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101Q2_2006key

# 101Q2_2006key - 2 H 2(g O 2(g → 2H 2 O(l ΔH ° =...

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CHE 101 Summer Session I 2006 Quiz 2 Name ____________________________________________________ TA______________________________ You must show your work for partial credit. 1. (10 points) When 0.187 g of benzene, C 6 H 6 (molecular weight 78.06) is burned with oxygen in a bomb calorimeter which has a total heat capacity (calorimeter plus contents) of 1045 J/ ° C, the temperature of the calorimeter plus contents increases from 21.36 ° C to 28.84 ° C. What is the heat of combustion per mole of benzene? C 6 H 6 (l) + 9/2 O 2 (g) 6 CO 2 (g) + 3 H 2 O(g) ΔH = ? kJ/mol q reaction = -q calorimeter = (1045 J/ ° C)(28.84-21.36 ° C) = -7817 J = -7.82 kJ per mole: (actually ΔE = q) ΔH = (-7.82 kJ)/(0.187 gx1 mol/78.06 g) = -3.26x10 3 kJ/mol page 1 of 5

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CHE 101 Summer Session I 2006 Quiz 2 Name ________________________________ 2. (8 points) Calculate the standard enthalpy of formation of solid Mg(OH) 2 from the following data: 2 Mg(s) + O 2 (g) 2 MgO(s) ΔH ° = −1203.6 kJ/mol Mg(OH) 2 (s) MgO(s) + H 2 O(l) ΔH ° = +37.1 kJ/mol
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Unformatted text preview: 2 H 2 (g) + O 2 (g) → 2H 2 O(l) ΔH ° = −571.7 kJ/mol desired reaction is: Mg(s) + O 2 (g) + H 2 (g) → Mg(OH) 2 ΔH ° = ? kJ/mol ΔH ° = ½ (−1203.6 kJ/mol) + (−1)(37.1 kJ/mol) + ½ (−571.7 kJ/mol) = −924.8 kJ/mol page 2 of 5 CHE 101 Summer Session I 2006 Quiz 2 Name ________________________________ 3. (7 points) Octane, C 8 H 18 (l) (molecular weight 114.3) reacts with oxygen, O 2 (g) (molecular weight 32.0)to form CO 2 (g) (molecular weight 44.01)and H 2 O(l) (molecular weight 18.02). Using the data below calculate the heat of combustion for 1.0 g of octane at 298 K. ΔH f ° (kJ/mol) C 8 H 18 (l)-250.1 O 2 (g) CO 2 (g)-393.5 H 2 O(l)-285.83 C 8 H 18 (l) + 25/2 O 2 (g) → 8 CO 2 (g) + 9 H 2 O(g) ΔH = ? kJ/mol ΔH ° = {9 x −285.83 kJ/mol) + (8 x −393.5 kJ/mol)} − (−250.1 kJ/mol) = −5.470x10 3 kJ/mol (−5.470x10 3 kJ/mol)(1.0 g/114.3 g/mol) = −48 kJ page 3 of 5...
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