NCERT Solutions for Class 9 Science Chapter 1
Matter in Our Surroundings
NCERT Books for Session 2022-2023
CBSE Board and UP Board
Intext Questions
Page No-9
Questions No-3
For any substance, why does the temperature remain constant during the change of state?
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During a change of state, the temperature remains constant. This is because all the heat supplied to increase the temperature is utilised (as latent heat) in changing the state by overcoming the forces of attraction between the particles. Therefore, this heat does not contribute in increasing the temperature of the substance.
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During the change of state of any matter heat is supplied to the substance. The molecules of this matter use heat to overcome the force of attraction between the particles, at this period of time, temperature remains constant. This extra heat is acquired by the molecules in the form of hidden heat called latent heat to change from one state of matter to the other state.
The phenomenon of a steady temperature in the course of a change of state is known as a phase transition. At this point, the delivered heat power is utilized in breaking or forming intermolecular forces in preference to increasing the kinetic power (which determines temperature).
For instance:
1. Melting: When a strong substance melts into a liquid, strength is absorbed to break the sturdy intermolecular forces holding the strong together. This strength is utilized in converting the state of the substance instead of growing the common kinetic strength of the debris.
2. Boiling: Similarly, when a liquid transitions to a gas (boiling), power is absorbed to conquer the intermolecular forces in the liquid, permitting the liquid to exchange into a gaseous state. Again, this power goes into the phase change in preference to raising the temperature.
Conversely:
3. Freezing: During freezing, a liquid transforms right into a stable, and electricity is released because the molecules form ordered structures. This energy is launched with out converting the temperature till the complete substance has undergone the phase trade.
4. Condensation: When a gasoline condenses right into a liquid, energy is released because the fuel debris come collectively and shape a liquid. This released energy doesn’t have an effect on the temperature till the complete segment transition is whole.
This absorption or release of energy without a change in temperature is referred to as “latent heat.” The term “latent” indicates that this heat energy is hidden or stored within the substance during the phase change, not contributing to a change in temperature but rather to a change in the state of matter.