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5 Thermochemistry Solutions to Exercises (c) %H = 56.108 = 14.37% H (a) + = 4(-393.5 kJ) + 5(-285.83 - 13/2(0) = (b) 1 -2878.5kJ mol C₄H₁₀ X 1 mol C₄H₁₀ = 49.523 50kJ/g (c) (d) It is certainly true that as the mass % H increases, the fuel value (kJ/g) of the hydrocarbon increases, given the same number of C atoms. A graph of the data in parts (b) and (c) (see below) suggests that mass % H and fuel value are directly proportional when the number of C atoms is constant. 50 49 Fuel Value 48 47 46 10 11 12 13 14 15 16 17 18 %H 5.109 = d. Be careful with units. 200 lb 2.205 1kg lb X 9.81 s² m time 45 ft 1 3ft yd X 1.0936 m yd 20 times = 1 Cal = 1 kcal = kJ 4.1841 1Cal = 58.34 = 58 Cal No, if all work is used to increase the man's potential energy, 20 rounds of stair- climbing will not compensate for one extra order of 245 Cal fries. In fact, more than 58 Cal of work will be required to climb the stairs, because some energy is required to move limbs and some energy will be lost as heat (see Solution 5.96). 5.110 Plan. Use dimensional analysis to calculate the amount of solar energy supplied per m² in 1 hr. Use stoichiometry to calculate the amount of plant energy used to produce sucrose per in 1 hr. Calculate the ratio of energy for sucrose to total solar energy, per m² per hr. 134