Heat Energy

 Heat Energy

Most of us refer the word ‘heat’ to anything that feels warm but scientifically, heat is defined as the flow of energy from a warm to a cooler object. The classification of heat is done on this basis as hot and cold.

Heat energy is all around us, such as in icebergs, volcanoes, and our bodies. Every matter has heat energy.

The result of the movement of minute particles known as atoms, molecules, or ions in liquids, solids, and gases is nothing but heat energy. Heat energy can be transferred from one substance to another, and the flow because of the temperature difference between two objects is known as heat.

Ways Of Transferring Heat Energy

Convection transfers heat energy via air and liquids. The particles move apart and become less dense as the air heats up and hence causing the air to rise. While cooler air moves in from below and heats up.

Radiation warms the air using heat waves that radiate out of the hot object in all directions until absorbed by other objects. Heat transfer by radiation takes place at the speed of light and travels great distances.

Conduction transfers heat from one object to another when they are in direct contact with one another. The travelling molecules of a warm object can increase the energy of the molecules in a cooler object. Solids conduct heat better than gases and liquids since particles are close together.

Particles In Collision

Particles have higher energy at higher temperatures. Some amount of this energy can be transmitted to other particles that are at a lower temperature. For instance, when a fast travelling particle collides with a slower particle in the gas state, it transfers its energy to the other particle and thus increases the speed of slow-moving particles.

When billions of particles collide with each other, a region of high energy transfers across the material until a condition of thermal equilibrium is developed, i.e. the temperature across the material is the same.

Heat Energy Examples

Heat energy is present everywhere, and most people's everyday activities involve heat. A few heat energy examples are stated below.

• The sun radiates electromagnetic waves, travels through outer space, and reaches the Earth's atmosphere. It is responsible for heating the planet and enabling life to thrive.
• The conversion of fuel in cars involves heat energy. The gasoline burns and turns into chemical energy, which then turns into heat. Without heat, it would be impossible for automobiles to function.
• Radiators in cars also use heat energy. The heat produced by cars from burning fuels needs to be released for the engine to perform well. When a specific temperature is reached, water and coolant are released to absorb the heat from the engine. The radiator's surface, the presence of water, and the rotating fan are enough to cool down the engine.
• A steaming cup of cocoa involves heat energy as well. Allowing it to sit at room temperature for a few minutes is enough to lower its temperature, cool enough to drink without burning the tongue.
• Fire from the stove and campfires provide heat energy. Even without direct contact, they can still provide enough heat to cook food and supply warmth to nearby areas.

Heat as a form of energy

 

Because all of the many forms of including heat, can be converted into work, energy, amounts of energy are expressed in units of work, such as joules, foot-pounds, kilowatt-hours, or calories. Exact relationships exist between the amounts of heat added to or removed from a body and the magnitude of the effects on the state of the body. The two units of heat most commonly used are the calorie and the British thermal unit (BTU). The calorie (or gram-calorie) is the amount of energy required to raise the temperature of one gram of water from 14.5 to 15.5 °C; the BTU is the amount of energy required to raise the temperature of one pound of water from 63 to 64 °F. One BTU is approximately 252 calories. Both definitions specify that the temperature changes are to be measured at a constant pressure of one atmosphere, because the amounts of energy involved depend in part on pressure. The calorie used in measuring the energy content of foods is the large calorie, or kilogram-calorie, equal to 1,000 gram-calories.

In general, the amount of energy required to raise a unit mass of a substance through a specified temperature interval is called the heat capacity, or the specific heat, of that substance. The quantity of energy necessary to raise the temperature of a body one degree varies depending upon the restraints imposed. If heat is added to a gas confined at constant volume, the amount of heat needed to cause a one-degree temperature rise is less than if the heat is added to the same gas free to expand (as in a cylinder fitted with a movable piston) and so do work. In the first case, all the energy goes into raising the temperature of the gas, but in the second case, the energy not only contributes to the temperature increase of the gas but also provides the energy necessary for the work done by the gas on the piston. Consequently, the specific heat of a substance depends on these conditions. The most commonly determined specific heats are the specific heat at constant volume and the specific heat at constant pressure. The heat capacities of many solid elements were shown to be closely related to their atomic weights by the French scientists Pierre-Louis Dulong and Alexis-Thérèse Petit in 1819. The so-called law of Dulong and Petit was useful in determining the atomic weights of certain metallic elements, but there are many exceptions to it; the deviations were later found to be explainable on the basis of quantum mechanics.

It is incorrect to speak of the heat in a body, because heat is restricted to energy being transferred. Energy stored in a body is not heat (nor is it work, as work is also energy in transit). It is customary, however, to speak of sensible and latent heat. The latent heat, also called the heat of vaporization, is the amount of energy necessary to change a liquid to a vapour at constant temperature and pressure. The energy required to melt a solid to a liquid is called the heat of fusion, and the heat of sublimation is the energy necessary to change a solid directly to a vapour, these changes also taking place under conditions of constant temperature and pressure.

SI unit of heat is Joules.

Types of Heat Energy Transfer

As mentioned above, heat transfer occurs as long as there is a temperature difference. Heating pavements, boiling water, and feeling the warmth from the sun are all manifestations of energy transfer. There are three types of heat transfer, namely, conduction, convection, and radiation.

Thermal Energy

Thermal energy is a kind of energy and it is generated when the temperature rises. Thermal energy is directly proportional to the change in temperature of the object. Heat is the form of thermal energy. The hotter the substance, the more will be its thermal energy. The rise of thermal energy by increasing the temperature is due to the faster movements of atom and molecules of the substance.

Sometimes the temperature is so high that the molecules of the substance break the bonds from it and leave it. Surprisingly, the states of matter are also dependent on thermal energy. Change in the thermal energy changes the states of matter. Increase in the thermal energy allows the material to change from solid to liquid and then liquid to gas. This is due to the increase in the internal energy of the molecules and atoms.

Types of Thermal Energy

All matters are made from tiny particles called molecules and atoms. They are always in motion and move here and there or vibrating back and forth even at constant temperature and the total sum of all their kinetic energies in all directions is zero. An increase in the temperature raises the kinetic energy of the molecules which tend to change the state of matter. The thermal energy of the matter is increased by three methods, namely, conduction, convection and radiation. These transfer methods of thermal energy are discussed below in details:

Conduction:

Thermal energy transfer is made easy in case of conduction as in this case, energy moves from one molecule to another by vibration. Molecules do not move from their places but their speedy back and forth vibrations transfer the energy effectively. Heat, a form of thermal energy, transfers the energy between the bodies if there are no external hindrances present. Even at the thermal equilibrium the molecules and atoms possess kinetic and potential energies in all directions but their net effect is zero. When heat is transferred to them, they vibrate at their places and transfer the extra energy to the neighbouring particles. This way, heat transfers from one place to another. This type of flow of thermal energy generally happens in the solid phase of the matter.

Convection:

When the heat or thermal energy transfer takes place in the liquid state of the matter, it transfers in layers. In the liquids, there is no restriction for the movements of molecules. When the liquid is heated up, the liquid molecules near to the heat source do move to the place where the temperature is low. This way a current is developed within the liquid and when the hot current moves upwards the blank space is filled up by the cold current. This process continues until all the liquid attains the same temperature throughout.

Radiation:

In the gaseous state of matter, the movement of molecules is so random that they can move to any direction. In radiation, energy transfer takes place in the waveform. These waves are electromagnetic waves which transfer the energy from one molecule to another. Thermal transfer of heat through radiation does not require any medium wherein a medium is required in case of conduction and convection methods to transfer heat or energy. They can travel in a vacuum also. Therefore energy transfers easily in case of radiation as compared to conduction and convection.

Difference Between Heat and Temperature

The difference between Heat and Temperature are tabulated below.

Heat	Temperature
It is a form of energy.	It is the thermal state of a physical body.
It can flow from one body to another.	It is a parameter measurement of a body so it does not flow.
Total amount of heat in a body can only be measured during its flow.	Temperature of a body can be measured.
It does not depend on the amount of heat present in the bodies.	Temperature decides whether there will be any heat flow or not.
It is a process between two matters.	It is the fundamental property of a matter.
It is a path function.	It is a state function.