Cooling with Liquid Nitrogen & Melting Aluminum Cans: Energy Calculations

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Homework Help Overview

The discussion revolves around energy calculations related to cooling with liquid nitrogen and melting aluminum cans. The original poster presents two distinct problems involving the energy required for phase changes and temperature changes in specific materials.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the need to provide attempted solutions when seeking help. There are questions about the amount of homework completed and the effort reflected in the answers provided.

Discussion Status

The discussion includes some light-hearted commentary regarding the effort put into homework. Participants have not reached a consensus on the problems, and there is an emphasis on the importance of showing work when asking for assistance.

Contextual Notes

There is an implied expectation for participants to demonstrate their attempts at solving the problems before receiving help, which may influence the nature of the responses and guidance offered.

mustang
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Problem 2. Liquid nitrogen, which has a boiling point of
77 K, is commonly used to cool substances to
low temperatures.
How much energy must be removed from
1.4 kg of gaseous nitrogen at 77 K for it to
completely liquefy? Assume the latent heat
of liquid nitrogen is 2.01 *10^5 J/kg Answer
in units of J.

Problem 4.
You have collected exactly 2200 aluminum
cans for recycling, each with a mass of 14.1 g.
How much energy is needed to melt them if
their initial temperature is 26.8 degrees C? Assume
the specific heat, the latent heat and the
melting point of aluminum are 899 J/kg * degrees C,
3.97*10^5 J/kg and 660.4degreesC respectively. An-
swer in units of J.
 
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Mustang,

You've been here long enough to know you should post what you've tried when asking for help.
 
how much homework have you done...
 
1600J and 3200J

The answers reflect how much effort you put into trying to solving your homework :-p
 

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