CHAPTER ELEVEN:���THERMAL PROPERTIES OF MATTER:

�The following points are to be discussed:�Temperature and heat � Measurement of temperature � Ideal-gas equation and absolute temperature �Thermal expansion � Specific heat capacity � Calorimetry � Change of state� Heat transfer� Newton’s law of cooling�

• Heat:
• Heat is that form of energy that flows from one body to another body or it surrounding due to difference in temperature.
• (Note only that energy which flows from one point to another due to difference in temperature is heat.)
• Heat is measured in Joule/Calorie/kilocalorie.

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• Temperature:
• Temperature is measure of degree of hotness or coldness of body.
• (Note: Heat and temperature are related to each other as sugar and sweetness if you add sugar sweetness increases similarly when heat is given in any body temperature increases and when heat is removed temperature decreases.)
• The S.I. Unit of Temperature is Kelvin (K)  and some of the commonly used units are: Fahrenheit (°F) and Celsius (°C)

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Measurement of temperature

To measure temperature the change that takes place due to temperature change is measured.

Any phenomenon in nature which takes place at a particular temperature is taken as reference.

For the definition of any standard scale, two fixed reference points are needed.

The ice point and the steam point of water are two convenient fixed points and are known as the freezing and boiling points. These two points are the temperatures at which pure water freezes and boils under standard pressure.

Natural phenomena in different Scale

This is because the slope of the graph is constant between two scales A and B.

Ideal-gas equation and absolute temperature

An equation which relates pressure P, temperature T and volume V of a gas is called gas equation.

Those gases which follow the gas equation are called ideal gas, but in actual practice the gases behavior varies such gases are called real gas.

The ideal gas equation is represented as-

PV=µRT

Where P= Pressure of the gas

V= Volume of the gas

µ = Number of moles of the gas

R = a constant called gas constant

T = Temperature in Kelvin scale

Here, T = t+273.15 ,t is temperature in Celsius scale.

When we put this in above equation-

PV=µR( t+273.15)

The graph between P &t and P & V is given –

If V=0 or P=0

The t+ 273.15 = 0

Thus t = -273.15⁰C .This temperature is called absolute zero temperature.

Thus the temperature at which pressure or volume of an ideal gas becomes is called absolute zero temperature. This is lower point of Kelvin scale. This temperature is 0K.(Which is equal to -273.15⁰C)

HEAT CAPACITY

Specific heat capacity

CALORIMETRY

The study of measurement of heat is calorimetry.

A device in which heat measurement can be made is called a calorimeter

Principle of calorimetry

When two isolated bodies interact thermally the heat lost by one body is equal to heat gained by another body.

Heat Lost = Heat gained.

CHANGE OF STATE

Change in state is another effect of heat absorbed or heat rejected by a substance.

HEAT TRANSFER

Conduction

 Thermal conductivity

Convection

Comparison

NEWTON’S LAW OF COOLING

According to Newton’s law of cooling “For small temperature difference rate of cooling of a body is directly proportional to difference in temperature of body and its surrounding.