4.2 specific heat capacity
TRANSCRIPT
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4.2 Understanding Specific Heat Capacity
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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
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Which pot of water take a longer time to boil ?
Requires more heat
Requires less heat
Greater heat capacity Smaller heat capacity
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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
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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
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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.
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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
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Formulae
Specific heat capacity,Qcm
Quantity of heat absorbed or lost , Q = mc
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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.
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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
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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
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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
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Application of specific heat capacityCooling system of a car engine
1 2
3
4
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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
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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
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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.
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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.
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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
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Exercise
Mastery Practice 4.2 pg 115 Q 1, 2, 3,4
Challenge Yourself pg 115 Q 1