# 7.E: Energy and Chemical Processes (Exercises)

1. Sulfur dioxide (SO2) is a pollutant gas that is one cause of acid rain. It is oxidized in the atmosphere to sulfur trioxide (SO3), which then combines with water to make sulfuric acid (H2SO4).

1. Write the balanced reaction for the oxidation of SO2 to make SO3. (The other reactant is diatomic oxygen.)
2. When 1 mol of SO2 reacts to make SO3, 23.6 kcal of energy are given off. If 100 lb (1 lb = 454 g) of SO2 were converted to SO3, what would be the total energy change?
2. Ammonia (NH3) is made by the direct combination of H2 and N2 gases according to this reaction:

N2(g) + 3H2(g) → 2NH3(g) + 22.0 kcal

1. Is this reaction endothermic or exothermic?
2. What is the overall energy change if 1,500 g of N2 are reacted to make ammonia?
3. A 5.69 g sample of iron metal was heated in boiling water to 99.8°C. Then it was dropped into a beaker containing 100.0 g of H2O at 22.6°C. Assuming that the water gained all the heat lost by the iron, what is the final temperature of the H2O and Fe?

4. A 5.69 g sample of copper metal was heated in boiling water to 99.8°C. Then it was dropped into a beaker containing 100.0 g of H2O at 22.6°C. Assuming that the water gained all the heat lost by the copper, what is the final temperature of the H2O and Cu?

5. When 1 g of steam condenses, 540 cal of energy is released. How many grams of ice can be melted with 540 cal?

6. When 1 g of water freezes, 79.9 cal of energy is released. How many grams of water can be boiled with 79.9 cal?

7. The change in energy is +65.3 kJ for each mole of calcium hydroxide [Ca(OH)2] according to the following reaction:

Ca(OH)2(s) → CaO(s) + H2O(g)

How many grams of Ca(OH)2 could be reacted if 575 kJ of energy were available?

8. The thermite reaction gives off so much energy that the elemental iron formed as a product is typically produced in the liquid state:

2Al(s) + Fe2O3(s) → Al2O3(s) + 2Fe(ℓ) + 204 kcal

How much heat will be given off if 250 g of Fe are to be produced?

9. A normal adult male requires 2,500 kcal per day to maintain his metabolism.

1. Nutritionists recommend that no more than 30% of the calories in a person’s diet come from fat. At 9 kcal/g, what is the maximum mass of fat an adult male should consume daily?
2. At 4 kcal/g each, how many grams of protein and carbohydrates should an adult male consume daily?
10. A normal adult male requires 2,500 kcal per day to maintain his metabolism.

1. At 9 kcal/g, what mass of fat would provide that many kilocalories if the diet was composed of nothing but fats?
2. At 4 kcal/g each, what mass of protein and/or carbohydrates is needed to provide that many kilocalories?
11. The volume of the world’s oceans is approximately 1.34 × 1024 cm3.

1. How much energy would be needed to increase the temperature of the world’s oceans by 1°C? Assume that the heat capacity of the oceans is the same as pure water.
2. If Earth receives 6.0 × 1022 J of energy per day from the sun, how many days would it take to warm the oceans by 1°C, assuming all the energy went into warming the water?
12. Does a substance that has a small specific heat require a small or large amount of energy to change temperature? Explain.

13. Some biology textbooks represent the conversion of adenosine triphosphate (ATP) to adenosine diphosphate (ADP) and phosphate ions as follows:

ATP → ADP + phosphate + energy

What is wrong with this reaction?

14. Assuming that energy changes are additive, how much energy is required to change 15.0 g of ice at −15°C to 15.0 g of steam at 115°C? (Hint: you will have five processes to consider.)

1. 2SO2 + O2 → 2SO3
2. 16,700 kcal
2.
1. exothermic
2. 1177 kcal

5. 6.76 g

6. 0.148 g

1. 652 g

8. 457 kcal
1. 83.3 g
2. 438 g
10.
a. 278 g
b. 625 g

11.

1. 1.34 × 1024 cal
2. 93 days

12. A substance with smaller specific heat requires less energy per unit of mass to raise its temperature,

13. A reactant is missing: H2O is missing.

14. Total energy = 11,019 cal