HEAT AND TEMPERATURE

Heat is defined as energy transferred from a body of higher temperature to a body at lower temperature because of temperature difference. Heat energy is denoted Q.

Temperature is defined as the measure of energy level.

HEAT CAPACITY AND SPECIFIC HEAT CAPACITY

Heat Capacity(C): It is defined as the quantity of energy required to the temperature of a substance through 1K. The S.I. unit of heat capacity is J/K. It can be calculated from the formula below;

Heat Capacity(C)= Heat EnergyTemperature Change= Qθ2-θ1

Where; Q = heat energy

θ2 = Initial temperature

θ1 = Final temperature

Heat capacity can also be calculated from;

Heat Capacity=mass*Specific heat capacity

Specific Heat Capacity (C): Specific heat is defined as the quantity of energy to raise 1kg of a substance through 1K. Specific heat capacity can be calculated from the formula below;

Q=mc(θ2-θ1)

c= Qm(θ2-θ1)

Where m = mass               c = specific heat capacity

θ ₂-θ₁=change in θ=change in temperature

The S.I unit of specific heat capacity is J/kgK or Jkg^-1K^-1.

Example: How much heat energy is required to raise the temperature of 6kg of aluminum from 15K to 35K?

Solution

Q=mc(θ2-θ1)

But m= 6kg; c_al = 900J/kgK; θ1 =15K;   θ2 = 35K

Q = 6kg*900J/kgK*(35K-15K)

Q = 108,000J

MEASUREMENT OF SPECIFIC HEAT CAPACITY

1. An Experiment to Determine the Specific Heat Capacity of a Solid

• Requirements: Thermometer, heater, solid, beam balance, stop watch.
• Diagram:

• Procedure:

Pore two holes on the solid and weigh it using a beam balance to obtain the mass mkg. Drop a liter of oil in the holes to enable good contact. Then insert the thermometer and the heater in the holes. Taking note of the initial temperatureθ1, the heater is switch on for sometime t. The heater is then switched off and the final temperatureθ2 is obtained.

• Calculation:

Assuming that the energy supplied by the heater is equal to energy gained by the solid. Therefore;

Q=Pt=IVt=mc(θ2-θ1)

Therefore; c=Qm(θ2-θ1)= IVtm(θ2-θ1)

Where I = Current ;                                  θ1 = initial temperature;

V = voltage  ;                                              θ2 = final temperature;

t = time taken;                                                       P = power.

1. An Experiment to Measure the Specific Heat Capacity of a Liquid

• Requirements: Thermometer, heater, liquid, stirrer, lagged calorimeter, stop watch.
• Diagram:

• Procedure:

Weigh the liquid in order to obtain the mass mkg. Insert the thermometer and the heater in a liquid of known mass mkg, enough to immerse the heater and the thermometer. Noting the initial temperature θ₁, the heater is switched on for some times t. The heater is switched off and the final temperature  θ2 is noted.

• Calculation:

Assuming heat energy supplied by the heater equal to heat energy gained by the liquid

Q=mc(θ2-θ1)

c=Qm(θ2-θ1)= IVtm(θ2-θ1)= Ptm(θ2-θ1)