1. THERMAL PROPERTIES OF MATTER

2. Specific heat capacity
INTERNAL ENERGY
The total kinetic energy and potential energy of all atoms or molecules in a material is called internal energy. When the temperature of the material increase the movement of atoms or molecules inside the material increases and the kinetic energy of the atoms increases, so internal energy of the material increases.
Heat capacity
The heat capacity of a substance is amount of heat energy that is needed to raise its temperature by 1°C.
Specific heat capacity
The specific heat capacity of a substance is amount of heat energy that is needed to raise the temperature of 1kg of the substance by 1°C.
The SI unit of specific heat capacity is (J/kg°C).

3. We can use following equation to calculate the specific heat capacity of a substance. Energy required = mass × specific heat capacity × increase in temperature E = mc T Example: A domestic hot water tank contains 200kg of water at 20°C. How much energy must be supplied to heat this water to 70°C? (specific heat capacity of water is 4200 J/kg°C). Ans: E = mc T = 200 × 4200 × (70−20) = J

4. MELTING Melting point BOILING
It is the process that heat is absorbed from the surrounding to change the substance from solid state to liquid state. The temperature of a substance remains constant until all the solid has change to liquid.
Melting point
The temperature at which the solid changes to liquid is called melting point.
BOILING
Boiling is the process that heat absorbed from surrounding to change the substance from liquid state to vapor or gas state. Temperature of the substance remains constant until all the liquid changes to gas.
Boiling point
The temperature at which the liquid changes to gas is called boiling point.

5. FREEZING / SOLIDIFICATION
CONDENSATION
Condensation is the process that substance change from gas state to liquid state by cooling it below boiling point. The temperature of the of the substance remains constant until all the gas changes to liquid.
FREEZING / SOLIDIFICATION
Solidification is the process that substance change from liquid state to solid state by cooling on it. The temperature of the of the substance remains constant until all the liquid changes to solid.

7. HEATING CURVE
When solid is heated for a sufficiently long time, it melts and eventually boils. A heating curve of a solid is shown in the figure below.
Mixture of liquid and gas
Temperature
Mixture of solid and liquid
liquid
solid A B C D E
Time

8. COOLING CURVE
The figure below shows a cooling curve of a gas when energy is flowing out at a constant rate from the gas. The curve can be divided into four regions A
gas
Temperature B C D E
Mixture of liquid and solid
Mixture of gas and liquid
liquid
Time

9. Difference between boiling and evaporation
Boiling take place at definite temperature. (boiling point)
Evaporation take place at any temperature below the boiling point.
Boiling takes place throughout the liquid.
Evaporation take place on the surface of the liquid.
Bubbles are formed in boiling
Bubbles are not formed in evaporation.

10. LATENT HEAT SPECIFIC LATENT HEAT
Energy must be supplied to a substance to melt or to boil it – in other words to make it change state. This energy does not increase the increase substance’s temperature, and for this reason it is known as latent heat (the word ‘latent’ means ‘hidden’). The latent heat is the amount of energy needed to change the state of a substance without changing temperature.
SPECIFIC LATENT HEAT
The specific latent heat is the amount of energy needed to change the state of 1 kg of a substance without changing temperature.
We can use following equation to calculate the specific heat capacity of a substance.
Thermal energy = mass × specific latent heat
E = m × l
The unit latent heat is J/kg

11. SPECIFIC LATENT HEAT OF VAPORIZATION
The specific latent heat of vaporization is amount of heat energy required to change 1kg of a substance from liquid state to gas as its boiling point.
SPECIFIC LATENT HEAT OF FUSION
The specific latent heat of fusion is amount of heat energy required to change 1kg of a substance from solid state to liquid as its melting point.
Example:
In an experiment to find latent heat of fusion of a 15kg metal needs J of heat energy to melt from solid state to liquid. Calculate the latent heat of fusion of metal.
E = m × l
l = E/m = 52000/15 = J/kg

12. THERMAL EXPANSION
Most substances – solid, liquid and gases expand when they are heated. When a substance is heated it makes its molecules vibrate more vigorously. As the vibration become larger, the molecules are pushed further apart and the substance expands in all directions. The reverse happens when the substance is cooled. The vibration become smaller and the substance contracts as its molecules are pulled closer together by force of attraction between them. Gases expands more liquid and liquid expands more than solid.

13. The chart below shows how much one meter length of different materials expands when their temperature goes up by 100°C. For greater lengths and higher temperature increases, the expansion is more.

14. USES OF THERMAL EXPANSION
Liquid - in – glass thermometer make use of the expansion of liquid.
Metal rods can be fitted into metal wheels, by heating wheel. As the wheel cools, it contracts and pulls the rod and wheel tightly together.
A metal lid or cap may stick on a glass jar or a bottle. Heating the lid (for example, by running hot water over it) cause it to expand (the glass expand much less), so the lid loosens and can be removed.
The bimetallic strips used in fire alarms, thermostat and bimetallic thermometers.

15. Fire alarm
When the bimetallic strip in the fire alarm heated up it expands and torches with contact, so current flows through the circuit. As a result bell rings.

16. Bimetal Thermostat
The bimetal thermostat are devices which control temperature. They are fitted to immersion heaters, ovens, and refrigerators and to some room heaters. There are several different designs bimetal type is very common. The diagram below shows thermostat that controls an electric heater. As the rooms warms up, the bimetal strip expands (brass expand more than invar), so two electrical contact separate. This switches of the heater. And when room cools down the bimetal contract and aging torches the contact, so circuit completes and switch on the heater. Temperature can adjust by turning control knob.

17. The bimetal flashing indicator
The indictor bulbs on a car flash on and off because of movements made by tiny bimetal strip. The basic arrangement is shown below. When we turn on the indicator switch, a small electric current passes through the bulb and through the heating coil wound around the bimetal strip. The current is too small to light up the bulb, but it does heat up the bimetal strip. This bend up wards as a result. When the contact touch, the current stops flowing through the heating coil. It takes the easier route straight along the bimetal strip. The bimetal strip now connects bulb directly to the battery, so bulb lights up at full brightness. with no current passing through heating coil, the bimetal strip cools and straightens and contact separate. The current once more has to pass through the heating coil, so the bulb dims as a result. In this way bulb continues on and off.

18. CONSEQUENCES OF THERMAL EXPANSION
The expansion of materials can cause problems. For example metal bridges and railway lines expand on hot days, and there is a danger that they might buckle. To avoid this, bridges in sections, with expansion joints between the sections as shown below. On hot day bridge expands and section between gap decrease. Railway lines are now usually made from metallic alloy that expands very little .

20. Thermal expansion of gases
Gases expand when they are heated, just like solids and liquids. We can understand this by using the kinetic model of matter. The diagram below shows some gas in a cylinder fitted with a piston. At first the gas is cold and its particles press weakly on the piston. When the gas is heated, its particles moves faster. Now they push greater force on the piston and push it upwards. The gas has expanded.

21. The upward force of the gas is balanced by downward force of the piston. So in this situation, the pressure of the gas is remained constant as it has expanded. So for a fixed mass of a gas at constant pressure, the volume gas is directly proportional to the increasing temperature of the gas. This is called Charles’s law. If the piston did not move, the volume of the gas remains constant when it was heated but its pressure would increase.