Action of Heat on Substances: Definition, Effects

Action of Heat on Substances: We must have observed the melting of an ice cube. The ice cubes need not be heated to melt. It starts melting once out of thezer as the room temperature is warmer than the refrigerator. Heat is one of the different forms of energy.

When a substance is heated, the molecules and atoms vibrate faster, causing various changes. Sometimes we get back the original substance, whereas in some cases, new substances are formed. In this article, we will provide detailed information on the Action of Heat on Substances. Continue reading to learn more!

Action of Heat on Subtances: Overview

The distance between atoms increases as atoms vibrate faster. The state of matter of the substance is determined by the velocity and spacing of the particles. An object grows and takes up more space due to enhanced molecular mobility. Heat has a variety of consequences. It can be both chemical and physical.

Important Effects of Action of Heat on Substances

Some of the important effects of heat on an object are :

Raises the Temperature: When heat is applied to a substance, the particles of the substance will move with greater speed. With an increase in speed, the kinetic energy of the constituting particles also increases. This causes an increase in the temperature of the substance. If heat is withdrawn from the substance, its temperature decreases and cools down.

Expansion: When substances are subjected to heat, there is an increase in their lengths, areas, and volumes. Expansion occurs because substances vibrate more strongly than before, break from the intermolecular force of attraction, and move further apart. The expansion of liquids is greater than that of solids, while the expansion of gases is the greatest.

Changes state: When a substance absorbs heat, its particles move apart due to the vibration of the particles. The increase in the intermolecular spaces causes a change in the state to occur. When ice cubes are heated, for example, they turn into water, which then turns into vapour when heated further. As a result, a solid transforms into a liquid, and a liquid transforms into a gas. When heat is removed, the opposite happens.

Brings about Chemical Action: Heat is a form of energy, and it plays a major role in bringing about chemical changes. In certain reactions, heat is required to initiate a chemical reaction, and also heat determines the speed at which reactions occur. For example, cooking food requires heat energy that takes place due to heat.

Thermionic Emission: Electrons are emitted from the surface of metals when they are heated to a specific temperature.

Increase in Pressure: With an increase in temperature, the collision between the particles increases which causes an increase in the pressure.

Effect of Removal of Heat From a Substance

When heat is removed from a substance, it has the opposite impact as when heat is supplied to a substance, as described above. These are some of them:

• Decrease in temperature of the substance: The average kinetic energy of a substance is reduced when heat is removed from it. The substance’s temperature drops due to the decrease in average kinetic energy.

• Contraction of the substance: When heat is removed from a substance, the average kinetic energy of the substance’s particles is reduced, reducing the ability of the substance’s particles to move further apart—the substance contracts as a result of this.

Summary of Action of Heat on Substances

We must have noticed some space being left in railway tracks. It is because, during summertime, more heat causes expansion in tracks. When a substance absorbs a specific amount of heat energy, the substance’s temperature rises. The state of the substance may shift from solid to liquid or liquid to gas. When heated, the material expands. When a substance is cooled, or when heat is removed from it, the molecules lose heat and the temperature drops. This page explains all these effects caused due to heat.

Important Questions on Action of Heat on Substances

FAQs on Action of Heat on Substances

Q.1. What are the five effects of heat?
Ans: The following are some of the most important effects of heat on an object:
1. The temperature is raised.
2. Increases the amount of space available.
3. Changes the state of things.
4. Causes a chemical reaction.
5. Physical characteristics are altered.

Q.2. Why do we need heat?
Ans: Heat is used to warm objects, boil water, fry eggs, and melt metal to construct automobiles. Heat is used to generate electricity in a thermal power plant for our daily lives. The term “temperature” refers to the measurement of how hot or cold something is. The temperature is expressed in degrees Celsius \(\left( {{}^ \circ {\text{C}}} \right).\)

Q.3. Why is heat important in physical and chemical changes?
Ans: When heat is supplied to certain compounds, just physical changes occur; no new material or substances are produced. In some compounds, heat causes chemical changes or chemical reactions, resulting in the production of one or more new substances having properties distinct from the original.

Q.4. What type of reaction produces heat?
Ans: Heat energy is liberated in exothermic reactions. The synthesis of new bonds in the products produces excess heat in the process. The combustion reaction is one of the most visible types of an exothermic reaction.

Q.5. What event is endothermic?
Ans: An endothermic process is one in which the system’s enthalpy \({\text{H}}\) (or internal energy \({\text{U}}\)) increases. Such a process absorbs thermal energy from its surroundings, which involves heat transfer into the system.

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