Week 41. 2 3 4 It’s 5 o C and about 1 atm outside today. If you wanted to make water vapor, how would you do it?

Week 4 1

Week 4 2

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Week 4 3

Week 4 4

It’s 5oC and about 1 atm outside today. If you wanted to make water vapor, how would you do it?

Week 4 5

There are some hot air balloons that can reach near-space altitudes.

If you take a glass of water up with you in one of these balloons, what will happen? (Assume the temperature doesn’t change much on the ascent.)

Week 4 6

Week 4 7

Assuming you don’t have to change the temperature, which takes more energy: vaporizing water or vaporizing lead?

Week 4 8

Why does sweating cool you down?

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Week 4 9

The maximum amount of water an adult in temperate climates can perspire in one hour is typically 1.8 L. However, after several weeks in a tropical climate the body can adapt, increasing the maximum perspiration rate to 3.5 L/hr.

At what rate is energy being removed when perspiring that rapidly? Assume all of the perspired water evaporates. At body temperature, Lv=24x105J/kg for water.

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Week 4 10

How much heat do you need to remove to make 1 kg of nitrogen from the air into liquid nitrogen?

cnitrogen gas = 1040 J/kg/K

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Week 4 11

Week 4 12

• To understand phase changes as processes in which energy is transferred to a system without the temperature increasing, and to understand the concept of latent heat.

• To determine the latent heats of fusion and vaporization of water.

• To understand the meaning of internal energy of a system.

• To understand the energy balance of a system between heat energy transfer, work done, and changes in the internal energy, as described by the first law of thermodynamics.

LAB 4 OBJECTIVES:

Week 4 13

You put a block of frozen soup into a pot on the stove. The stove transfers heat to your soup at a constant rate until it has not only thawed but heated to the boiling point.

Graph the temperature of the soup from the time you first put it on the stove frozen to some time after it has started to boil. Label any phase changes.

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