Changing States of Matter

In your daily activities, you will notice if ice is heated it changes into the water if water is heated it changes into steam if steam is cooled it changes into the water if water is cooled it changes into ice. This is a daily life example where we all see the application of the change in the state of the matter, but do you ever think that How is it possible? How this transformation takes place? And on what it all depends? Don’t worry you will get answers to all your questions in this article.

Change of State of Matter

Solid-state, liquid state, and gaseous state are three states of matter, and any physical change in their state is called a change of state of matter. These changes are reversible in nature means they can attain any state again and again. This reversible property of the three states depends upon different parameters and conditions which will be discussed below.

A physical change in a matter is referred to as a change of state of matter. They are reversible modifications that do not require any changes in the matter’s chemical composition. Melting, freezing, sublimation, deposition, condensation, and vaporisation are examples of common state transitions.

We can understand the meaning of a change of states of matter in one more way i.e. when a solid is heated it changes into liquid, and when a liquid is heated it changes into a gas, and when a gas is cooled it changes to a liquid when a liquid is cooled it changes to solid. And, we can interchange these states by:

1. Changing the temperature
2. Changing the pressure

Why do States of Matter Change?

The change in state occurs due to the following factors:

• The change in intermolecular space and force of attraction,
• The change in temperature,
• The change in pressure and
• The change in kinetic energy of the particle.

Let’s discuss each point in more depth as

1. By Changing the Temperature: The temperature effect on heating a matter depends upon the nature of the matter and the conditions required in bringing the change. So, let’s discuss all the 6 interchanges between these states now.

• Solid to Liquid change- This process is known as Melting. The process in which a solid substance changes into a liquid on heating is called melting. On increasing the temperature of the solid the kinetic energy of the particle increase which overcomes the force of attraction between the particles thereby solid melts and is converted into liquid.
• Liquid to Gas change- This process is known as Boiling or Vapourisation. The process in which a liquid changes into gas rapidly on heating is called boiling. The temperature at which a liquid boils and changes rapidly into the gas at atmospheric pressure is called the boiling point of the liquid.
• Gas to Liquid change- This process is known as Condensation. The process of changing gas into liquid by cooling is called condensation. Condensation is the reverse of boiling.
• Liquid to Solid change- This process is known as Freezing. The process of transformation of liquid into a solid by cooling is called freezing. Freezing means solidification. It is the reverse of the melting process.
• Solid to Gas change- This process is known as Sublimation. The change of solid directly into vapor on heating without passing through the intervening liquid state is called sublimation. The common substances which undergo sublimation are ammonium chloride, iodine, camphor, naphthalene, and anthracene. e.g. Solid carbon dioxide(or dry ice) sublimes to form carbon dioxide gas. Naphthalene balls disappear with time without leaving behind any residue.
• Gas to Solid change- This process is known as Deposition or Desublimation. It is a thermodynamic process in which gas changes into a solid directly without entering into the liquid phase.

2. By Changing the Pressure: The physical state of matter can also be changed by changing the pressure. By applying high pressure the particles of a gas can be brought close together means gases can be liquefied easily by applying pressure and reducing temperature. When pressure is applied particles come together thus the force of attraction increases and intermolecular space decreases. Hence, gas liquefies. When pressure around the solid carbon dioxide is reduced its temperature increases and it directly changes into carbon dioxide gas.

Interconversion of Three States of Matter

The states of matter are interconvertible. The state of matter can be changed by changing the temperature or pressure. The transition of one state to another is referred to as the interconversion of matter. It is a process in which matter transitions from one state to another and then returns to its original state with no change in its chemical makeup. Heating may transform solids into liquids. These changes are shown in the figure given below.

Interconversion of Three States of Matter

Important Definition related to Change of State of Matter

• Melting Point: The temperature at which a solid melts to form a liquid at atmospheric pressure is called its melting point. During melting the temperature of ice does not rise even though heat is being supplied continuously due to latent heat of fusion this latent heat is used to overcome the force of attraction between the particles of ice.
• Boiling point: The temperature at which a liquid boils to form vapors at atmospheric pressure is called its boiling point. The boiling point of water is 373 k.
• Latent Heat: The heat energy which has to be supplied to change the state of a substance is called latent heat. It is called latent heat because it becomes/gets hidden in the substance changing state and does not show its presence by raising the temperature. The latent heat which we supply is used up in overcoming the forces of attraction between the particles of a substance during the change of state. Latent heat is of two types: The latent heat of fusion and the latent heat of vaporization.
  • Latent Heat of Fusion (solid to liquid change): The latent heat of fusion( or melting )of a solid to liquid is the quantity of heat in joules required to convert 1 kilogram of the solid (at its melting point) to liquid without any temperature change.
  • Latent Heat of Vaporization (liquid to gas change): During boiling, the temperature of the water does not right even do heat is being supplied continuously as this heat of vaporization is used to overcome the force of attraction between water particles.
• Freezing point: Freezing is the transformation of liquid water into solid ice. The freezing point is the temperature at which it happens.
• Boiling point: The process through which a liquid boils and transforms into a gas is known as vaporization. The boiling point of a liquid is the temperature at which it begins to boil.
• Condensation: The mirror is prone to fog up when you take a hot shower in a closed bathroom. You may be wondering why this occurs. When hot water evaporates from the shower, it cools and loses energy when it comes into touch with colder surfaces such as the mirror. Cooler water particles lack the energy to overcome the forces of attraction between them. They combine to create droplets of liquid water. Condensation is the process through which gas transforms into a liquid.
• Vaporization: If the water is sufficiently heated, it begins to boil. Water vapor bubbles develop in the boiling water. This occurs when liquid water particles gather enough energy to totally overcome the force of attraction between them and transition to the gaseous form. The bubbles rise through the water and exit as steam from the saucepan. The process through which a liquid boils and transforms into a gas is known as vaporization. The boiling point of a liquid is the temperature at which it begins to boil.
• Sublimation: Sublimation is the process through which solids immediately transform into gases. When solids absorb enough energy to totally overcome the forces of attraction between them, this happens. Dry ice is an example of solids that undergo sublimation.
• Evaporation: The change of a liquid into vapor at any temperature below its boiling point is called evaporation. It is a surface phenomenon in which particles from the surface gain enough energy to overcome the forces of attraction. This operation causes cooling because when a liquid evaporates the particles of the liquid absorb heat from the surroundings and its surrounding become cool. Particles on the surface of a liquid have higher kinetic energy than others, so they break the forces of attraction between the particle and escape from the surface of the liquid in the form of vapors.

Sample Problems

Problem 1: Why do we wear cotton clothes in summer?

Solution:

We should wear cotton clothes in summer to stay cool and comfortable, as cotton is good absorber of water, so it absorbs the sweat from the body and exposes it to air for evaporation of sweat. Thus, cools our body. 

Problem 2: Why solid CO₂ is known as dry ice?

Solution:

Solid CO₂ get converted directly to gaseous state on decrease of pressure to 1 atm without coming into liquid state that’s why it is also known as Dry ice. Also, because of this it is placed or stored under high pressure.

Problem 3: Why does evaporation always cause cooling?

Solution:

 The cooling caused by evaporation is based on the fact that when liquid evaporates it takes latent heat of vaporization from surrounding, which on losing heat get cooled. 

Problem 4: Why do we feel cool when we apply acetone to our palms?

Solution:

When we put Acetone on our hand, it gets vaporated by taking heat from our hand and our hand feels cool.

Problem 5: Why gases can be compressed easily but not liquids?

Solution:

This is because particles of gas have huge intermolecular space between them thus have tendency to compress but liquids have already less intermolecular space therefore can’t be compress more.

Problem 6: How humidity affects the process of evaporation?

Solution:

When humidity of the air is low, evaporation rate is increased. Thus more humidity denotes less evaporation.