Problem 6 nitrogen evaporates if it is at its boiling point of 77 K and has a la
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Question
Problem 6 nitrogen evaporates if it is at its boiling point of 77 K and has a latent heat of vaporization of 200 ki/kg? Assume for simplicity that the specific heat of ice is a constant and is equal to its value near its melting Problem 7 Indicate whether the following heat transfers are conduction, convection or radiation. a) Steam rising from a cup of hot coffee b) Warming your back muscles with a heating pad. c) Microwaves from a microwave oven. d) Chocolate candy melting in your hand 19 F7 FS eenh BackspaExplanation / Answer
6)
specific heat of ice is 2.06 kJ/kgC
Ice has to cool from 0C to –195.79C, so the energy removed is
E = 2.06 kJ/kgC x 0.015 kg x 195.8 C = 6.05 kJ
how much N2 evaporates with that energy
6.05 kJ = 200 kJ/kg x M
M = 0.03025 kg or 30.25 g