Question

Inventor jockey will in a way heat a pot of water by freezing one
other amount of water.
a) He wants to heat 1.5 kg of water from 0.0 to 80.0 ºC in a closed and well insulated
container. How much water at 0.0 ºC does he then have to freeze?
b) Does the invention contradict the first theorem of thermodynamics? Motivate your answer.

Answer 1

(a)

The specific heat capacity of water is 4,200 J/kg°C.

to heat 1.5 kg of water from 0.0 to 80.0 ºC ,

energy required = mass of water specific heat capacity of water T

= 1.5 4200 80

= 5.04 10⁵ J

This energy we will get by freezing the ice.

Q = m × L

Where

L = specific latent heat of fusion = 3.336 x 10⁵ J/kg

Therefore,

5.04 10⁵ = mass of water L

5.04 10⁵ = mass of water 3.336 x 10⁵

mass of water = 1.51 kg

(b) No, the invention does not contradict the first theorem of thermodynamics,

because here energy is neither being created nor destroyed, it has been converted from one form to another.

which is the statement of 1st law of thermodynamics.