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16.4
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Equilibrium in thre reaction….
16.5
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Predicting the direction of net change in a reversible reaction. Five possibilities for the relationship of initial and equilibrium conditions are shown. From Table 16.1 and Figure 16-2, Experiment 1 corresponds to initial condition (a); Experiment 2 to condition (e); and Experiment 3 to (d). The situation in Example 16-5 also corresponds to condition (d).
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16.6
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Changing equilibrium conditions by changing the amount of a reactant 2 SO2(g) 1 O2(g) zy 2 SO3(g), Kc 5 2.8 3 102 at 1000 K. (a) The original equilibrium condition. (b) Disturbance caused by adding 1.00 mol SO3. (c) The new equilibrium condition (as calculated in Exercise 72). The amount of SO3 in the new equilibrium mixture (c), 1.46 mol, is greater than the original 0.68 mol (a), but it is not as great as immediately after the addition of 1.00 mol SO3 in (b), 1.68 mol. The effect of adding SO3 to an equilibrium mixture is partially offset when equilibrium is restored.
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16.7
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16-7
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Effect of pressure change on equilibrium in the reaction 2 SO2(g) 1 O2(g) zy 2 SO3(g). An increase in external pressure causes a decrease in the reaction volume and a shift in equilibrium “to the right.” (See Exercise 72 for a calculation of the new equilibrium amounts.)
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16.8
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The equilibrium N2O4(g)…
16.9
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Determining Kc or Kp from experimental data
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16.10
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Equilibrium in the reaction N2O4(g) zy 2 NO2(g) at 25 °C-Example 16-12 illustrated. Each “molecule” illustrated represents 0.001 mol. (a) Initially, the bulb contains 0.024 mol N2O4, represented by 24 “molecules.” (b) At equilibrium, some molecules of N2O4 have dissociated to NO2. The 21 “molecules” of N2O4 and 6 of NO2 correspond to 0.021 mol N2O4 and 0.006 mol NO2 at equilibrium
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16.11
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16-11
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Determining equilibrium concentrations or partial pressures
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16.13
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16-13
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Equilibrium conversion of N2(g) and H2(g)….
P 628-3a
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Dissolution of NaCl in water
p 641-3
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p 641-3
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Le Chatelier's principle
p 803-3
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p 803-3
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Temperature dependence of equilibrium
p 922-3a
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p 922-3a
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Dehydration of sugar
p 627-1a
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Methanol as althernative to gasoline
P 630-1a
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Equilibrium concentration data from table 16.1
P 642-1
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2 SO2(g)+….
P 646
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P 646
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Sulfuric acid is produced from SO3
P 647-1
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P 647-1
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The Lewis structures of N2)4….
P 656-1a
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P 656-1a
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Use of liquid ammonia as a fertilizer…
P 657-1a
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P 657-1a
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During electrical storms, N2(g)….
P 660-1a
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Diagram of two unequally sized bulbs joined
P 660-1
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P 660-1
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Digram in 4 parts of mixtures
P 661-1
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P 661-1
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Sketch of mixtures in 4 parts.
Table 16.1
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Table 16.1
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Three approaches to equilibrium in the reaction….
Table 16.3
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Table 16.3
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Equilibrium constants of some common reactions