Acetylene (C2H2) and a hydroxide can be made by reacting calcium carbide (CaC2)

Question

Acetylene (C2H2) and a hydroxide can be made by reacting calcium carbide (CaC2) with water. (a) Write a balanced equation for the reaction (b) What is the maximum amount of heat (in joules) that can be obtained from the combustion of acetylene, starting with 61.4g CaC2? delta H formation (CO2) = -393.5 kJ/mol delta H formation (C2H2) = 226.6 kJ/mol delta H formation (H2O) = -285.8 kJ/mol

Explanation / Answer

CaC2 + 2H2O ? C2H2 + Ca(OH)2 CaC2 + 2H2O >> C2H2 + Ca(OH)2 32 / 64.1 g/mol =0.499 moles of CaC2 Moles H2O = 2 x 0.499 = 0.998 Mass water = 0.998 mol x 18.02 g/mol = 18.0 g Moles C2H2 produced = 0.499 Mass C2H2 = 0.499 mol x 26.038 g/mol =13.0 g PV =nRT R = 0.08206 L atm mol-1 K-1 T= 273.2 + 25 = 298.2 K Actual pressure of C2H2: P(measured) - P(H2O vap) = 721 - 23.8 torr = 697.4 torr Need to convert to atm = 697.4/760 = 1.090 atm V =nRT/P = (7.488*10^-2* 0.08206*298.2)/1.090 = 1.68 L (3 sig figs)

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