11 Heat Capacity and Specific Heat Capacity

HEAT CAPACITY &

SPECIFIC HEAT CAPACITYTOPIC 11: THERMAL PROPERTIES OF MATTER

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WHAT HAPPENS TO MATTER WHEN THERMAL ENERGY IS

APPLIED TO IT?

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OF THE MATTER

THERMAL ENERGY

CAN

Change the temperature

Change the state

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FOCUS ONCHANGING THE TEMPERATURE

OF THE SUBSTANCE

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WHAT DO WE KNOW?When heat is applied to a substance.

The temperature of the substance will increase.

Heat Energy Applied

Change in Temperature of

substance

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HEAT CAPACITYThe amount of heat energy needed to

increase the temperature of a substance by 1 Kelvin or by 1 degrees Celsius.

Heat Capacity

Heat Energy

Change in Temperature

QC =

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“100g of water requires 12 600J of thermal energy to raise it from

300C to 600C”

Calculate its heat capacity.

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“100g of water requires 12 600J of thermal energy to raise it from

300C to 600C”

Calculate the heat capacity for 1000g of water.

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The heavier the mass of the substance, more thermal energy needed to increase

the temperature by 1K, the bigger the heat capacity.

mQC

mQC

HEAT CAPACITY

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How can we compare the heat capacity of different materials more meaningfully ?

How much thermal energy do we need to increase the temperature of these substance ?

aluminium cooper

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EXAMINE THE HEAT CAPACITY PER UNIT MASS

OR SPECIFIC HEAT CAPACITY

OF THE SUBSTANCE

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SPECIFIC HEAT CAPACITYThe amount of thermal energy required to

raise the temperature of 1 kg of a substance by 1 K or 10C

Heat Energy Applied

Change in Temperature by

1 K or 1ºC1 kg

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SPECIFIC HEAT CAPACITYis a property of the material.

The SI unit of specific heat capacity is Jkg-1K-1

Each material has its own unique specific heat capacity.

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Copper

400 J/kgK

Brass

380 J/kgKAluminium

900 J/kgK

SPECIFIC HEAT

CAPACITIES

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Ice2100 J/kgK

Glass 670 J/kgK

Water

4200 J/kgK

SPECIFIC HEAT

CAPACITIES

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WHAT DOES THE VALUE FOR THE SPECIFIC HEAT

CAPACITY MEAN ?

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Copper

400 J/kgK

1 kg of Cooper requires 400J of thermal energy to increase

its temperature by 1K.

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Water

4200 J/kgK

1 kg of water requires 4200J of thermal energy to increase

its temperature by 1K.

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Ice2100 J/kgK

Brass

380 J/kgK

Which of the two substances will be easier to heat up?

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Aluminium

900 J/kgK

Glass 670 J/kgK

Which of the two substances will take longer time to heat up?

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The higher the specific heat capacity, more thermal energy is needed to increase its temperature by 1K.

SPECIFIC HEAT CAPACITY

m

Qc

m

Q c

For different substances of equal masses,

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SPECIFIC HEAT CAPACITYThe amount of thermal energy required to

raise the temperature of 1 kg of a substance by 1 K or 10C

Heat Capacity

Heat Energy

Change in Temperature

Qc =m

Mass

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Thermal Energy = Power X Time Taken

WHAT ARE THE SOURCES OF THERMAL ENERGY?

Bunsen Burner Electric Burner

= P x tQ Heater

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What is the amount of energy required to raise the temperature of 2 kg copper from 300C to 800C, given that the specific heat

capacity of copper is 400 Jkg-1 0C-1 ?

EXAMPLE EXERCISE 1

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EXAMPLE EXERCISE 1

Thermal Energy

MassSpecific Heat

CapacityChange in

Temperature= X X

Q c= mCu Cu Cu CuX X

= 2 kg 400 J/kgºC (80 - 30)ºCX X

=QCu Pre

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An electric kettle contains an immersion heater of power 2.0 kW. It takes 5 minutes to heat

2.0 kg of water from 300C to 1000C.

Assuming no energy is lost to the surrounding, what is the specific heat capacity of water?

EXAMPLE EXERCISE 2

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EXAMPLE EXERCISE 2

=

Thermal Energy supplied to water by heater

=Thermal Energy use to increase

temperature of the water

cmwater X XP X t = water waterheater

Q =heater Q water

= 2kg (100 - 30)ºCX XcX water2000W 300s

cwater

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0.3 kg of water at 100 0C is poured into a copper vessel of mass 0.1 kg at 300C.

What is the final temperature of water assuming there is no energy lost to the

surroundings?

EXAMPLE EXERCISE 3

Specific heat capacity of copper = 400 Jkg-1 0C-1 Specific heat capacity of water = 4200 Jkg-1 0C-1

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EXAMPLE EXERCISE 3

0.3 kg100 0C

0.1 kg300C

water copper

Initial Final

? 0C

water & copper

= 4200 J/kg0Cc water = 400 J/kg0C c Cu

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EXAMPLE EXERCISE 3

Thermal Energy lost by water

=Thermal Energy gained

by copper

Q =water Q copper

=mwater cwater water mCu c Cu Cu

=X X0.3kg 4200J/kg0C (100 - 0C) 0.1kg 400J/kg0C ( 0C- 30)XX

= Pre

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SUMMARIZATION

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QC =

The amount of thermal energy required to

increase the temperature of a substance by

1 K or 10C

“Heat Capacity, C”

Qc =m

The amount of thermal energy required to

increase the temperatureof 1 kg of a substance by

1 K or 10C

“Specific Heat Capacity, c”

J/kg0C J/kgK J/0C J/K

SUMMARIZATION

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Thermal Energy supplied to substance by heater

=Thermal Energy to increase

temperature of the substance

=

=

SUMMARIZATION

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Thermal Energy lost by Substance A

=Thermal Energy gained

by Substance B

=

=

The heavier the mass of the substance, more thermal energy needed to increase

the temperature by 1K, the bigger the heat capacity.

mQC

mQC

HEAT CAPACITY

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The higher the specific heat capacity, more thermal energy is needed to increase its temperature by 1K.

SPECIFIC HEAT CAPACITY

m

Qc

m

Q c

For different substances of equal masses,

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