Question

1 g of a steam at 100°C melt how much ice at 0°C? (Latent heat of ice = 80 cal/gm and latent heat of steam = 540 cal/gm)

• A. 1 gm
• B. 2 gm
• C. 4 gm
• D. 8 gm

Answer 1

Answer: (D)

8 gm

Answer 2

Suppose m gm ice melted, then heat required for its melting $= mL = m \times 80cal$

Heat available with steam for being condensed and then brought to 0°C

$= 1 \times 540 + 1 \times 1 \times (100 - 0) = 640cal$

⇒ Heat lost = Heat taken

⇒ $640 = m \times 80$ ⇒ $m = 8gm$

Short trick: You can remember that amount of steam (m') at 100°C required to melt m gm ice at 0°C is $m' = \frac{m}{8}$.

Here, $m = 8 \times m' = 8 \times 1 = 8gm$