8:12:00 PM
Specific
Heat – Activity:
Comparison
of rate of rise in temperature of oil and water:
1. Take 800 C water in
a large jar.
2. Take two test tubes, one filled
with 50 g of water and other with 50 g of oil.
3. Insert two thermometers into
two test tubes, with corks and place them in the hot water jar with clamp of a
retort stand.
4. Observe the changes in the thermometer
readings.
5. Although, the same amount of
heat supplied to water and oil, we observe, the rate of rise in temperature of
the oil is higher than that of the rise in temperature of the water.
6. The rate of rise in
temperature depends on the nature of the substance.
Determine
the components affecting the rate of rise in temperature:
a)
Activity showing the rate of rise in temperature depends upon the mass of the
substance:
1. Take two beakers of equal
volume and take 100 grams of water in one beaker and 200 grams of water in
another beaker.
2. Note down their initial
temperature using thermometers.
3. Heat both beakers till the
temperature of water in the two beakers rises to 600C
4. We need more time to raise the
temperature of 1 Kg of water when compared with 250 grams of water.
5. That means you need to supply
more heat energy to greater quantity of water than lesser quantity of water to
attain same temperature.
6. For same change in temperature
the amount of heat (Q) absorbed by a substance is directly proportional to its
mass (m).
=>
Q α m (when ΔT is constant)
b.
Activity showing the rate of rise in temperature depends upon the amount of
heat (Q) absorbed by the substance:
1. Take 1 liter of water in a
beaker and heat it over a constant flame.
2. Note the temperature changes
(ΔT) for every two minutes.
3. We will notice that the
temperature rise with time in constant proportions.
4. That means, for the same mass
(m) of water the change in temperature is proportional to the amount of heat
(Q) absorbed by the substance.
=>
Q α ΔT.
Derivation
of Equation for specific heat (S):
1. For same change in temperature
the amount of heat (Q) absorbed by a substance is directly proportion to its
mass (m).
=>
Q α m - - - - - - - - - - I
2. For same mass (m) of water the
change in temperature is proportional to the amount of heat (Q) absorbed by it.
=>
Q α ΔT - - - - - - - - - - II
3. From the above I, II
equations, we get
=>
Q α m ΔT
=>
Q = m S ΔT
4. The Constant ‘S’ in the above
equation is called ‘Specific heat’ of the substance.
Specific
Heat
Specific
Heat – Definition:
The specific heat of substance is
the amount of heat required to raise the temperature of unit mass of the
substance by one unit. It is represented by ‘S’.
Specific
Heat
Specific heat units:
C.G.S
system: cal/g 0C
S.I
System: J/Kg.K
1 cal/g 0C = 4.2x103
J/Kg.K
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