Question

Find the amount of heat released if $1kg$ steam at ${200}^{\circ }C$ is converted into $-{20}^{\circ }C$ ice.

• A. $680kcal$
• B. $600kcal$
• C. $780kcal$
• D. $700kcal$

Answer 1

Answer: (C)

$780kcal$

Heat released by steam is $=$ heat released when it is cooled to ${100}^{o}C+$ latent heat $+$ heat released when it is cooled to $0^{o}C$ $+$ latent heat of fusion.

$Q=[1\times 0.5\times (200-100\left)\right]+[540\times 1]+[1\times 1\times (100-0\left)\right]+[80\times 1]+[1\times 0.5\times (0-(-20)\left)\right]=780kcal$