Chapter5WorksheetKEY

[7] When 50.0 mL of 0.100 M AgNO 3 and 50.0 mL of 0.100 M HCl are mixed in a constant-pressure calorimeter, the temperature of the mixture increases from 22.20°C to 23.11°C. The temperature increase is caused by the following reaction AgNO 3 (aq) + HCl(aq) → AgCl(s) + HNO 3 (aq) Calculate ∆ H for this reaction in kJ/mol assuming that the combined solution has a mass of 100.0 g and a specific heat of 4.18 J/g°C 𝑞𝑞 𝑐𝑐𝑤𝑤𝑐𝑐𝑐𝑐𝑤𝑤𝑐𝑐𝑐𝑐𝐹𝐹𝑤𝑤𝐹𝐹𝑤𝑤 = 100.0 𝑔𝑔 × 4.18 𝐽𝐽 𝑔𝑔℃ × {23. 11℃ − 22. 20℃ } = 380.38 𝐽𝐽 ; 𝑞𝑞 𝑤𝑤𝑟𝑟𝑟𝑟 = − 380.38 𝐽𝐽 = − 0.38038 𝑘𝑘𝐽𝐽 𝑚𝑚𝑚𝑚𝑚𝑚 = 0.1 𝑚𝑚𝑚𝑚𝑚𝑚 𝐿𝐿 × 0.05 𝑚𝑚 = 0.005 𝑚𝑚𝑚𝑚𝑚𝑚 ; ∆𝐻𝐻 𝑤𝑤𝑟𝑟𝑟𝑟 = −0 . 38038 𝑘𝑘𝐽𝐽 0 . 005 𝑐𝑐𝑐𝑐𝑐𝑐 = − 76.08 𝑘𝑘𝐽𝐽 / 𝑚𝑚𝑚𝑚𝑚𝑚 [8] Methyl hydrazine (CH 6 N 2 ) is commonly used as a liquid rocket fuel. The combustion of methyl hydrazine with oxygen produces N 2 (g), CO 2 (g), and H 2 O(l): 2CH 6 N 2 (l) + 5O 2 (g) → 2CO 2 (g) + 6H 2 O(l) + 4N 2 (g) When 4.00 g of methyl hydrazine is combusted in a bomb calorimeter, the temperature of the calorimeter increases from 25.00°C to 39.50°C. In a separate experiment the heat capacity of the calorimeter is measured to be 7.794 kJ/°C. What is the heat of reaction for the combustion of a mole of CH 6 N 2 in this calorimeter? {FW = 46.07} 𝑞𝑞 𝑐𝑐𝑤𝑤𝑐𝑐𝑐𝑐𝑤𝑤 . = 7.794 𝑘𝑘𝑘𝑘 ℃ × {39. 50℃ − 25. 00℃ } = 113.013 𝑘𝑘𝐽𝐽 ; 𝑚𝑚𝑚𝑚𝑚𝑚 = 4.00 𝑔𝑔 × 1 𝑐𝑐𝑐𝑐𝑐𝑐 46 . 07 𝑔𝑔 = 0.0868 𝑚𝑚𝑚𝑚𝑚𝑚 𝑞𝑞 𝑤𝑤𝑟𝑟 = − 113.013 𝑘𝑘𝐽𝐽 ; ∆𝐻𝐻 𝑤𝑤𝑟𝑟𝑟𝑟 = −113 . 013 𝑘𝑘𝐽𝐽 0 . 0868 𝑐𝑐𝑐𝑐𝑐𝑐 = − 1302 𝑘𝑘𝐽𝐽𝑚𝑚𝑚𝑚𝑚𝑚 Formation Enthalpies: [9] Which is a formation enthalpy: a) Na + (aq) + NO 3 - (aq) → NaNO 3 (aq) b) Na + (g) + NO 3 - (g) → NaNO 3 (s) c) Na(s) + NO 3 (s) → NaNO 3 (s) d) 2Na(s) + N 2 (g) + 3O 2 (g) → NaNO 3 (s) e) Na(s) + 1/2 N 2 (g) + 3/2O 2 (g) → NaNO 3 (s) [10] Determine the enthalpy change for the following reaction: CH 4 (g) + 2O 2 (g) → 2H 2 O(l) + CO 2 (g) ∆ H f ° CH 4 (g) O 2 (g) H 2 O(l) CO 2 (g) kJ/mol - 75 0 - 572 - 394 � 2 mol×-572 kJ mol + 1 mol×-394 kJ mol � - � 1 mol×-75 kJ mol + 2 mol×0 kJ mol � = -1463 kJ [11] Calculate the standard enthalpy of formation of gaseous diborane (B2H6) using the following thermochemical information: 4 B(s) + 3 O 2 (g) → 2 B 2 O 3 (s) ∆ H ° = -2509.1 kJ 2 H 2 (g) + O 2 (g) → 2 H 2 O(l) ∆ H ° = -571.7 kJ B 2 H 6 (g) + 3 O 2 (g) → B 2 O 3 (s) + 3 H 2 O(l) ∆ H ° = -2147.5 kJ Formation Reaction: 2B(s) + 3H 2 (g) → B 2 H 6 (g) 1 2 � 4B(s) + 3O 2 (g) → 2B 2 O 3 (s) � ∆ H° = 1 2 { -2509.1 kJ } = -1254.6 kJ 3 2 � 2H 2 (g) + O 2 (g) → 2 H 2 O(l) � ∆ H° = 3 2 { -571.7 kJ } = -857.6 kJ � B 2 O 3 (s) +3 H 2 O(l) → B 2 H 6 (g) + 3O 2 (g) � ∆ H° =- { -2147.5 kJ } = 2147.5 kJ ∆ H f = ( -1254.6 kJ ) + ( -857.6 kJ ) + ( 2147.5 kJ ) = 35.4 k 𝐽𝐽