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At the end of the lesson, students should be able:
•Define specific heat capacity
•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
CHAPTER 4.2: SPECIFIC HEAT CAPACITY
CONCEPT OF SPECIFIC HEAT CAPACITY ( c )
SPECIFIC HEAT CAPACITY OF A LIQUID
SPECIFIC HEAT CAPACITY OF A SOLID
APPLICATIONS OF SPECIFIC HEAT CAPACITY
THE SPECIFIC HEAT CAPACITY ( c )
The heat capacity, c, of an object is defined as the amount of heat energy required to raise its temperature by 1oC or 1K.
The unit of heat capacity is JoC-1 or K-1
The heat capacity of an object depends on ;
(i) the mass of the object
(ii) the substances it is made up of
CONCEPT OF HEAT CAPACITY
1 minute 1 minute2 minute3 minute 2 minute3 minute4 minute5 minute
The water in kettle B takes a longer time to boil. This because a greater mass of water requires a greater amount of heat to boil. This shows that the water in kettle B has a greater heat capacity.
Kettle A Kettle B
100oC 100oC
What is the relationship What is the relationship between heat, Q, between heat, Q, temperature, temperature, θθ, and mass, m , and mass, m of a substance?of a substance?
θ
Beaker A
500 g
20 0C - 25 0C
Beaker B
500 g
20 0C - 30 0C
Relationship between heat, Q and temperature, θ
Beaker A600 g of water20 0C – 30 0C
Beaker B300 g of water20 0C – 30 0C
Relationship between heat, Q and mass, θ
Specific heat capacity of a substance is the amount of heat requires to increase the temperature by 1 0C for a mass of 1 kg of the substances
SI Unit for specific heat capacity J kg-1 0C-1
mQ
c
SPECIFIC HEAT CAPACITY FOR SOME MATERIALS
substance Specific heat capacityJ kg-1 0C-1
Air 1000
Aluminium 900
Glass 840
Iron 440
Copper 390
Brass 370
Lead 130
Mercury 140
Water Ice Liquid Steam
210042002000
For example, the specific heat capacity of lead is
130 J kg-1 0C-1
This means that 130 J of heat requires to raise the temperature of 1 kg block of lead through 1 0C
1kg lead1kg lead
1kg lead1kg lead
1kg lead1kg lead
θ1= 16 0C θ2= 17 0C
Amount of heat supplied, Q = 130J
CONVERSION OF ENERGY
Electrical energy
Electrical energy
Kinetic energyKinetic energy
Potential energy
Potential energy
Released by Released by heater with heater with power, Ppower, P
Released by Released by heater with heater with power, Ppower, P
Lost by object Lost by object falling from falling from
high positionhigh position
Lost by object Lost by object falling from falling from
high positionhigh position
Lost when Lost when moving object moving object is stopped by is stopped by
frictionfriction
Lost when Lost when moving object moving object is stopped by is stopped by
frictionfriction
Heat energyHeat
energy
Heat energyHeat
energy
Heat energyHeat
energy
Pt = mcθ
mgh = mcθ
1/2mv2 = mcθ
Power supply
stirrer
Thermometer
Immersion heater
Polystyrene cup
water
TO DETERMINE THE SPECIFIC HEAT CAPACITY OF WATER
The specific heat capacity in the experiment is higher than standard value ( 4 200 J kg-1 oC-1 ). This is because some heat is lost to the surroundings.
The specific heat capacity of water can be determined using the electrical method.
Thermometer
Immersion heater
Aluminium cylinder
Polystyrene sheet
Power supply
The aluminium cylinder is wrapped with a felt cloth to reduce the heat loss to the surroundings and the polystyrene sheet acts as a heat insulator to avoid heat loss to the surface of the table
The specific heat capacity of aluminium can be determined using the electrical method.
TO DETERMINE THE SPECIFIC HEAT CAPACITY OF SOLID ALUMINIUM
APPLICATIONS OF SPECIFIC HEAT CAPACITY
Cooking Utensils
A metal has low specific and its temperature increases easily when heated.
Metals are normally used as pans and heating filaments of kettles so that food and water can be heated faster.
This is because only a little amount of heat is needed to heat the metal. Therefore more heat is transferred to the food.
The handles of pots and pans are usually made of materials of high specific or poor heat conductors.
APPLICATIONS OF SPECIFIC HEAT CAPACITY
Cooling System
Cooling fins
Incoming hot air
Radiator
Heat released
fan
engine
Cylinder engine
Pump
APPLICATIONS OF SPECIFIC HEAT CAPACITY
Cooling System
Water carries the heat out of the engine and releases it to the surroundings.
A fan is used to cool the hot water.
Heat from the engine is transferred to the water
The cold water is then pumped back to the engine block to cool the engine
APPLICATIONS OF SPECIFIC HEAT CAPACITY
The Weather
The existence of ponds, lakes and the sea influence the weather
During the day, water absorbs heat from the surroundings
At night, water releases the heat absorbed to maintain the temperature of the surroundings.
Therefore the area near water does not have a wide temperature range.
PHENOMENA OF SPECIFIC HEAT CAPACITY
Sea Breeze
The land
Hot air
Cool air
during the day, the land and the sea receive the same amount of heat from the sun.
The land is heated to a higher temperature than the sea because water has a higher specific heat capacity than earth.
This causes the air above the land to be hotter than the air above the sea
The hot air above the land flows up and the cool air from the sea flows towards the land.
The movement of air causes wind to blow from the sea, therefore a sea breeze is produced.
The land
Hot air
Cool air
Land Breeze
PHENOMENA OF SPECIFIC HEAT CAPACITY
At night, the air above the land the sea release heat to the atmosphere.
The temperature of the sea decreases more slowly than the temperature of the land because water has a higher specific heat capacity than earth
The land becomes colder than the sea
The hot air above the sea flows upwards and the cool air from the land flows towards the sea
A land breeze is produced due to the movement of air from the land towards the sea
How much energy is required to raise the temperature of a 3 kg sheet of glass from 24 0C to 34 0C?
( Specific heat capacity of glass = 840 J kg-1 0C-1)
m = 3 kg
θ = 34 0C -24 0C = 10 0C
Q = mcθ
Q = (3)(840)(10)
= 25200 J
ACTIVITYACTIVITYsubstance Specific heat capacity, J kg-1 0C-1
air 1000
Iron 440
Lead 130
Liquid water 4200
Discussion :
•Do substances with high specific heat capacities generally heat up quickly?
•Does this make them good heat conductors or poor heat conductors?
ANSWER:
Higher value of specific heat capacity will require longer time to heat up.
So, this will make them as a poor conductor
Lower value of specific heat capacity will heat up quickly.
So, this will make them as a good conductor
At the end of the lesson, students should be able:
•Define specific heat capacity
•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
1. Define specific heat capacity
The amount of heat required to change the temperature of 1 kg of a material by 1 0C.
2. Equation :
3. SI unit:
J kg-1 0C-1
mQ
c
4. Materials that are good heat conductor
have heat capacities.
4. Materials that are poor heat conductor
have heat capacities.
5. Give examples of applications of specific heat capacity
low
high
