For heating 500 g of water and converting 100 g of it into steam, 420 kJ of heat was spent.

For heating 500 g of water and converting 100 g of it into steam, 420 kJ of heat was spent. What is the initial water temperature?

Initial data: m1 (heating) = 500 g = 0.5 kg; m2 (vaporization) = 100 g = 0.1 kg; Q (spent heat) = 420 kJ = 420 * 10 ^ 3 J.

Reference values: tboil (boiling point) = 100 ºС; C (specific heat capacity) = 4200 J / (kg * K); L (beats heat of vaporization) = 2.3 * 10 ^ 6 J / kg.

Q = C * m1 * (tboil – t0) + L * m2.

C * m1 * (tboil – t0) = Q – L * m2.

tboil – t0 = (Q – L * m2) / C * m1.

t0 = tboil – (Q – L * m2) / C * m1 = 100 – (420 * 10 ^ 3 – 2.3 * 10 ^ 6 * 0.1) / (4200 * 0.5) = 9.52 ºС …