Ch.7 Chemical Reactions: Energy, Rate and Equilibrium
Back
- 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 1
- 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 3
- 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 4
- 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 7
- 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 10^5
Problem 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) = 24.2
Problem 12
- 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: <
Problem 14
.>
Calculate the value for the equilibrium constant for each reaction. - 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/mol
Problem 15
- 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 vessel
Problem 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 volume
Problem 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 temperature
Problem 16
- Two curves are shown in the following energy diagram:
Problem 21
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?
- 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).
Problem 22
What is the sign of ∆S for the reaction?
- 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).
Problem 22
Is the reaction likely to be spontaneous at all temperatures, nonspontaneous at all temperatures, or spontaneous at some but nonspontaneous at others?
- Is the total enthalpy (H) of the reactants for an endothermic reaction greater than or less than the total enthalpy of the products?
Problem 23
- 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 25
- 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 26
- 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 27
- 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 28
- 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 29
- 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 bricks
Problem 31
- For each of the following processes, specify whether entropy increases or decreases. Explain each of your answers. Assembling a jigsaw puzzle
Problem 32
- What two factors affect the spontaneity of a reaction?
Problem 33
- What is the difference between an exothermic reaction and an exergonic reaction?
Problem 34
