Question

Liquid ammonia (boiling point is –33.4°c) can be used as a refrigerant and heat transfer fluid. how much energy is needed to heat 25.0 g of nh3(l) from –65.0°c to –12.0°c? (specific heat capacity of nh3(l) = 4.7 j/g•k; specific heat capacity of nh3(g) = 2.2 j/g•k; δhvap of nh3 = 23.5 kj/mol)

Answer 1

33.4C - -65C = 31.6 C, that's the degrees K you need to heat it before it vaporizes. 31.6K * 4.7J/gK * 25g = 3713 J, that's the energy to heat it to the boiling point. 23500J/mol * 25g / 17g/mol = 34559 J, that's the energy to change all the ammonia from liquid to vapor. -12C - -33.4C = 21.4 C, that's the degrees K you need to heat it before it gets to the target temperature. 21.4K * 2.2J/gK * 25g = 1177 J, that's the energy to heat it to the target temperature.