Chapter 10, Problem 1QC

How do the properties of liquids and solid differ, and what happens when happens when happens substances undergo a change of state?

Interpretation Introduction

Interpretation:

The variation in the properties of solids and liquids is to be determined. The changes that occur when there is an interconversion of the physical state of a substance is to be explained.

Concept Introduction:

Matter exists in three physical states, the solid, the liquid, and the gaseous phase. Different physical state has a different arrangement of particles which influences the properties of the same.

For example, a substance in the solid-state has a regular and tightly packed arrangement of particles, whereas the liquid state has loosely packed particles than solids and the particles can slide over each other. In the gaseous phase, there is a random arrangement of particles and the gaseous particles can move freely.

Explanation of Solution

The difference in the properties of solids and liquids is explained below:

In solids, particles remain in a fixed place but vibrate around a fixed position whereas in liquids particles move past one another due to less attractive forces between molecules than among molecules in solid.

Solids have fixed, rigid shapes whereas liquids do not possess a fixed shape and acquire the shape of the container in which it is poured.

The volume of solids remains almost unaffected by moderate pressure whereas liquids can be compressed slightly.

The space between particles is more in liquids as compared to solids. So, liquids can be compressed slightly.

All substances can exist in any of the three physical states. Under some extreme circumstances, the transition from one physical state to another occurs. The transitions between these states are termed as "changes of state or phase changes".

There are six types of phase changes that can take place and are given below.

Melting: In this phase, the conversion from the solid state to the liquid state takes place.

Freezing: In this phase, the conversion from the liquid state to the solid state takes place.

Evaporation: In this phase, the conversion from liquid to the gaseous phase takes place.

Condensation: In this phase, the conversion of a gaseous substance into liquid takes place.

Sublimation: In this phase, the direct conversion of a solid compound into a gas takes place without the formation of liquid.

Deposition: In this phase, the direct conversion of a gaseous substance into a solid takes place without the formation of liquid.

The changes that occur when there is an interconversion of the physical state of a substance is as follows:

Melting of a solid occurs when there is an increase in the kinetic energy of particles and the absorption of energy.

Freezing of a liquid to solid occurs due to a decrease in the kinetic energy of the particles.

Evaporation or sublimation of substances takes place due to an increase in the kinetic energy of molecules and is an endothermic process.

Condensation and deposition are exothermic processes because of a decrease in the kinetic energy of molecules and the release of energy.

Conclusion

The change in the physical state of a substance is accompanied by a change in the arrangement and the kinetic energy of the molecules.