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Liquid State of Matter

  • Last Updated : 29 Nov, 2021

Solid, liquid, and gas are the three distinct physical states of matter that matter can adopt in most settings. Other states, such as plasma, Bose-Einstein condensates, and neutron stars, may exist in extreme settings. It’s also thought that other states, such as quark-gluon plasmas, are feasible. Hot plasma, in the form of the rarefied interstellar medium and dense stars, makes up a large portion of the universe’s atomic stuff. 

In the past, states of matter were separated by qualitative distinctions in their bulk qualities. Solid matter maintains a constant volume and shape; liquid matter adapts to the shape of its container but only minimally changes volume, and gas matter expands to fill the volume and shape of its container. Each of the three classical states of matter has the ability to transition into the other two classical states.

Liquid State

Liquids are made up of tiny particles known as molecules. The intermolecular forces of attraction between liquid molecules are relatively strong. The molecules in a liquid are comparatively close to each other as compared to those in a gas. The molecules are constantly moving at random. In a liquid, the average kinetic energy of molecules is proportional to the absolute temperature.

Characteristics of Liquids

  1. Liquids do not Have a Fixed Shape- Liquids have no fixed shape and will take on the shape of any container they are placed in. This is because the interparticle interactions are weak, and particles in one layer can readily slide across particles in another layer. As a result, a liquid will take on the shape of the container it is maintained in.
  2. Liquids Occupy a Definite Volume- Despite the fact that liquids do not have a distinct shape, they do have a volume. A liquid, like a solid, cannot be squeezed by putting pressure on it. The liquids’ interparticle interactions are so strong that no amount of pressure can overcome them.
  3. Liquids have Flexibility and not Rigidity- Liquids have fluidity rather than rigidity, which means they flow. It’s because liquids have fewer intermolecular forces than solids. However, the relative fluidity of different liquids varies. Water, for example, moves more quickly than honey.
  4. Liquids have a Lesser Density- When compared to solids, liquids are often lighter. This is due to the fact that the liquid form of the same substance has a higher number of interparticle gaps than the solid state. Ice (in its solid state) floats on water (liquid state). Both are chemically identical and contain the same molecules, however, ice has a more porous structure than water. As a result, the volume of ice is more than that of water for a given mass, and its density is lower. As a result, ice floats on the surface of the water.
  5. Kinetic Energy of Particles is More than the Solid State- When opposed to the solid-state, the particles in the liquid state are less densely packed. The interparticle forces as a result are weaker. As a result, the particles’ kinetic energy in the liquid state is greater than in the solid state. As the temperature rises, it climbs even more.
  6. Particles in the Liquid State can Easily Diffuse- The particles in a liquid state can disperse more easily than those in a solid state due to lower intermolecular forces of attraction. This feature aids in the mixing of different liquids. Water and alcohol, for example, are both liquids that can easily mix to form a liquid mixture or solution. When the physical conditions of a liquid change, the liquid’s basic nature changes as well.

Properties of Liquids


The process of converting a liquid into its vapours is known as Evaporation.

A liquid’s molecules are in a continual state of motion and have kinetic energy, but not all molecules have the same kinetic energy. Its value might range from very low to very high. As a result, those molecules existing at the liquid’s surface with a greater kinetic energy value will overcome the attraction forces and escape into space above the liquid surface, appearing as vapours. 

Factors Affecting Rate of Evaporation

  • Nature of the liquid-The rate of evaporation is determined by intermolecular attraction forces. The lower the rate of evaporation, the bigger the magnitude of forces.
  • Temperature- The rate of evaporation increases as the temperature rises.
  • Surface area- The rate of evaporation will be faster if the surface area is larger.

Vapour Pressure

The vapour pressure is the pressure exerted by vapours in equilibrium with the liquid at a certain temperature. It arises only as a result of the kinetic phenomenon and is hence unaffected by the amount of liquid present. It is mostly determined by the liquid’s temperature.

Factors Affecting Vapour Pressure

  • Nature of the Liquid- The magnitude of the liquid’s intermolecular forces determines the vapour pressure. When these forces are modest, the molecules easily convert to vapour, resulting in a high equilibrium vapour pressure. If these forces are substantial, however, the molecules will not convert into vapours, and the vapour pressure will be relatively low.
  • The temperature of the Liquid- The vapour pressure of a liquid rises as the average kinetic energy rises with the rise in temperature.

Boiling Point of Liquids

The temperature at which a liquid’s vapour pressure equals the surrounding air pressure is known as the boiling point. As a result, the boiling point is the result of increased vapour pressure rather than the heating process.

Factors Affecting the Boiling Point

  • Pressure- When the external pressure is:
    • The boiling point of the liquid is lower than the standard boiling point when the pressure is less than 1 atm.
    • The boiling point of a liquid is known as the normal boiling point when it is equal to 1 atm.
    • The boiling point of the liquid is higher than its normal boiling point when the pressure is more than 1 atm.
  • Type of Molecules- f the intermolecular forces between the molecules are-
    • Relatively high, the boiling point will likewise be relatively high.
    • Relatively low, the boiling point will be low as well.

Surface Tension of Liquids

The molecules in a liquid are subjected to the same intermolecular force from all sides, but molecules on the liquid’s surface behave differently than those in the interior. Because of the inward pull of the molecules, the molecules on the liquid’s surface experience tension. Surface tension is the term for this phenomenon.

The inward attraction tends to contract the liquid’s surface. As a result, the surface takes on the characteristics of a stretched membrane.

Factors Affecting Surface Tension of Liquids

  • The temperature of the liquid- As the temperature rises, the surface tension falls. This is because when the temperature rises, the kinetic energy rises, resulting in a decrease in intermolecular forces of attraction and, as a result, a drop in surface tension.
  • Nature of the liquid- The surface tension of a liquid is determined by the intermolecular forces of attraction existing in its molecules. The larger the magnitude of force, the higher the surface tension value.


The liquids do not all move at the same rate. Water, alcohol, kerosene, oil, and other liquids flow quickly, while honey, glycerol, castor oil, and other liquids flow slowly. As a result, viscosity can be described as a liquid’s internal resistance to flow.

Different intermolecular forces of attraction exist in different liquids, resulting in internal resistance. When these forces are strong, the liquid becomes more viscous, and when they are weak, the fluid becomes less viscous.

When a liquid flows, the layer of liquid in direct touch with the surface remains motionless; as the distance from the fixed surface increases, the layers’ velocity increases. Laminated flow is a type of flow in which the velocity varies in a regular pattern. The layer immediately below seeks to slow down the velocity, while the layer above accelerates it.

Coefficient of Viscosity

The force required to maintain flow in these three layers is determined by two variables: the area in contact (A) and the velocity gradient du/dx.

The velocity gradient is given by the quantity of du/dx when the velocity of the layer at a distance dx is varied by a value du. To keep the layers flowing, some force is required.

Force (f) ∝ (A)

Force (f) ∝ du/dx

Force (f) ∝ A × du/dx=ηA x du/dx

Hence, η is called the coefficient of viscosity.

The force applied per unit area to maintain a unit relative velocity between the two layers of a liquid at a unit distance can be characterised as the viscosity coefficient.

Factors Influencing Viscosity of Liquids

  1. Temperature- The viscosity of a liquid decreases as the temperature rises.
  2. Nature of liquid- Viscosity is higher in liquids with a stronger intermolecular force of attraction.
  3. Molecular mass- The molecular mass of a substance increases its viscosity.

Sample Questions

Question 1:  What is the liquid state of matter?


The following are some of the features of the liquid state of matter:

  • Liquid particles are less closely packed than solid particles.
  • Solids have a weaker intermolecular force of attraction than gases, whereas gases have a stronger intermolecular force of attraction.
  • They have a constant volume but no constant shape.
  • They are not compressible. To compress the liquids, a lot of pressure is needed.
  • Solids have a lower density than liquids.
  • Liquids do not have a rigidity. They are malleable.

Question 2: What is the boiling point of a liquid?


The boiling point is the temperature at which a liquid’s vapour pressure matches the surrounding air pressure. As a result, rather than the heating process, increased vapour pressure causes the boiling point to rise.

Question 3: What is the difference between boiling and evaporation?


The main distinction between boiling and evaporation is that evaporation occurs on the surface of the liquid, whereas boiling occurs in the bulk of the liquid.

Question 4: What is viscosity?


viscosity is the resistance of a fluid (liquid or gas) to changing shape or moving adjacent sections relative to one another. The term “viscosity” refers to the resistance to flow. Fluidity is defined as the reciprocal of viscosity, which is a measure of flow ease.

Question 5: What are the factors that affect the viscosity of a liquid?


  1. Temperature- As the temperature rises, the viscosity of a liquid reduces.
  2. The nature of the liquid- Liquids with a stronger intermolecular force of attraction have a higher viscosity.
  3. Molecular mass- A substance’s molecular mass affects its viscosity.

Question 6: What is vapour pressure?


At a given temperature, the vapour pressure is the pressure exerted by vapours in equilibrium with the liquid. It is caused only by the kinetic phenomenon and is hence unaffected by the amount of liquid present.

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