A 75 g ice cube at its melting point is dropped into an insulated container of l

Question

A 75 g ice cube at its melting point is dropped into an insulated container of liquid nitrogen.

Part A

How much nitrogen evaporates if it is at its boiling point of 77 K and has a latent heat of vaporization of 200 kJ/kg ? Assume for simplicity that the specific heat of ice is a constant and is equal to its value near its melting point.

A 75 g ice cube at its melting point is dropped into an insulated container of liquid nitrogen.

Part A

How much nitrogen evaporates if it is at its boiling point of 77 K and has a latent heat of vaporization of 200 kJ/kg ? Assume for simplicity that the specific heat of ice is a constant and is equal to its value near its melting point.

Explanation / Answer

specific heat of ice is 2.06 kJ/kgC

Ice has to cool from 0C to –195.79C (converted from K to C), so the energy removed is :

E = 2.06 kJ/kgC x 0.075 kg x 195.8 C = 30.24 kJ

how much N2 evaporates with that energy

30.24 kJ = 200 kJ/kg x M

M = 30.24/200

M = 0.151 kg or 151 g (ans)

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