4.2 UNDERSTANDING SPECIF IC HEAT CAPACITY
Oct 28, 2014
4.2 UNDERSTANDING SPECIFIC HEA
T CAPACITY
LEARNING OUTCOMES
• A student is able to:• Define specific heat capacity • State that c= Q/ mθ• 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
INDUCTION SET
• Water in the swimming pool and in the pail have different HEAT CAPACITIES
• Equal masses and flame• Temperature of one will increase faster than other
• Water and oil have different SPECIFIC HEAT CAPACITIES
Heat capacity (muatan haba)
The amount of heat required to increase its temperature
by 1ºC
INDUCTION SET
Specific Heat Capacity, c (Muatan haba tentu)
The amount of heat that must be supplied to increase the temperature by 1 °C for a mass of 1 kg of the substance
Specific heat capacity, c = Q__
mθ
SI unit: = J kg-1°C-1 or J kg-1K-1
Q = heat absorbed / released (J)
m = mass of the substance (kg)
θ = temperature difference (°C)
What does specific heat of
aluminum 900 J kg-1°C-1 mean?
900 J of heat needs to be
supplied to 1 kg of aluminum to
produce a 1°C temperature
increase
What does specific heat of
water 4 200 J kg-1°C-1 mean?
4 200 J of heat needs to be
supplied to 1 kg of water to
produce a 1 °C temperature
increase
How much heat energy is required to raise the temperature of 1.5 kg of water from 30 C to its boiling point? The specific heat capacity of water is 4200 J kg-1 °C-1
441 000 J
The physical meaning of specific heat capacity, c
• 2 objects of equal mass are heated at equal rates:
Temperature of object (smaller c) will have a faster temperature
• 2 objects of equal mass are left to cool down
Temperature of object (smaller c) will drop faster.
A substance with a small value of c
1. Heats up and cools at a faster rate Metal (iron, steel and copper ) used as pots
and pans Quickly heated
2. Sensitive to temperature changes A thermometer has low c Heat is absorbed and released easily
A substance with a high value of c
1. Heats up and cools at slower rate. Require more heat to raise its temperature Poor conductor of heat – handle of pot 2. Absorb a great amount of heat without a
high increase in temperature. Eg: Water is used as a cooling agent in a car
radiator.
Material has a high c
Material has a low c
It takes a longer time to be heated.
It becomes hot very quickly.
It does not lose heat easily.
It lose heat easily.
A heat insulator. A good heat conductor.
Conversion of energy(a) Electrical energy from heater transformed into heat energy.
Pt = m c θ , P = IV
(b) Potential energy of a falling object transformed into heat energy.
mgh = m c θ
(c) Kinetic energy of a moving object is transformed into heat energy when it is stop due to friction.
½ mv = m c θ
Applications of c
1. Cooking pota) Copper base• Low c - becomes hot quickly • High density- pot is stable and not
topple over easily
b) Wooden handle
• Large c - the handle not too hot
• Poor conductor of heat
c) Alumni body
• Low c
• Low density – lighter
• Do not react with the food
2. The cooling system of a car engine (m/s 114)
• Water has a high c and lower cost. • Useful as a cooling agent. • A water pump circulates the water. • Heat produced by the engine is absorbed by the water that flows along the space in engine walls.
• The hot water flows to the radiator where heat is lost to the cooler air that flows through the cooling fans.
3.
EXERCISES
2. A 700 W electric heater is used to heat 2 kg of water for 10 minutes. Calculate the temperature rise of the water. The specific heat capacity of water is 4200 J kg-1 ° C -1.
50 ° C
6. A bullet traveling at 60 m s hit a sand bag. The temperature of the bullet rises by 4.5 C. Calculate the specific heat capacity of the bullet.
400 J kg-1 ° C -1
7. A copper block weighing 2 kg is dropped from a height of 20 m. What is the rise in temperature of the copper block after it hits the floor. The specific heat capacity of copper is 400 J kg-1 ° C -1.
0.5 ° C
8. 100 g of hot water at 90 ° C is mixed with 200 g of cold water at 30 ° C. Assuming that no heat is lost, calculate the final temperature of the mixture.
50 ° C