Answer to Question #271719 in Physics for Alpha

Question

Exercise 7

1. When 1.5kg of water is converted to steam (at 1000

c) at STP, 3.39MJ of heat are required.

During the transformation from liquid to vapour state, the increase in volume of the water

is 2.5m3

. Calculate the work done against the external pressure during the process of

veporisation. Explain what happens to the rest of energy.

Answer 1

As we know, according to the first law of thermodynamics,

$$Q=\Delta U+W,\\ W=P\Delta V=101325·2.5=0.253\text{ MJ}.$$

The rest of the energy comes to increase the internal energy.