The energy of a system is its capacity to do work. When work is done on an isolated system the ability of the system to do work (energy) is increased. On the other hand when the system does work its energy decreases.

When the energy is transferred from one body to another due to a temperature difference, it is called heat. When a heater is immersed in a beaker of water, the capacity of the system to do work keeps increasing because hot water has more energy so it can perform more work than the same amount of cold water.

Thermal energy is a form of energy stored in a system as kinetic energy. It is due to the motion of particles in a system. It is a basic form of energy. The transfer of this thermal energy is called heat.

Outline

## Thermal energy vs Heat

 Thermal energy Heat Thermal energy is a measure of energy transfer between two bodies Heat is a transfer of thermal energy between two bodies due to temperature difference It is due to the movement of particles in a system It is the degree of hotness or coldness of a system It increases as the temperature of a system increases due to an increase in the movement of particles It always flows from the hot body towards the cooler one until both have the same temperature It remains in a system as a part of kinetic energy It is the transfer of thermal energy Sources of thermal energy are geothermal energy, solar energy, and energy due to rubbing of hands, etc Natural sources of heat are coal, gas, and oil It has the same units as heat Units of heat are BTU (British thermal unit) calories and joules

## Heat

Heat is a transfer of energy from hot to cold bodies. It is an energy, in transit. When two bodies having different temperatures are put together the energy is transferred from the body having high temperature to the body having low temperature.

Heat cannot be observed physically until we touch it.

### Examples of Heat transfer

• Put the hot cup of coffee in an open place. After some time it gets cold because the energy is transferred from hot coffee to the colder surroundings.
• Put a piece of bread on the toaster and turn it on. The heat is transferred from the toaster to bread.
• The heater in a home provides heat energy to warm the house during winter.
• Put a piece of ice in the water. The ice melts after some time because the heat energy is transferred from water to the ice.
• When we place food in ovens, it becomes hot and cooks because of the transfer of energy from the oven radiation into the food.
• Automobiles fuels such as gasoline are a source of heat energy.

### Sources of heat energy

The main and the biggest source of heat in our solar system is the sun. Some of the other sources are:

• Combustion
• Electric resistance
• Fossil fuels
• Biomass
• Coal
• Gas
• Oil
• Gas boilers
• Combined heat and power plants, etc.

## Thermal energy

Thermal energy is a part of internal energy and is stored in a system as kinetic energy. Like kinetic energy, it is due to the movements of particles within a system.

Thermal energy is the measure of how much energy is transferred between two bodies.

Thermal energy has a direct relationship to temperature. When temperature increases, the movement of particles increases, and thermal energy increases.

It is not energy being transferred rather it remains the part of the internal energy of the system.

### Examples of Thermal energy

• Geothermal energy

It is the energy from the sun. It is generated within the earth’s crust due to radioactive elements present inside.

• A cup of hot chocolate

A cup of hot chocolate contains high thermal energy as compared to the cold one. When the hot chocolate milk cools down, it loses thermal energy to the surrounding environment.

• Fuel cell energy

A fuel cell generates energy from chemical reactions taking place in electro-optical cells. The reaction between two electrodes produces charge particles which are carried by electrolytes. The heat generated in this reaction is used to enhance energy efficiency.

• Heat energy from oceans

Ocean and sea contain large amounts of thermal energy. It is exploited by utilizing temperature differences between shallow and deep water marine areas.

• Melting ice

When a piece of ice is put in water, water has greater thermal energy which is utilized for the melting of ice.

• Hot stove

A hot stove has thermal energy, which is transferred to anything placed on it.

• Energy from animals

Animals such as a cat have heat energy within them. When they sit somewhere like on eggs or a person’s lap, transfer of this energy takes place.

Related Topics

### Sources of thermal energy

The main sources of thermal energy are:

• Solar energy
• Geothermal energy
• Combustion
• Fission
• Fusion
• Microwave
• Plasma
• Oceans
• Biomass, etc.

### Means of Thermal energy transfer (Heat)

There are three ways to transfer heat and thermal energy since they are both analogous.

• By conduction

Conduction is a transfer of heat energy from one body to another by direct contact.

• By convection

Convection is the transfer of heat energy by a fluid such as water or air, etc.

Radiation is the transfer of energy by electromagnetic waves.

## Concepts Berg

What are some examples of thermal energy?

Examples of thermal energy are

• Energy from the sun (solar energy)
• Geothermal energy
• Heat energy from the ocean
• Energy from a heater
• Energy from a hot cup of chocolate, etc.

Is thermal energy the same as heat?

Thermal energy is the energy due to the movement of particles in a system. It always remains in a system as kinetic energy. Whereas heat is a transfer of thermal energy between two bodies due to their temperature differences.

So thermal energy and heat are two different although related terms.

Does more thermal energy mean more heat?

Thermal energy is due to the movements of particles within a system. Since thermal energy is directly related to temperature, an increase in temperature results in increased movement of particles which means that the thermal energy also increases. So more thermal energy does mean more heat.

What are the three types of thermal energy transfers?

There are three types of transfer of thermal energy (heat).

It involves the transfer of energy due to the motion of electromagnetic waves.

• Convection

It involves the transfer of energy due to the motion of hot particles in a fluid.

• Conduction

It involves the transfer of energy by direct contact with molecules.

What is the relationship between heat and thermal energy?

Heat is a transfer of thermal energy between two bodies due to temperature differences and thermal energy measures the kinetic energy of bodies.

Both heat and thermal energy have the same units.

What is the difference between heat and energy?

Heat is the energy that is transferred between two bodies and energy is the ability of the body to do work.

• Energy has a direct relationship to temperature.
• Heat flows due to temperature differences between bodies.

How are heat, internal energy, and thermal energy related to each other?

Internal energy is the energy contained in a system. It is due to the motion of atoms, molecules, or electrons which move, vibrate, and rotate. It is the sum of various types of energies in a system.

Thermal energy is a type of internal energy and remains in a system as kinetic energy.

Heat is a transfer of thermal energy from a body of high temperature to a body of low temperature.

What is the difference between thermodynamics and heat transfer?

Thermodynamics tells us about the feasibility of the reaction or whether the reaction will happen or cease to exist. It tells us why the reactions take place. It does not tell us how long the reaction will occur.

While heat is the rate of thermal energy transfer. It tells us how the reaction takes place. It involves the factor of time which is not present in thermodynamics.

What is the difference between heat and kinetic energy?

Kinetic energy is the energy possessed by a body due to its motion. The motion of particles may be translational, vibrational, or rotational. While heat is a transfer of energy from a hot body to a cooler one.

It means in the case of heat, only the translational part of kinetic energy is transferred.

What is the difference between heat and enthalpy?

Heat is the amount of thermal energy transferred while enthalpy is the total heat content of a system.

In simpler words, we can say that heat transfer changes enthalpy.

Moreover, heat is a path function while enthalpy is a state function.

What is the difference between thermal conductivity and heat capacity?

Thermal conductivity is the ability of a material to conduct heat energy while heat capacity is the ability of a material to absorb heat energy.

OR

Thermal conductivity is the measure of the rate at which the heat can pass through the material while heat capacity is the amount of heat required to raise the temperature of a substance to a certain degree.

What are some fun facts about thermal energy and heat?

Some fun facts about thermal energy are given below;

• Thermal energy and heat are different variables.
• Thermal energy and temperature are different parameters.
• When an ice cube is placed in water, water has greater thermal energy which causes the melting of ice cube.

Which is hotter, infrared or ultraviolet?

Ultraviolet radiation has the greatest energy than visible or infrared radiation. Infrared radiations are the least energetic among these three. As energy corresponds to the temperature or hotness, the order of hotness among UV, visible, and IR is as.

UV > visible > IR (Energy)

What is the difference between heat and electricity?

Electricity is the flow of charges, whereas heat is the transfer of thermal energy between two bodies due to a temperature difference.

Both are forms of energy. Heat can be used to generate electricity and electricity is completely converted into heat. Without heat, there is no electricity. Both occur due to the motion of electrons.

Which one has greater energy, cold water or hot water?

Hot water has greater energy than cold water. As temperature increases energy, the particles of hot water move faster than cold water.

Is thermal energy renewable or non-renewable? What makes it so?

It depends on the source of energy whether the product is renewable or not. Thermal energy from the burning of coal is non-renewable and energy from the sun is renewable.

Similarly, thermal energy from the earth (geothermal energy) is also renewable.

What is thermal inertia?

It is the rate at which an object can gain or lose heat from or to the surrounding. It depends on various factors like density, and thermal conductivity, etc. As a whole, motional inertia in the case of heat transfer is termed thermal inertia.

Does heat travel as fast as sound?

Heat travel depends on various factors like the compactness of the medium molecules, their conductivity, and vibrational patterns. Sound travel depends on similar factors, but sound and heat travel cannot be said to be having the same transfer speed because these various parameters matter a lot.

What is the difference between thermal conductance and thermal conductivity?

Thermal conductivity is the ability of a material to conduct heat. It measures the amount of heat flow per unit time through a unit area with a temperature difference of one degree per unit distance.

Thermal conductance is the facilitation provided to the flow of heat by a material. Thermal conductance is the reciprocal of thermal resistance.