Ch 10 Thermal Properties of Matter

Question 1

What is temperature?

Answer 1

Temperature is a measure of how hot or cold a body is.

Question 2

What is the internal energy of a body?

Answer 2

Internal energy is the sum of the total kinetic energy and potential energy of molecules in the body.

Question 3

Define melting. (the process)

Answer 3

Melting is a process whereby energy is supplied to change the state of a substance from solid to liquid, without a change in temperature.

Question 4

Define freezing. (the process)

Answer 4

Freezing is a process whereby energy is removed to change the state of a substance from liquid to solid , without a change in temperature.

Question 5

Define boiling . (the process)

Answer 5

Boiling is a process whereby energy is supplied to change the state of a substance from liquid to gas, without a change in temperature.

Question 6

Define condensation. (the process)

Answer 6

Condensation is a process whereby energy is removed to change the state of a substance from gas to liquid , without a change in temperature.

Question 7

Define evaporation. (the process)

Answer 7

Evaporation is a process whereby water changes into vapour without boiling.

Question 8

State 4 differences between evaporation and boiling.

Answer 8

Boiling

Evaporation

quick

slow

bubbles formed

no bubbles

occurs throughout the liquid

occurs at surface of liquid only

occurs at one temperature – boiling point

occurs at any temperature between melting and boiling point

Question 9

Explain how cooling occurs by evaporation.

(Using kinetic model of matter)

Answer 9

1) When evaporation occurs, the faster-moving molecules escape from the surface of the liquid, leaving behind the slower-moving molecules.
2) The average speed of the molecules left behind will decrease and thus the average kinetic energy of the molecules left behind will decrease.
3) This makes the temperature of the liquid drops and cooling occurs.

Question 10

State 6 factors that affect the rate of evaporation.

Answer 10

1) temperature of the liquid
2) area of exposed surface of liquid
3) humidity of surrounding air
4) motion of air (presence of wind)
5) pressure of surrounding air
6) nature of liquid (boiling point of liquid)