Chapter6

# 3 kj mol the hot pack contains 1400 g of water and

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Unformatted text preview: lution, ΔHsoln of CaCl2(s) is -81.3 kJ/ mol. The hot pack contains 140.0 g of water and 30.0 g of CaCl2(s). If the pack is initially at room temperature (21.0 °C), what temperature will the mixture become if the reaction goes to completion? Assume the speciﬁc heat capacity of the aqueous calcium chloride solution is 4.50 J K-1.g-1 and that the pack is held in a Reaction Vessel perfectly insulating container. Insulation Chem 6A Michael J. Sailor, UC San Diego Vent Stirrer Chem 6A Michael J. Sailor, UC San Diego Calorimetry: Solution 81.3 kJ mol mol CaCl2 30 g CaCl2 °C g 1000 J 110.98 g CaCl2 4.50 J 140+30 g solution kJ = 28.7 °C So ﬁnal temperature = 21 + 28.7 = +49.7 °C 6 Chem 6A Michael J. Sailor, UC San Diego Problem: Energy and reaction stoichiometry The thermochemical equation for the combustion of octane (gasoline) is shown below. If it takes 444 kJ of energy to get a 2000.0 pound car up to a speed of 70.0 mph, what volume of gasoline must be used to obtain this? Assume the engine is 100% efﬁcient and the density of octane is 0.70 g/mL. 2 C8H18(l) + 25 O2(g) → 16 CO2(g) + 18 H2O(l) (ΔH° = -10,942 kJ) 7 Chem 6A Michael J. Sailor, UC San Diego Solution: 444 kJ 2 mol C8H18 10,942 kJ 114.23 g C8H18 mol mL 0.7 g = 13.2 mL 8 Chem 6A Michael J. Sailor, UC San Diego Problem: Hess’ Law Given the standard enthalpy of formation of SO2(g) is -296.83 kJ/mol and the standard enthalpy of formation of SO3(g) is -395.72 kJ/ mol, what is the reaction enthalpy for the following reaction: 2SO2(g) + O2(g) → 2SO3(g) 9 Chem 6A Michael J. Sailor, UC San Diego Solution: ΔH (kJ/mol) S(s) + O2(g) → SO2(g) -296.83 S(s) + 3/2O2(g) → SO3(g) -395.72 Need: 2SO2(g) + O2(g) → 2SO3(g) ? 10 Chem 6A Michael J. Sailor, UC San Diego Solution: ΔH (kJ/mol) 2SO2(g) → 2S(s) + 2O2(g) 2(+296.83) 2S(s) + 3O2(g) → 2SO3(g) 2(-395.72) 2SO2(g) + O2(g) → 2SO3(g) -197.78 ΔH°reaction = -197.78 kJ/mol 11 Chem 6A Michael J. Sailor, UC San Diego Problem: The solid fuel in the booster stage of the space...
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## This note was uploaded on 11/16/2011 for the course CHEM 6A taught by Professor Pomeroy during the Spring '08 term at UCSD.

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