calorimetry, calorimeter and their types

1. Heat Capacity
XI FDC CHEMISTRY
CHAPTER 11
SIDRA JAVED

2. Heat Capacity
Amount of heat absorbed by a substance is directly proportional to the
temperature change
q ∝ ΔT
q = Heat Capacity x ΔT
Where heat capacity is constant of proportionality
Heat Capacity =
Heat
ΔT

3. Heat Capacity
The amount of Heat required to raise the temperature of given amount of
substance by 1 kelvin is called heat capacity.
It is expressed in Joules per Kelvin
Heat Capacity = ----------(i)
Heat
ΔT

4. Specific Heat Capacity
The amount of heat required to raise the temperature of 1 gram of a
substance by 1 Kelvin is called Specific Heat Capacity
It is expressed in joules per gram per kelvin
Specific Heat Capacity (C) = -----------(ii)
Heat
m x ΔT

5. Molar Heat Capacity
The amount of heat required to raise the temperature of one mole of a
substance by one kelvin is called its molar heat capacity.
SI unit of Molar heat Capacity is J.mol-1K-1
Molar Heat Capacity (C) = ------------(iii)
Heat
Moles x ΔT

6. Molar heat capacity at constant pressure
If the quantity of Heat q is absorbed by n moles of the substance and its
temperature raises from T1 to T2 , its molar heat capacity is given by:
C = =
Since heat absorbed by a substance at constant pressure is equal to ΔH
qp = ΔH
∴ CP = =
Or ΔH = nCPΔT
Where Cp is the Molar Heat Capacity of the substance at constant pressure.
q
n(T2-T1)
q
n(ΔT)
qP
n(ΔT)
ΔH
n(ΔT)

7. Molar heat capacity at constant volume
At constant volume:
qV = ΔH = ΔE
And Cv = =
ΔE = nCV ΔT
Where Cv is the molar heat capacity at constant volume
qV
n(ΔT)
ΔE
n(ΔT)

8. Using specific heat of a substance, the quantity of heat abosrbed or evolved
can be evaluated
C =
q = m C ΔT ------(iv)
Similarly by amount of heat can be calculare using molar heat capacity
C =
q = n C ΔT -------(v)
q
m x ΔT
q
n x ΔT

9. Calorimetry
Caorimetry is the science of
meausring heat of chemical
Reaction by measuring the
temperature change
A device that
measures heat flow
is called Calorimeter

10. Constant pressure Calorimetry
In constant pressure calorimetry pressure of the
system is kept constant
A thermally insulated container with a
thermometer and stirrer is used. Generally a
coffee cup calorimeter is used for this purpose.
q = m C ΔT
Where m = mass of reactants
C = specific heat of reaction mixture
ΔT = Change in temperature

11. Constant volume calorimetry
It is used for accurate determination of the
enthalpy of combustion for food fuel and
other compounds
A bomb calorimeter is used for this purpose.
In a bomb calorimeter chemical reaction
takes place under constant volume
conditions.

12. Estimation of energy available from food
Human being require three major classes of food:
1. Carbohydrates
2. Proteins
3. Fats
Carbohydrates and mainly glucose are the main source of energy.
The energy available in glucose can be measured by determining its heat of
combustion.

13. ● Weigh 1.8 g of glucose and place it in holder cup of bomb
calorimeter and seal it.
● Adjust the pressure of oxygen in the calorimeter to about 25 atm.
● Immerse calorimeter in an insulated water bath fixed with a
motorized stirrer and a thermometer.
● Record the temperature of water T1.
● Ignite the glucose electrically when it will burn energy will flow
from the chemicals to the calorimeter and water.
● Record the temperature of water again T2.

14. T1 = 25oC
T2 = 31.52oC
Mass of glucose = 1.8 g
Molar mass = 180 gmol-1
Heat capacity of calorimeter
= 4.321 KJK-1
Increase in temperature
= ΔT = T2 - T1
ΔT = 31.52 - 25 = 6.52
Heat evolved = ΔT x Total heat capacity of
calorimeter
Heat evolved = 6.52 x 4.321= 28.1729 KJ
No of moles of glucose = 1.8/180 = 0.01
moles
Heat evolved by 0.01 mol glucose =
28.1729KJ
Heat evolved by 1 mol glucose =
28.1729/0.01 = 2817.29 KJmol-1

15. End of Lesson