4.1: UNDERSTANDING THERMAL EQUILIBRIUM

1. The net heat will flow from A to B until the temperature of A is the (same, zero) as the temperature of

B. In this situation, the two bodies are said to have reached thermal equilibrium.

2. When thermal equilibrium is reached, the net rate of heat flow between the two bodies is (zero, equal)

3. There is no net flow of heat between two objects that are in thermal equilibrium. Two objects in

thermal equilibrium have the same temperature.

4. The liquid used in glass thermometer should

(a) Be easily seen

(b) Expand and contract rapidly over a wide range of temperature

(c) Not stick to the glass wall of the capillary tube

5. List the characteristic of mercury

(a) Opaque liquid

(b) Does not stick to the glass

(c) Expands uniformly when heated

(d) Freezing point -390C

(e) Boiling point 3570C

6. (Heat, Temperature) is a form of energy. It flows from a hot body to a cold body.

7. The SI unit for (heat, temperature) is Joule, J.

8. ( Heat , Temperature ) is the degree of hotness of a body

9. The SI unit for (heat, temperature) is Kelvin, K.

10. Lower fixed point (l 0 )/ ice point : the temperature of pure melting ice/00C

11. Upper fixed point( l 100)/steam point: the temperature of steam from water that is boiling under

standard atmospheric pressure /1000C

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CHAPTER 4: HEAT

Section B: Answer the questions by showing the calculation1. The length of the mercury column at the ice point and steam point are 5.0 cm and 40.0cm

respectively. When the thermometer is immersed in the liquid P, the length of the mercury column is 23.0 cm. What is the temperature of the liquid P?

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Specific heat capacity, c = Q__ m∆θ

2. The length of the mercury column at the steam point and ice point and are 65.0 cm and 5.0cm respectively. When the thermometer is immersed in the liquid Q, the length of the mercury column is 27.0 cm. What is the temperature of the liquid Q? [Answer: 36.670C ]

4.2: UNDERSTANDING SPECIFIC HEAT CAPACITY

1. The heat capacity of a body is the amount of heat that must be supplied to the body to increase its

temperature by 10C.

2. The heat capacity of an object depends on the

(a) ……………………………………………………………………………………….

(b) ……………………………………………………………………………………….

(c) ………………………………………………………………………………………

3. The specific heat capacity of a substance is the amount of heat that must be supplied to increase the

temperature by 1 0C for a mass of 1 kg of the substance. Unit Jkg-1 0C-1

4. The heat energy absorbed or given out by an object is given by Q = mc∆θ

5. High specific heat capacity absorbs a large amount of heat with only a small temperature increase

such as plastics.

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Temperature of the body

Mass of the body

Type of material

Explain the meaning of above application of specific heat capacity:

(a) Water as a coolant in a car engine

(i) Water is a good example of substance with a high specific capacity. It is used as a cooling agent to

prevent overheating of the engine .Therefore; water acts as a heat reservoir as it can absorb a great

amount of heat before it boils.

(b) Household apparatus and utensils

1. A metal has a low specific heat capacity.

2. Its temperature increases easily when heated.

3. The food or water can be heated faster.

4. This is because only a little amount of heat is needed to heat the metal; therefore more heat is

transferred to the food.

5. Examples : pot, frying-pan, filaments of kettles and others utensils

Think about it: Why the handles of utensils made of materials of high specific heat capacity, c.

SECTION B: Answer all questions by showing the calculation

1. How much heat energy is required to raise the temperature of a 4kg iron bar from 32 0C to 520C? (Specific heat capacity of iron = 452 Jkg-1 0C-1). Amount of heat energy required, Q = mcθ

=

=

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2. Calculate the amount of heat required to raise the temperature of 0.8 kg of copper from 350C to 600C. (Specific heat capacity of copper = 400 J kg-1 C-1).Amount of heat required, Q = mcθ

=

=

3. Calculate the amount of heat required to raise the temperature of 2.5 kg of water from 32 0C to 820C. (Specific heat capacity of water = 4200 J kg-1 C-1).Amount of heat required, Q = mcθ

=

=

4. 750g block of a aluminium at 1200C is cooled until 450C. Find the amount of heat is released. . (Specific heat capacity of aluminium = 900 J kg-1 C-1).Amount of heat released, Q = mcθ

=

=

5. 0.2 kg of water at 700C is mixed with 0.6 kg of water at 300C. Assuming that no heat is lost, find the final temperature of the mixture. (Specific heat capacity of water = 4200 J kg-1 C-1)Amount of heat released, Q = Amount of heat required, Q

mcθ = mcθ

4.3 UNDERSTANDING SPECIFIC LATENT HEAT

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4.4 UNDERSTANDING THE GAS LAW

1. The kinetic theory of gas is based on the following assumptions:

(a) The molecules in a gas move freely in random motion and posses kinetic energy

(b) The forces of attraction between the molecules are ignored.

(c) The collisions of the molecules with each other and with the walls of the container are elastic

collisions.

4.4.1 Boyle’s Law

1. Boyle’s law states that for a fixed mass of gas, the pressure of the gas is inversely proportional to its

volume when the temperature is kept constant.

2. Boyle’s law can be shown graphically as in Figure above

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θ/0C100-273

1. Charles’ law states that for a fixed mass of gas, the volume of the gas is directly proportional to its

absolute temperature when its pressure is kept constant.

2. The temperature -2730C is the lowest possible temperature and is known as the absolute zero of

temperature.

3. Fill the table below.

Temperature Celsius scale (0C) Kelvin Scale(K)

Absolute zero -273 0

Ice point 0 273

Steam point 100 373

Unknown point θ ( θ + 273 )

4. Complete the diagram below.

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0

P/Pa

1. The pressure law states that for a fixed mass of gas, the pressure of the gas is directly proportional to

its absolute temperature when its volume is kept constant.

EXERSICE 4.4Gas Law

1. A mixture of air and petrol vapour is injected into the cylinder of a car engine when the cylinder volume

is 100 cm3. Its pressure is then 1.0 atm. The valve closes and the mixture is compressed to 20 cm 3. Find

the pressure now.

2. The volume of an air bubble at the base of a sea of 50 m in deep is 200 cm 3. If the atmospheric pressure

is 10 m of water, find the volume of the air bubble when it reaches the surface of the sea.

3. The volume of an air bubble is 5 mm3 when it is at a depth of h m below the water surface. Given that

its volume is 15 mm3 when it is at a depth of 2 m, find the value of h. (Atmospheric pressure = 10 m of

water)

4. An air bubble has a volume of V cm3 when it is released at a depth of 45m from the water surface. Find

its volume (V) when it reaches the water surface. (Atmospheric pressure = 10 m of water)

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5. A gas of volume 20m3 at 370C is heated until its temperature becomes 870C at constant pressure. What is

the increase in volume?

6. The air pressure in a container at 330C is 1.4 X 1O5 N m-2. The container is heated until the temperature

is 550C. What is the final air pressure if the volume of the container is fixed?

7. The volume of a gas is 1 cm3 at 150C. The gas is heated at fixed pressure until the volume becomes triple

the initial volume. Calculate the final temperature of the gas.

8. An enclosed container contains a fixed mass of gas at 250C and at the atmospheric pressure. The

container is heated and temperature of the gas increases to 980C. Find the new pressure of the gas if the

volume of the container is constant.(Atmospheric pressure = 1.0 X 105N rn2)

9. The pressure of a gas decreases from 1.2 x 105 Pa to 9 x 105 Pa at 400C. If the volume of the gas is

constant, find the initial temperature of the gas.

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