Question

2 kg ice at – 20⁰C is mixed with 5 kg water at 20⁰C in an insulating vessel having negligible heat capacity. Calculate the final mass of water remaining in container.

Given sp. heat water = 4.186 kJ K^–1 kg^–1

sp. heat Ice = 2.092 kJ K^–1 kg^–1

Latent heat of fusion of ice = 334.7 kJ Kg^–1

• A. 7 kg
• B. 6 kg
• C. 4 kg
• D. 2 kg

Answer 1

Answer: (B)

6 kg

Answer 2

Heat that can be given to ice by water

= 5 kg × 1 × (20 – 0)

Q = 100 k cal.

Energy required to raise temp of ice from – 20⁰C to 0⁰C

E = 2 kg × 0.5 × (0 – ( – 20) = 20 k cal.

Heat available for = Q – E

Melting ice = 100 – 20 = 80 k cal.

L = 80 cal/gram

Ice that can be melted =$\frac{80kcal}{80cal}$= 1000 gram = 1 kg.

Hence water left in container = 6 kg