Question

How much heat energy is released when 5g of water at 20 o c changes into ice at 0 o c . Take specific heat capacity of water 4.2 J g -1 o c -1 . and specific latent heat of fusion of ice 336 J/g.

Answer 1

Heat released = Heat to change temp from 20°C to 0° + Latent Heat of fusion
                       =mcΔt + mL

Heat released = 5×4.2×(20) +5×336
                       =420+ 1680
                       = 2100 J

Answer 2

Answer:

Explanation:

Given,

5g of water at 20° C changes into ice at 0° C .

or, Δt = 20-0 = 20°C

specific heat capacity of water = s = 4.2 J /g °C

Specific latent heat of fusion of ice = L = 336 J/g.

Total heat released will be equal to the sum of heat released to change temperature of water from 20°C to 0°C and heat relased to change its state from water to ice i.e specific latent heat of fusion.

H = msΔt + mL

or, H= 5 × 4.2 × 20 + 5 × 336

or, H = 420 + 1680

or, H = 2100 joule

Therefore, Total heat energy released = 2100 J