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GCE O level Pure Physics 6091 > 11) Thermal Properties of Matter > Flashcards

11) Thermal Properties of Matter Flashcards

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1
Q

What is temperature?

A

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

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2
Q

What is the internal energy of a body?

A

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

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3
Q

Define melting. (the process)

A

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

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4
Q

Define freezing. (the process)

A

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

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5
Q

Define boiling . (the process)

A

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

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6
Q

Define heat capacity of a substance.

A

Amount of heat needed by the substance to produce one unit change in temperature.

e.g.

heat capacity of 2 kg of water is 8400 J / oC

8400 J of heat is needed to raise the temperature of 2 kg of water by 1 oC.

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7
Q

Define specific heat capacity of a substance.

A

Amount of heat needed by the substance to change a unit temperature per unit mass.

e.g.

specific heat capacity of water is 4200 J / oC kg

4200 J of heat is needed to raise the temperature of 1 kg of water by 1 oC.

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8
Q

What is the relationship between thermal energy Q, mass m, specific heat capacity c and the change in temperature ΔT?

A

Q = mcΔT

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9
Q

Define condensation. (the process)

A

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

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10
Q

Define evaporation. (the process)

A

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

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11
Q

State 4 differences between boiling and evaporation.

A

Boiling

  1. quick
  2. bubbles formed
  3. occurs throughout the liquid
  4. occurs at one temperature – boiling point

Evaporation

  1. slow
  2. no bubbles
  3. occurs at surface of liquid only
  4. occurs at any temperature between melting and boiling point
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12
Q

Define latent heat.

A

Latent heat is the thermal energy absorbed or released during a change in state.

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13
Q

Define specific latent heat of vaporisation of a substance.

A

The heat that is absorbed without any change in temperature when the substance is boiling is called the latent heat of vaporization.

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14
Q

Define specific latent heat of fusion of substance.

A

The thermal energy that is absorbed withour a change in temperature when the substance is melting is called the latent heat of fusion of the substance.

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15
Q

Explain how cooling occurs by evaporation.

(Using kinetic model of matter)

A
  • When evaporation occurs, the faster-moving molecules escape from the surface of the liquid, leaving behind the slower-moving molecules in the liquid.
  • The average speed of the molecules left behind will decrease and thus the average kinetic energy of the molecules left behind will decrease.
  • This makes the temperature of the liquid drops and cooling occurs.
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16
Q

State 6 factors that affect the rate of evaporation.

A

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)

17
Q

What is the relationship between thermal energy Q, mass m, and the latent heat of vaporisation lv?

A

Q = mlv

18
Q

What is the relationship between thermal energy Q, mass m, and the latent heat of fusion lf?

A

Q = mlf

19
Q

Explain latent heat of vaporisation during boiling in terms of molecular behaviour.

A
  • During boiling, the gain in thermal energy (latent heat of vaporization) is used to overcome the forces of attraction between the molecules of liquid and separate the molecules further apart.
  • The average kinetic energy of the molecules does not change and thus temperature remains constant during boiling.
20
Q

Explain latent heat of vaporisation during condensation in terms of molecular behaviour.

A
  • During condensation, the forces of attraction between the gas molecules get stronger as they come together and release thermal energy (latent heat of vaporization).
  • The kinetic energy of the molecules remains unchanged and thus the temperature remains constant during condensation.
21
Q

Explain latent heat of fusion during melting in terms of molecular behaviour.

A
  • During melting, the gain in thermal energy (latent heat of fusion) is used to overcome the forces of attraction between the molecules of solid.
  • The kinetic energy of the molecules remains unchanged and thus the temperature remains constant during melting.
22
Q

Explain latent heat of fusion during freezing in terms of molecular behaviour.

A
  • During freezing, the forces of attraction between the liquid molecules get stronger as they come together and release thermal energy (latent heat of fusion).
  • The kinetic energy of the molecules remains unchanged and thus the temperature remains constant during freezing.
23
Q

Interpreting a cooling curve:

The diagram shows the cooling curve of liquid naphthalene.

What is the state of naphthalene at AB?

A

liquid

24
Q

Interpreting a cooling curve:

The diagram shows the cooling curve of liquid naphthalene.

What is the state of naphthalene at AB?

A

liquid

25
Q

Interpreting a cooling curve:

The diagram shows the cooling curve of liquid naphthalene.

What is the state of naphthalene at BC?

A

mixture of liquid and solid

26
Q

Interpreting a cooling curve:

The diagram shows the cooling curve of liquid naphthalene.

What is the state of naphthalene at CD?

A

solid

27
Q

Interpreting a cooling curve:

The diagram shows the cooling curve of liquid naphthalene.

What is the melting point of naphthalene?

A

80 oC

GCE O level Pure Physics 6091 (18 decks)

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