4.2 Understanding Specific Heat Capacity

Learning Outcomes define specific heat capacity state that

determine the specific heat capacity of a liquid determine the specific heat capacity of a solid Describe applications of specific heat capacity Solve problems involving specific heat capacity

Qcm

Which pot of water take a longer time to boil ?

Requires more heat

Requires less heat

Greater heat capacity Smaller heat capacity

What is heat capacity?

Heat capacity of a body is the amount of heat that must be supplied to the body to increase its temperature by 1oC

18 000 J of heat

4 kg

o = 30oC

1 = 35oC

31 200 J of heat

Which object has a higher heat capacity ?o = 30oC

1 = 38oC

30 kg

18000/5=3600 J oC-1

31 200/8=3900 J oC-1

Higher heat

capacity

What is specific heat capacity?

Specific heat capacity of a body is the amount of heat that must be supplied to increase its temperature by 1oC for a mass of 1 kg of the body.

18 000 J of heat

4 kg

o = 30oC

1 = 35oC

31 200 J of heat

Which object has a higher specific heat capacity ?

o = 30oC

1 = 38oC

30 kg

18000/(5x 4)=900 J kg-1 oC-1

31 200/(8x 30)=130 J kg-1 oC-1

Higher specific heat

capacity

Formulae

Specific heat capacity,Qcm

Quantity of heat absorbed or lost , Q = mc

Heat conductor is easy to be heated up and easy to lose heat . Conductor has a low specific heat capacity.

Heat insulator is more difficult to be heated up and more difficult to lose heat . Insulator has a high specific heat capacity.

Worked example pg 113

The bulb of a thermometer contains 3.4 g of mercury. What amount of heat is required to raise the temperature of the mercury from 30oC to 100o C ?

There is a change of temperature.

What formula to

use ?

Q = mc

Hint :

Ans : 33 J

Worked example pg 114

320 g pf hot water at 80oC is poured into an aluminium can of mass 35 g and temperature of 20oC. Calculate the final temperature.

Specific heat capacity of water= 4200 J kg-1 oC-1

Specific heat capacity of aluminium = 900 J kg-1 oC-1

Let the final temperature be

Heat lost by water = heat gained by aluminium can

(0.320)(4200)(80-) = (0.035)(900)(-20)

107520 - 1344 = 31.5 - 630

1375.5 = 108150

= 78.63oC

Q = mc

80oC

20oC

Application of specific heat capacity

Cooking pot

- Low specific heat capacity so

that the base becomes hot very quickly.

- High density so that the base is heavy and the pot is stable.

Copper base

- Low specific heat capacity so

that the pot becomes hot quickly.

- Low density so that the pot is light.

Aluminium Body

- Large specific heat capacity so that the handle will not become too hot .

- Poor heat conductor so that heat lost is minimum.

Wooden handle

Application of specific heat capacityCooling system of a car engine

1 2

3

4

Why Sea Breeze occurs during the day?

Specific heat capacity of sand is lower than that of the water.

During the day,Surface of land heats up faster .

Air above the land is hot and rises . Thus creating a region of low pressure.

Cool air above the sea moves towards the land.

1

2

3

4

Why Land Breeze occurs during the night ?

Specific heat capacity of sand is lower than that of the water.

During the night,Surface of land cools down faster.

Air above the sea is still hot and rises . Thus creating a region of low pressure.

Cool air above the land moves towards the sea.

1

2

3

4

Evaluation

1. Material X has a higher specific heat capacity than material Y. Which of the comparison between X and Y is correct ?

A X warms up faster and cools down faster. B X warms up faster but cools down slower. C X warms up slower and cools down slower. D X warms up slower but cools down faster.

Evaluation

2. 200 g of P and 200 g of Q are heated by the same flame for the same period of time. P has a higher rise in temperature. Which of the following statements is correct ?

A Heat capacity of P is higher than that of Q. B Heat capacity of P is lower than that of Q. C More heat is absorbed by P than by Q. D More heat is absorbed by Q than by P.

Evaluation

3. Which of the following is the correct unit for specific heat capacity ?

A J kg-1

B J oC-1

C J kg oC-1

D J kg-1 oC-1

Exercise

Mastery Practice 4.2 pg 115 Q 1, 2, 3,4

Challenge Yourself pg 115 Q 1