Question

A steam engine intakes $50\ g$ of steam at $100°C$ per minute and cools it down to $20°C$. If latent heat of vaporization of steam is $540\ cal\ g^{–1}$, then the heat rejected by the steam engine per minute is ______ $× 10^3$ $cal.$
(Given : specific heat capacity of water : $1\ cal \ g^{–1} °C^{–1}$)

Answer 1

$ΔQ_{rej} = 50 × 540 + 50 × 1 × (100 – 20)$
$ΔQ_{rej} = 50 × [540 + 80]$
$ΔQ_{rej} = 50 × 620$
$ΔQ_{rej}= 31000\ cal$
$ΔQ_{rej} = 31 × 10^3\ cal$

So, the answer is $31$.