Ch.7 Chemical Reactions: Energy, Rate and Equilibrium
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Problem 1
The change of state from liquid H2O to gaseous H2O has ∆H = +9.72 kcal/mol(+40.7 kJ/mol) and ∆S = -26.1 cal/(mol • K) [-109 J/(mol •K)]. What are the values of ∆H and ∆S (in kcal/mol and kJ/mol) for the change from gaseous to liquid H2O?Problem 1
The change of state from liquid H2O to gaseous H2O has ∆H = +9.72 kcal/mol(+40.7 kJ/mol) and ∆S = -26.1 cal/(mol • K) [-109 J/(mol •K)]. Is the change from liquid to gaseous H2O favored or unfavored by ∆H? By ∆S?Problem 3
In photosynthesis, green plants convert carbon dioxide and water into glucose (C6H12O6) according to the following equation: 6 CO2(g) + 6 H2O(l) → C6H12O6(aq) + 6 O2(g) Estimate ∆H for the reaction using bond dissociation energies from Table 7.1. Give your answer in kcal/mol and kJ/mol. (C6H12O6 has five C―C bonds, seven C―H bonds, seven C―O bonds, and five O―H bonds).Problem 3
In photosynthesis, green plants convert carbon dioxide and water into glucose (C6H12O6) according to the following equation: 6 CO2(g) + 6 H2O(l) → C6H12O6(aq) + 6 O2(g) Is the reaction endothermic or exothermic?Problem 4
The following equation shows the conversion of aluminum oxide (from the ore bauxite) to aluminum: 2 Al2O3(s) → 4 Al(s) + 3 O2(g) ∆H = +801 kcal/mol (+3350 kJ/mol) How many kilocalories are required to produce 10.0 g of aluminum? How many kilojoules?Problem 7
Does entropy increase or decrease in the following processes? Polymeric complex carbohydrates are metabolized by the body, converted into smaller simple sugars.Problem 7
Does entropy increase or decrease in the following processes? 2 SO2(g) + O2(g) → 2 SO3(g)Problem 12
Do the following reactions favor reactants or products at equilibrium? Give relative concentrations at equilibrium. Sucrose(aq) + H2O(l) ⇌ Glucose(aq) + Fructose(aq) K = 1.4 x 10^5Problem 12
Do the following reactions favor reactants or products at equilibrium? Give relative concentrations at equilibrium. Fe2O3(s) + 3 CO(g) ⇌ 2 Fe(s) + 3 CO2(g) K (at 727 °C) = 24.2Problem 14
The following diagrams represent two similar reactions that have achieved equilibrium: <.> Write the expression for the equilibrium constant for each reaction.Problem 14
The following diagrams represent two similar reactions that have achieved equilibrium: <
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Calculate the value for the equilibrium constant for each reaction.Problem 15
Is the yield of SO3 at equilibrium favored by a higher or lower pressure? By a higher or lower temperature? 2 SO2(g) + O2 ⇌ 2 SO3(g) ∆H = -47 kcal/molProblem 16
What effect do the listed changes have on the position of the equilibrium in the reaction of carbon with hydrogen? C(s) + 2 H2(g) ⇌ CH4(g) ∆H = -18 kcal/mol (-75kJ/mol) Allowing CH4 to escape continuously from the reaction vesselProblem 16
What effect do the listed changes have on the position of the equilibrium in the reaction of carbon with hydrogen? C(s) + 2 H2(g) ⇌ CH4(g) ∆H = -18 kcal/mol (-75kJ/mol) Increasing pressure by decreasing volumeProblem 16
What effect do the listed changes have on the position of the equilibrium in the reaction of carbon with hydrogen? C(s) + 2 H2(g) ⇌ CH4(g) ∆H = -18 kcal/mol (-75kJ/mol) Increasing temperatureProblem 21
Two curves are shown in the following energy diagram:Which curve represents the spontaneous reaction, and which the nonspontaneous? 
Problem 21.27
What energy requirements must be met in order for a reaction to be favorable?
Problem 22
The following diagram portrays a reaction of the type A(s) → B(g) + C(g), where the different-colored spheres represent different molecular structures. Assume that the reaction has ∆H = +9.1 kcal/mol (+38.1 kJ/mol).
What is the sign of ∆S for the reaction?
Problem 22
The following diagram portrays a reaction of the type A(s) → B(g) + C(g), where the different-colored spheres represent different molecular structures. Assume that the reaction has ∆H = +9.1 kcal/mol (+38.1 kJ/mol).
Is the reaction likely to be spontaneous at all temperatures, nonspontaneous at all temperatures, or spontaneous at some but nonspontaneous at others?
Problem 23
Is the total enthalpy (H) of the reactants for an endothermic reaction greater than or less than the total enthalpy of the products?Problem 25
The vaporization of Br2 from the liquid to the gas state requires 7.4 kcal/mol (31.0 kJ/mol). What is the sign of ∆H for this process? Write a reaction showing heat as a product or reactant.Problem 25
The vaporization of Br2 from the liquid to the gas state requires 7.4 kcal/mol (31.0 kJ/mol). How many kilojoules are needed to evaporate 82 g of Br2?Problem 26
Converting liquid water to solid ice releases 1.44 kcal/mol (6.02 kJ/mol). How many kilocalories are released by freezing 32 g of H2O?Problem 27
Acetylene (H―C= C―H) is the fuel used in welding torches. Estimate ∆H for this reaction (in kJ/mol) using the bond energies listed in Table 7.1.Problem 28
Nitrogen in air reacts at high temperatures to form NO2 according to the following reaction: N2 + 2 O2 → 2 NO2 Estimate ∆H for this reaction (in kcal and kJ) using the bond energies from Table 7.1.Problem 29
Glucose, also known as 'blood sugar' when measured in blood, has the formula C6H12O6. What is the minimum amount of energy (in kJ) a plant must absorb to produce 15.0 g of glucose?Problem 31
Which of the following processes results in an increase in entropy of the system? a. A drop of ink spreading out when it is placed in water b. Steam condensing into drops on windows c. Constructing a building from loose bricksProblem 32
For each of the following processes, specify whether entropy increases or decreases. Explain each of your answers. Assembling a jigsaw puzzleProblem 33
What two factors affect the spontaneity of a reaction?Problem 34
What is the difference between an exothermic reaction and an exergonic reaction?
