Maarg Manthan · Topic 6.2

States of Matter

Science & Technology › Chemistry – Basic Concepts and Atomic Structure · Topic 6.2

Matter exists in different states depending on temperature and pressure. The three familiar states are solid, which has a fixed shape and volume, liquid, which has a fixed volume but takes the shape of its container, and gas, which has neither a fixed shape nor a fixed volume. In the kinetic theory, matter is made of particles in constant motion, with strong forces in solids, weaker forces in liquids and almost none in gases. Plasma, a hot ionised gas, is the fourth state and the most common in the visible universe, as in stars. The Bose-Einstein condensate is a fifth state formed near absolute zero, first made in 1995 by Eric Cornell and Carl Wieman, and Wolfgang Ketterle, who shared the Nobel Prize in 2001. States change by heating or cooling.

5 min read · UPSC Prelims · Science & Technology · Chemistry – Basic Concepts and Atomic Structure

At a Glance

Common states Solid, liquid, gas
Fourth state Plasma
Fifth state Bose-Einstein condensate
Sublimation Solid to gas directly
Dry ice Solid carbon dioxide
Exam link UPSC Prelims, Science & Technology: Chemistry – Basic Concepts and Atomic Structure

Where Does It Fit?

This is the second topic of the macro on chemistry. After the topic on elements and compounds, it explains the physical forms that matter takes. Previous topic: Elements, Compounds and Molecules. Next topic: Structure of Atoms.

What Are the Properties of Each State?

State	Features and examples
Solid	Particles packed closely in fixed positions, vibrating. Fixed shape and volume, almost incompressible. Ice, iron, wood
Liquid	Particles close but able to slide. Fixed volume, no fixed shape, flows. Water, milk, mercury
Gas	Particles far apart and moving fast. No fixed shape or volume, compressible. Oxygen, nitrogen, LPG
Plasma	A gas heated so much that atoms lose electrons, forming ions and free electrons. Conducts electricity and responds to magnetic fields. Found in the Sun and stars, lightning, neon signs and fluorescent tubes
Bose-Einstein condensate	Atoms cooled to a tiny fraction above absolute zero, about minus 273.15 degrees Celsius, behave as a single quantum entity. Predicted by Satyendra Nath Bose and Albert Einstein
Liquid crystals	A state between solid and liquid, used in displays of watches, phones and televisions

How Does Matter Change State?

Melting and freezing: solid to liquid and back at the melting point, which is 0 degrees Celsius for ice.
Vaporisation: liquid to gas. Evaporation happens at the surface at any temperature, while boiling occurs throughout the liquid at the boiling point, which is 100 degrees Celsius for water at normal pressure.
Condensation: gas to liquid, as dew on grass.
Sublimation: solid to gas without becoming liquid, as in camphor, naphthalene, iodine and dry ice, which is solid carbon dioxide at about minus 78 degrees Celsius. The reverse is deposition.
Latent heat: heat absorbed or released during a change of state without a change in temperature. Steam at 100 degrees Celsius causes worse burns than boiling water because it carries latent heat.
Effect of pressure: raising the pressure raises the boiling point, which is how a pressure cooker works, and lowering it, as on mountains, lowers the boiling point.

What Else Should You Remember?

Gas laws: Boyle’s law says that at constant temperature the pressure of a gas is inversely proportional to its volume. Charles’s law says that at constant pressure the volume is proportional to the absolute temperature. Avogadro’s law relates equal volumes of gases to equal numbers of molecules, as in Elements, Compounds and Molecules.
Absolute zero: the lowest possible temperature, zero kelvin or minus 273.15 degrees Celsius.
Compressed fuels: LPG is liquefied petroleum gas stored under pressure, and CNG is compressed natural gas, which is used in vehicles.
Supercritical fluids: above the critical temperature and pressure, a fluid has properties of both liquid and gas, and supercritical carbon dioxide is used to decaffeinate coffee.
Superfluids: helium cooled near absolute zero flows without friction.
Plasma uses: in plasma cutting, fusion research such as ITER, in which India takes part, and in sterilisation, as in Nuclear Technology and Energy.
Humidity and evaporation: evaporation is faster in warm, dry and windy conditions, and cools the surface, which is why sweat cools the body.
Diffusion: gases mix by diffusion, faster than liquids, as in Characteristics of Solutions.
Kinetic theory: the kinetic theory says that particles of matter are always moving, and temperature is a measure of their average kinetic energy.

Why Does It Matter for the Exam?

Concept questions: properties of each state and examples such as plasma in stars.
Change questions: sublimation examples, latent heat and effect of pressure.
Link to science news: fusion experiments, quantum computing devices that need ultra-cold temperatures and plasma technologies.
Indian link: Satyendra Nath Bose, whose work on statistics of photons gave bosons their name and led to the condensate.
Common errors: mixing evaporation and boiling, or saying that dry ice is frozen water.

As an analytical point, state of matter is a matter of energy and particle motion. Most of the visible universe is plasma, and extreme cold gives states that reveal quantum behaviour.

Why Is This Topic Important?

Facts States and examples asked
Change Sublimation, latent heat
Link Bose and fusion

What Came Next?

The next topic covers the structure of atoms. Next topic: Structure of Atoms.

Key People and Terms

Plasma Ionised gas
Sublimation Solid to gas directly
Latent heat Heat hidden in change of state
Absolute zero Minus 273.15 degrees Celsius
Boyle’s law Pressure inverse to volume
Condensate Atoms in one quantum state

Exam Corner

Points to Remember

Plasma is the most common state in the universe.
BEC named after Bose and Einstein.
Dry ice sublimates.
Boiling point at 1 atm: 100 degrees Celsius for water.
Absolute zero: minus 273.15 degrees Celsius.

Do Not Confuse With

Evaporation and boiling Surface at any temperature versus whole liquid at boiling point
Plasma and gas Ionised versus neutral
Melting and sublimation Solid to liquid versus solid to gas

Memory Hook

Solid, liquid, gas, then plasma bright; BEC near the zero, Bose and Einstein’s right; dry ice sublimates, pressure cooker holds tight.

Mains Angle

Questions link states of matter with modern science. These points add depth.

States Four and five
Change Heat and pressure
Use Plasma and cold

A Question You May Face

An original practice question, not a past paper question.

“Describe the five states of matter and explain the processes by which matter changes from one state to another.”

How to Answer

States Properties.
Plasma Universe.
Change Latent heat.
Laws Gas laws.

GS Relevance

Prelims: states and examples, changes of state, plasma and BEC, gas laws, uses. GS Paper 3: science and technology.

Frequently Asked Questions

What are the states of matter?

The common states are solid, liquid and gas, distinguished by shape, volume and the arrangement and motion of particles. The fourth state is plasma, an ionised gas found in stars, and the fifth is the Bose-Einstein condensate, formed when atoms are cooled to near absolute zero and behave as a single quantum unit.

What is plasma?

Plasma is a state of matter formed when a gas is heated or energised so much that atoms lose electrons, giving a mixture of ions and free electrons. It conducts electricity, responds to magnetic fields, and makes up the Sun and stars, lightning, neon signs and fusion experiments.

What is sublimation?

Sublimation is the change of a solid directly into a gas without passing through the liquid state, as with camphor, naphthalene, iodine and dry ice, which is solid carbon dioxide. The reverse process, in which a gas turns directly into a solid, is called deposition, as in frost.

What is latent heat?

Latent heat is the heat that is absorbed or released when a substance changes state without any change in temperature. It is used to break or form the forces between particles, which is why steam at 100 degrees Celsius carries more heat and causes worse burns than boiling water at the same temperature.

What does Boyle's law say?

Boyle's law states that at constant temperature the pressure of a fixed mass of gas is inversely proportional to its volume. If the volume is halved, the pressure doubles, and the law helps to explain the working of syringes, breathing and compressed gas cylinders.

PYQ Practice — Statement Analysis

1 Plasma is the most common state of visible matter in the universe.

True

As in stars.

2 Dry ice is frozen water.

False

It is solid carbon dioxide.

3 Evaporation occurs only at the boiling point.