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Thermal EquilibriumThermal Energy ad Heat

1. Thermal energy is a measure of the sum of

kinetic and potential energy in all the

molecules or atoms in an object.2. Heat is the flow of thermal energy.

Temperature

1. Temperature is a measure of the average

kinetic energy which each molecule of an

object possesses.

2. One object is at a higher temperature than

another if the average kinetic energy of each

of its molecules is greater.

Differences between Thermal Energy and Temperature

Thermal Energy Temperature

A form of Energy Degree of hotness of an object.

Unit: Joule (J) Unit: Kelvin (K)/ Degree Celsius (oC)

Sum of the kinetic energy and potential

energy of the particles.

Average kinetic energy of the particles.

Derived quantity Base quantity

Thermal Equilibrium

1. Two objects are in thermal contact when heat

energy can be transferred between them.

2. Thermal equilibrium can be summarized as:

There is no net flow of heat between

two objects that are in thermal

equilibrium. Two objects in thermal

equilibrium have the same

temperature.

Before After

The rate of heat transfer is higher from higher

temperature to lower temperature. Therefore,

there is a net heat flow from object with higher

temperature to object with lower temperature.

Thermal Equilibrium Achieved

- Net Heat Flow = 0.

- Temperature become the same

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Applications of Thermo Equilibrium

Oven

Refrigerator

Thermometer

Calibrating a ThermometerUsually, we take the steam point of pure water as 100oC and the ice point of water as 0oC. After determining

the position of the ice point and steam point, the temperature of an object can be determined by using the

formula

Ice point: Temperature of melting ice. Itis taken to be 0oC.

Steam Point: Temperature of boilingwater. It is taken to be 100oC.

Absolute zero and the Kelvin temperature scale

1. Absolute temperature is the temperature measured in Kelvin scale, which it is a temperature reading made relative to

absolute zero.

2. We can convert a temperature in °C to absolute temperature by adding 273 to the temperature.

For example:

25°C = 273 + 25 = 298 K

100°C = 273 + 100 = 373 K3. Absolute zero is the temperature where thermal energy is at minimum. It is 0 on the Kelvin scale and -273 on the

Celsius scale.

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Specific Heat Capacity

Heat Capacity

Heat capacity is the amount of heat

required to change the temperatureof an object by 1°C.

Specific heat capacity

Specific heat capacity is the

amount of heat required to change

the temperature of 1 kg of a

substance by 1°C.

Amount of heat change,

Q = mc

Gravitational Energy

Thermal Energy

Kinetic Energy Thermal

Energy

Electrical Energy Thermal

Energy

Mixing 2 Liquids

Applications of Specific Heat Capacity

1. Car engine

2. Thermal Radiator

3. Household Apparatus and Utensil4. Sea Breeze

5. Land Breeze

Note:

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Evaporation

There are several ways of making a liquid

evaporate faster:

a) Increase its temperature

b) Increase its surface area

c) Pass air through it or across its surface

d) Make the liquid into a fine spray

A spray is made up of millions of tiny

liquid droplets with a very large total

surface area. The highly curved surfaces

make it easier for molecules to escape.

Cooling by evaporation

1. Blowing air into a liquid will cause the liquid

evaporate faster.

2. During evaporation, latent heat is absorbed

from the liquid (as a surrounding) causing the

temperature of the liquid decreases.

Note

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Gas Laws

Boyle's law

Boyle's law states that the pressure of a gas with

constant mass is inversely proportional to its

volume provided the temperature of the gas iskept constant.

Formula:

Explanation

1. When the volume of gas decreases, the

number of gas particles per unit volumeincreases.

2. As a result, the frequency of collision between

the air particles and the wall of the container

increases.

3. As such, the pressure of the gas increases.

Pressure Law

Pressure law states that for a fixed mass of gas, the

pressure of the gas is directly proportional to the

absolute temperature of the gas provided thevolume of the gas is kept constant.

Formula:

Explanation

1. The kinetic energy of gas molecules increases

with temperature.2. The air molecules collide with the wall of the

container at higher velocity and frequency.

3. The pressure in the gas increases, causing an

increase in volume.

Charles’ Law

Charles’ law states that for a fixed mass of gas, the

volume of the gas is directly proportional to the

absolute temperature of the gas provided the

pressure of the gas is kept constant.

Formula:

Explanation

1. When temperature increases, the average

kinetic energy of the gas particles will increase.

2. The air molecule move faster and collide with

the wall of the container more vigorously at

higher frequency.

3. As a result, the space between the gas particles

increases and the volume of the gas increases.

Universal Gas LawWhen we combine the formula of the 3 gas law, we can deduce the following equation. We call it the

formula of universal gas law.

For a fixed mass of gas,

, or

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