Question

How much heat energy is released when 5.0 g of water at 20℃ changes into ice at 0℃? Take specific heat capacity of water = 4.2 J g^-1 K^-1, Specific latent heat of fusion of ice = 336 J g^-1.

Answer 1

Given,

Mass (m) = 5.0 g

Specific heat capacity of water (c) = 4.2 J g^-1 K^-1

Specific latent heat of fusion of ice (L) = 336 J g^-1

(i) Heat energy released when water lowers it's temperature from 20° C to 0° C

= m × c × change in temperature

Substituting the values in the formula we get,

Q₁ = 5 × 4.2 × (20 − 0)

Q₁ = 5 × 4.2 × 20

⇒ Q₁ = 420 J

(ii) Heat energy released when water at 0° C changes into ice at 0° C = m × L

Substituting the values in the formula we get,

Q₂ = 5 × 336 J

⇒ Q₂ = 1680 J

From relation,

Q = Q₁ + Q₂

Q = 420 + 1680

Q = 2100

Total heat released = 2100 J