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Problem 1.41. To measure the heat capacity of an object, all you usually have to do is put it in thermal contact with another object whose heat capacity you know. As an example, suppose that a chunk of metal is immersed in boiling water (100掳C), then is quickly transferred into a Styrofoam cup containing 250 g of water at 20掳C. After a minute or so, the temperature of the contents of the cup is 24掳C. Assume that during this time no significant energy is transferred between the contents of the cup and the surroundings. The heat capacity of the cup itself is negligible.

  1. How much heat is lost by the water?
  2. How much heat is gained by the metal?
  3. What is the heat capacity of this chunk of metal?
  4. If the mass of the chunk of metal is 100 g, what is its specific heat capacity?

Short Answer

Expert verified
  1. The heat gained by water is 1000 cal.
  2. -1000 cal.
  3. 13.157鈥塩补濒.碍-1
  4. The specific heat of 100 g of a chunk of the metal is c=0.131cal.g-1K-1.

Step by step solution

01

Part a. Step 1. Given.

Mass of water,m=250g

Specific heat of water,c=1鈥塩补濒.驳-1K-1

Initial temperature,T1=240C

Final temperature,T2=200C

02

Part a. Step 2. Calculation.

The first energy transfer takes place between the chunk of metal and the boiling water at temperature 1000C. The next energy transfer takes place between the metal and the water in the Styrofoam cup that was at temperature 200C.

The heat absorbed Qby the water from the hot metal is given by the expression,

Q=mcT2T1Q=25014Q=1000鈥塩补濒

03

Part a. Step 3. Conclusion.

The only energy transfer is heat transfer, thus the heat absorbed by the water is 1000 cal.

04

Part b. Step 1. Introduction.

Heat capacity 鈥 It is defined as the ratio of heat absorbed to the change in the temperature.

Specific heat 鈥 It is the heat that is needed to raise the temperature of a unit mass to10C.

Energy transfer between two bodies is due to the difference in temperature of the bodies.

05

Part b. Step 2. Explanation.

The heat transfer takes place until the two bodies acquire an equilibrium state and the amount of heat absorbed by water is equal to the heat lost by the metal.

06

Part b. Step 3. Conclusion.

The heat lost by the metal is the heat absorbed by the water, that is -1000 cal.

07

Part c. Step 1. Given.

Initial temperature,T1=1000C

Final temperature,T2=240C

Amount of energy gained by the chunk,Q=1000cal

08

Part c. Step 2. Calculation.

The heat capacity of the metal is given by the expression,

C=QT2T1C=100024100=100076=13.157calK-1

09

Part c. Step 3. Conclusion.

The heat capacity of the metal chunk is calculated as C=13.157cal.g-1K-1.

10

Part d. Step 1. Given.

Heat capacity of the metal,C=13.157calK-1

Mass of the metal,m=100鈥塯

11

Part d. Step 2. Calculation.

c=Cmc=13.157100c=0.131cal.g-1K-1

12

Part d. Step 3. Conclusion.

Specific heat capacity of the 100 g mass of metal is calculated as c=0.131cal.g-1K-1.

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Most popular questions from this chapter

Put a few spoonfuls of water into a bottle with a tight lid. Make sure everything is at room temperature, measuring the temperature of the water with a thermometer to make sure. Now close the bottle and shake it as hard as you can for several minutes. When you're exhausted and ready to drop, shake it for several minutes more. Then measure the temperature again. Make a rough calculation of the expected temperature change, and compare.

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Imagine some helium in a cylinder with an initial volume of 1 liter and an initial pressure of 1 atm. Somehow the helium is made to expand to a final volume of 3 liters, in such a way that its pressure rises in direct proportion to its volume.

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