# End of Chapter Material

Additional Exercises

- Use bond energies to estimate the energy change of this reaction.
C

_{3}H_{8}+ 5 O_{2}→ 3 CO_{2}+ 4 H_{2}ONote: C

_{3}H_{8}is made up of two C-C bonds and 8 C-H bonds.**Bond Energies**C−H = 413 kJ/mol

C−C = 348 kJ/mol

O=O = 495 kJ/mol

O-H = 463 kJ/mol

- Use bond energies to estimate the energy change of this reaction.
N

_{2}H_{4}+ O_{2}→ N_{2}+ 2H_{2}**Bond Energies**N-H = 391 kJ/mol

O=O = 495 kJ/mol

N=N = 945 kJ/mol

O-H = 463 kJ/mol

- Is the following reaction endothermic or exothermic?
PCl

_{3 }(g) + Cl_{2 }(g) ⇄ PCl_{5 }(g) + 60 kJ - Is the following reaction endothermic or exothermic?
N

_{2}O_{4 }(g) + 57 kJ ⇄ 2NO_{2 }(g) - Determine how much energy is given off when 67.9 g of H
_{2}reacts in the following thermochemical equation: - Determine how much energy is given off when 75.3 g of NH
_{3}is produced in the following thermochemical equation: - Does entropy increase or decrease for the following reaction?
PCl

_{3 }(g) + Cl_{2 }(g) ⇄ PCl_{5}(g) + 60 kJ - Does entropy increase or decrease for the following reaction?
N

_{2}O_{4 }(g) + 57 kJ ⇄ 2NO_{2 }(g) - Does a very large
*K*_{eq}favor the reactants or the products? Explain your answer. - Is the
*K*_{eq}for reactions that favor reactants large or small? Explain your answer. - Write the equilibrium expression for: 2 HF (g) ⇄ H
_{2}(g) + F_{2}(g) - Write the equilibrium expression for: 4 NH
_{3 }(g) +7 O_{2 }(g) ⇌ 4 NO_{2 }(g) + 6 H_{2}O (g) - Write the equilibrium expression for: 2 PbO (s) + O
_{2}(g) ⇄ 2 PbO_{2 }(s) - How will the equation shift if more HF (g) is added? 2 HF (g) ⇄ H
_{2}(g) + F_{2}(g) - How will the equation shift if more F
_{2}(g) is added? 2 HF (g) ⇄ H_{2}(g) + F_{2}(g) - How will the equation shift if the pressure is increased? 2 HF (g) ⇄ H
_{2}(g) + F_{2}(g) - How will the equation shift if the pressure is reduced? 2 HF (g) ⇄ H
_{2}(g) + F_{2}(g) - How will the equation shift if the temperature is increased? N
_{2}O_{4 }(g) + 57 kJ ⇄ 2NO_{2 }(g) - How will the equation shift if the temperature is decreased? N
_{2}O_{4 }(g) + 57 kJ ⇄ 2NO_{2 }(g)

Answers

1. −2,023 kJ

3. Exothermic

5. -1030 kJ

7.. Entropy decreases as 2 moles of gas go to 1 mole of gas

9. Favors products because the numerator of the ratio for the Keq is larger than the denominator

11. [latex]K_{\text{eq}}=\dfrac{[\ce{H2}][\ce{F2}]}{[\ce{HF}]^2}[/latex]

13.[latex]K_{\text{eq}}=\dfrac{\ce{1}}{[\ce{O2}]}[/latex]

15. The reaction will shift to the left

17. There will be no impact on the reaction since there are 2 moles of gas on both sides of the equation

19. The reaction will shift to the left