1 (122)

Prévia do material em texto

120 Chapter 6 Thermochemistry 6.91 Given: + + + and = -1418.4 kJ Find: Conceptual Plan: Fill known values into = - and rearrange to solve for Solution: Reactant/Product (kJ/mol from Appendix IIB) 0.0 -393.5 -285.8 N₂(g) 0.0 Be sure to pull data for the correct formula and phase. = - = - (-1418.4kJ) = [2(-393.5kJ) + 3(-285.8kJ) + 1(0.0kJ) + 1418.4kJ = [-1644.4kJ] = -113.0kJ/mol Check: The units (kJ/mol) are correct. The answer is negative (but not as negative as water and carbon dioxide), which is consistent with an exothermic combustion reaction. Energy Use and the Environment 6.93 (a) Given: methane, = -802.3 kJ; = 1.00 X 10² kJ Find: m(CO₂) Conceptual Plan: q mol g 1 mol 44.01 g 1 mol Solution: 44.01 = 5.49 CO₂ Check: The units (g) are correct. The magnitude of the answer (~5) makes physical sense because less than a mole of fuel is used. (b) Given: propane, = -2043 kJ; = 1.00 X 10² kJ Find: m(CO₂) Conceptual Plan: q mol g CO2 3 mol 44.01 -2043 kJ 1 mol Solution: -2043 X = 6.46 CO₂ Check: The units (g) are correct. The magnitude of the answer (~6) makes physical sense because less than a mole of fuel is used. (c) Given: octane, = -5074.1 kJ; q = 1.00 X 10² kJ Find: m(CO₂) Conceptual Plan: q mol CO₂ g 8 mol 44.01 -5074.1kJ 1 mol Solution: Check: The units (g) are correct. The magnitude of the answer (~7) makes physical sense because less than a mole of fuel is used. The methane generated the least carbon dioxide for the given amount of heat, while the octane generated the most carbon dioxide for the given amount of heat. Copyright © 2017 Pearson Education, Inc.