How much water taken at a temperature of 20 degrees can be evaporated by giving it 1.2 MJ of heat?

To calculate the mass of water converted into steam, we will use the formula: Q = L * m + Cw * m * (tboil – t0), from where we express: m = Q / (L + Cw * (ti – t0)).

Variables and constants: Q – heat transferred to water (Q = 1.2 MJ = 1.2 * 10 ^ 6 J); L is the heat of vaporization of water (L = 2.3 * 10 ^ 6 J / kg); Cw – heat capacity of water (Cw = 4200 J / (kg * K)); ti – temperature of the beginning of evaporation (ti = 100 ºС); t0 – initial temperature (t0 = 20 ºС).

Calculation: m = 1.2 * 10 ^ 6 / (2.3 * 10 ^ 6 + 4200 * (100 – 20)) = 0.455 kg.