Ethanol (C2H5OH) melts at -114 °C. The enthalpy of fusion is 5.02 kJ/mol. The specific heats of solid and liquid ethanol are 0.97 J/g-K and 2.3 J/g-K, respectively. How much heat (kJ) is needed to convert 25.0 g of solid ethanol at -135 °C to liquid ethanol at -50 °C?

Answer 1

Heat needed = (25.0 g)(5.02 kJ/mol)(1000 J/kJ)(1 mol/46.07 g)(1 - (-50 °C)/(-114 °C)) + (25.0 g)(2.3 J/g-K)(-85 °C) = -7.7 kJ