Thermal Properties Of Matter

Question 0

What is internal energy?

Answer 0

Sum of KE and PE of atoms in body.

Question 1

Define ‘Random thermal energy’.

Answer 1

Total kinetic energy molecules have in a body.

Question 2

What happens to the internal energy of body as temperature increases?

Answer 2

Internal energy increases.

Question 3

What is heat capacity C?

Answer 3

Amount of thermal energy required to raise temperature of object by 1 degree or 1K.

Question 4

What is specific heat capacity?

Answer 4

Amount of thermal energy required to raise temperature of 1kg of material by 1 degree or 1K.

Question 5

Why does water have a high specific capacity?

Answer 5

Able to absorb a lot of heat before its temperature rises by 1 degree.

Question 6

What is an example of water being a good cooling agent?

Answer 6

Radiator of car engine.

Question 7

What is an example of water being a good heating agent?

Answer 7

Hot water bottle able to keep patient warm.

Question 8

What are some materials with low specific heat capacities?

Answer 8

Metals like copper and steel.

Question 9

Why do metals have low specific heat capacities?

Answer 9

Very little energy required to heat up cooking utensils.

Question 10

What happens when a solid melts?

Answer 10

1. Heat absorbed, but temperature of substances remains unchanged.
2. Heat absorbed known as latent heat of fusion.

Question 11

What happens during freezing?

Answer 11

1. Liquid changes into solid.

2. Latent heat of fusion released, temperature remains unchanged.

Question 12

Why does the temperatures of ice remains constant when it melts?

Answer 12

1. When ice melts, thermal energy supplied(LHOF) causes internal energy of water molecules to increase.
2. Since temp constant at 0, KE remains unchanged.
3. PE changed due to change in separation between molecules.

Question 13

What are the factors affecting melting point of water?

Answer 13

1. Addition of impurities like ice. Lowers MP of water to below 0.
2. Increase in pressure reduces MP of ice.

Question 14

What happens when liquid boils?

Answer 14

1. Thermal energy transferred to liquid without temp change.
2. Latent heat of vaporization absorbed by liquid to change to vapor at its BP.

Question 15

What happened during condensation?

Answer 15

Vapor changes into liquid at constant temp.

Question 16

What are some factors affecting BP of water?

Answer 16

1. BP of water increase when salt added.
2. BP increase above 100 when external pressure increase.
3. Water boils below 100 when pressure above water decreases.

Question 17

What are some applications of boiling water under reduced pressure?

Answer 17

1. Refining of cane sugar at low pressure saves fuel costs.

2. Evaporated milk produced by boiling milk under reduced pressure at low temp so vitamins not destroyed by heat.

Question 18

What happens during evaporation?

Answer 18

1. Liquid molecules that have KE escape from liquid surface.
2. Molecules remaining in liquid have lower KE.
3. Hence temp of liquid lowers.

Question 19

What is an example of evaporation producing a cooling effect?

Answer 19

1. Hand rubbed with ethanol feels cool because ethanol evaporates rapidly.
2. Heat required for evaporation is absorbed by hand.

Question 20

Give an example of application of cooling by evaporation.

Answer 20

1. When seating occurs, heat absorbed by body.

2. This cools down body.

Question 21

What are the factors affecting rate of evaporation?

Answer 21

1. Surface area
2. Temperature
3. Humidity
4. Wind

Question 22

How does surface area affect rate of evaporation?

Answer 22

1. Bigger surface area
2. More molecules on surface
3. More molecules able to escape.

Question 23

How does temperature affect rate of evaporation?

Answer 23

1. Higher temp = higher KE.

2. More molecules able to escape.

Question 24

How does humidity affect rate of evaporation?

Answer 24

1. High humidity = higher amt water vapor in air(above liquid).
2. Liquid molecules that escape can collide with water molecules in air and return back.

Question 25

How does wind affect rate of evaporation?

Answer 25

1. When there is breeze.
2. Breeze blow away water molecules that evaporate.
3. When space above liquid surface is clear of vapor, subsequent liquid molecules that escape from liquid will not be knocked back into liquid.

Question 26

What are the differences between boiling and evaporation?

Answer 26

1. B at fixed temperature. E at ALL temp below BP.
2. B take place throughout whole liquid, E only at liquid surface.
3. B faster rate, E slower rate.
4. B causes bubbles, E no bubbles.

Question 27

What is latent heat L of a substance?

Answer 27

Thermal energy transferred when substances changes from one state to another at constant temp.

Question 28

What is specific latent heat l?

Answer 28

Thermal energy transferred when unit mass of substances changes from one state to another at constant temp.