Question

3. 1.0 kg of water is contained in a 1.25 kW kettle.
Calculate the time taken for the temperature of water
to rise from 25°C to its boiling point 100°C. Specific
heat capacity of water = 4.2 J 9-1 K-1.​

Answer 1

Hey there!

Heat energy required for 1 kg of water to raise its temperature from 25°C to 100°C = mCΔt

here,

m = 1 kg = 1000 g

C = 4.2 J/( g . K)

Δt = 100° - 25° = 75°

Heat required = 1000 * 4.2 * 75 = 315000 J

Now,

Power = 1.25 kW = 1250 W

Power = Heat / time

1250 = 315000 / t

t = 315000 / 1250

t = 252 sec

t = 252 / 60 minute

t = 4.2 min

t = 4 min 2 sec