10. CaO (s) reacts with water to form Ca(OH)2(aq). If 6.50 g CaO is combined wit

Question

10. CaO (s) reacts with water to form Ca(OH)2(aq). If 6.50 g CaO is combined with 99.70 g H20 in a coffee cup calorimeter, the temperature of the resulting solution increases from 21.7°C to 431°C. Calculate the enthalpy change for the reaction per mole of CaO. Assume that the specific heat capacity of the solution is 4.18 J/g.K. (a) -1.45 kJ/mol (b) -82.0 kJ/mol (c) -9.42 kJ/mol (d) -165 kJ/mol (e) -532 kJ/mol 11. A bomb calorimeter has a heat capacity of 2.47 kJ/K. When a 0.120-g sample of ethylene (C2Hs) was burned in this calorimeter, the temperature increased by 2.44 K. Calculate the enthalpy change per mole of ethylene combusted. (a) -5.29 k.I/mol

Explanation / Answer

10

mass of solution(m) = 6.5+99.7 = 106.2 g

s = specific heat of solution = 4.18 j/g.k

DT = 43.1-21.7 = 21.4 c

heat released(q) = m*s*DT

                 = 106.2*4.18*21.4

                 = 9.5 kj

no of mol of CaO reacted = 6.5/56 = 0.116 mol

DHrxn = -q/n = -9.5/0.116 = -81.9 kj/mol

answer: b) - 82.0 kj/mol

11
No of mol of ethylene = w/M = 0.12/28 = 0.0043 mol

heat released(q) = C*DT

                  = 2.47*2.44

                  = 6.03 kj

DHrxn = -q/n

       = -6.03/0.0043

       = -1402.3 kj/mol

answer: - 1402 kj/mol

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