Grade 7
  1. Introduction to Chemistry  1.1. What is Chemistry?  1.2. Importance of chemistry in daily life  1.3. Branches of chemistry  1.4. Scientific Method in Chemistry  1.5. Laboratory Safety Rules and Precautions  1.6. Common Laboratory Equipment and Their Uses  1.7. Units of measurement in chemistry
  2. Matter and its properties  2.1. Definition of Matter  2.2. Classification of matter  2.3. Properties of matter  2.3.1. Physical properties  2.3.2. Chemical properties  2.4. States of matter  2.4.1. Solid state  2.4.2. Fluid state  2.4.3. Gaseous state  2.4.4. Plasma and Bose–Einstein condensates  2.5. Changes in the states of matter  2.5.1. Melting and freezing  2.5.2. Evaporation and Condensation  2.5.3. Sublimation and deposition  2.6. Density and its applications  2.7. Diffusion and its importance
  3. Elements, Compounds, and Mixtures  3.1. Definition of the element  3.2. Classification of elements  3.3. Metals, Nonmetals and Metalloids  3.4. Noble gases and their properties  3.5. Introduction to the Periodic Table  3.6. Definition of Compound  3.7. Properties of Compounds  3.8. Introduction to Chemical Formulas  3.9. Definition of Mixture  3.10. Types of mixtures  3.10.1. Homogeneous mixture  3.10.2. Heterogeneous mixtures  3.11. Difference Between Compounds and Mixtures  3.12. Solutions, Colloids and Suspensions
  4. Separation of mixtures  4.1. Need for separation of mixtures  4.2. Separation methods  4.2.1. Filtration  4.2.2. Sedimentation and decantation  4.2.3. Evaporation  4.2.4. Crystallization  4.2.5. Distillation  4.2.6. Chromatography  4.2.7. Magnetic Separation  4.2.8. Centrifugation
  5. Atomic Structure  5.1. Introduction to Atoms  5.2. Structure of the atom  5.2.1. Nucleus and electron cloud  5.3. Subatomic particles  5.3.1. Proton  5.3.2. Neutron  5.3.3. Electrons  5.4. Atomic number and mass number  5.5. Isotopes and their uses  5.6. Ions and ion formation
  6. Periodic table  6.1. Introduction to the Periodic Table  6.2. Groups and periods  6.3. Trends in the Periodic Table  6.3.1. Atomic Size  6.3.2. Metallic and non-metallic character  6.3.3. Electronegativity  6.3.4. Reactivity of the elements  6.4. Alkali metals and their properties
  7. Chemical bond  7.1. Why do atoms form bonds?  7.2. Types of chemical bonds  7.2.1. Ionic bond  7.2.2. Covalent bond  7.2.3. Metal Bond  7.3. Properties of Ionic and Covalent Compounds  7.4. Intermolecular forces
  8. Chemical reactions  8.1. Introduction to Chemical Reactions  8.2. Signs of a chemical reaction  8.3. Types of Chemical Reactions  8.3.1. Combination Reactions  8.3.2. Decomposition reactions  8.3.3. Displacement reactions  8.3.4. Double displacement reactions  8.3.5. Combustion reactions  8.4. Law of conservation of mass  8.5. Balancing simple chemical equations
  9. Acids, Bases and Salts  9.1. Definition of Acid and Base  9.2. Properties of Acids  9.3. Properties of bases  9.4. pH Scale and Indicators  9.5. Neutralization reactions  9.6. Common Acids and Bases in Everyday Life  9.7. Preparation and use of salts  9.8. Strong and weak acids and bases
  10. Solutions and Solubility  10.1. Definition of Solution  10.2. Components of the solution  10.2.1. Solvent  10.2.2. solute  10.3. Factors Affecting Solubility  10.4. Concentration of solutions  10.5. Saturated and unsaturated solutions  10.6. Colloids and suspensions  10.7. Solubility curve and its interpretation
  11. Air and atmosphere  11.1. Composition of air  11.2. Properties of gases in the air  11.3. Importance of Oxygen and Carbon Dioxide  11.4. Air pollution and its effects  11.5. Greenhouse effect and global warming  11.6. Ways to reduce air pollution  11.7. Ozone layer and its importance
  12. Water and its importance  12.1. Properties of Water  12.2. Water as the universal solvent  12.3. Importance of water for life  12.4. Water pollution and its effects  12.5. Water Purification  12.5.1. Filtration  12.5.2. boil  12.5.3. Chlorination in water purification  12.5.4. reverse osmosis  12.6. Hard and soft water  12.7. Water cycle and its importance
  13. Fuel and energy  13.1. Types of fuel  13.1.1. Fossil fuels  13.1.2. Renewable energy sources  13.2. Combustion and energy release  13.3. Global warming and its effects  13.4. Alternative sources of energy  13.5. Ways to conserve energy
  14. Metals and Nonmetals  14.1. Physical and chemical properties of metals  14.2. Physical and Chemical Properties of Non-Metals  14.3. Difference Between Metals and Nonmetals  14.4. Uses of metals and nonmetals  14.5. Corrosion of metals and its prevention  14.6. Alloys and their importance
  15. Plastics and polymers  15.1. Natural and synthetic polymers  15.2. Properties of plastics  15.3. Biodegradable and Non-Biodegradable Plastics  15.4. Environmental impact of plastic  15.5. Recycling and waste management in plastics and polymers  15.6. Daily Uses of Polymers
  16. Introduction to Organic Chemistry  16.1. Basic definitions of organic chemistry  16.2. Carbon Compounds in Daily Life  16.3. Hydrocarbons  16.4. Simple functional groups (alcohols and carboxylic acids)  16.5. Importance of organic compounds in industry

Grade 7 → Matter and its properties → States of matter ↓


Gaseous state


Matter is everything you can see, touch, and feel. It is what makes up all the objects around us. Matter exists in three main states: solid, liquid, and gas. In this explanation, we will focus on the gas state, which is characterized by unique properties and behaviors compared to the other two states. Let's learn what the gaseous state is, how it behaves, and how it differs from solids and liquids.

What is gaseous state?

A gas is a state of matter in which the particles are spread out and not bound together. Gas particles move freely at high speeds and can expand and fill any container they are placed in. This is different from solids, where the particles are tightly packed, and liquids, where the particles are loosely bound but still maintain a uniform volume.

Properties of gases

Gases have several special properties that are different from those of solids and liquids:

  • Indefinite shape and volume: Unlike solids which have a definite shape and volume, gases have no definite shape or volume. They expand to take the shape of the container they are in.
  • Compressibility: Gases are highly compressible, which means you can press them into a small volume with enough pressure. This is because the particles are far apart and have room to get close to each other.
  • Diffusion: Gases can easily mix with other gases, and spread evenly without requiring agitation.
  • Low density: Gases have a low density compared to solids and liquids. This low density is due to the large amount of space between the particles.
  • Exerts pressure: Gas particles collide with the walls of their container, exerting pressure. This pressure is an important property of gases because it affects how gases behave under different conditions, such as inside a balloon or in the atmosphere.

Molecular picture of gases

To better understand gases, it is helpful to visualize what is happening at the molecular level. Imagine gas particles as tiny spheres that are constantly moving in all directions. Here is a simple example:

In this diagram, the blue circles represent gas particles, and the red lines represent the path they can travel. These particles are moving very fast and are very far from each other, which means the gases can spread out and fill the available space.

Pressure in gases

The pressure exerted by a gas results from the gas particles colliding with the walls of the container. These collisions create a force over an area, which is experienced as pressure. This principle is understood by the formula:

Pressure (P) = Force (F) / Area (A)

Here, P stands for pressure, F stands for force, and A stands for the area over which the force is applied. Standard atmospheric pressure is often measured using units called atmospheres (atm) or pascals (Pa).

The concept of pressure is important in a variety of real-world applications, such as understanding how weather forms, how we breathe, and how vehicle tires hold air.

Temperature and kinetic energy

The temperature of a gas is directly related to the kinetic energy of its particles. Higher temperatures mean more kinetic energy and faster-moving particles. This relationship means that when you heat a gas, its particles move faster and expand more, which increases the pressure of the gas if the volume is not allowed to expand.

Low temperature High temperature

In the above simplified illustration, the orange circle represents a gas particle at a lower temperature, which is moving slower than the red circle, which represents a particle moving faster at a higher temperature.

Boyle's law

Boyle's law describes the relationship between the pressure and volume of a gas at a constant temperature. It says:

P₁V₁ = P₂V₂

In this equation, P₁ and V₁ are the initial pressure and volume, while P₂ and V₂ are the final pressure and volume. Boyle's law shows that if you decrease the volume of a gas and keep the temperature constant, the pressure will increase, and vice versa.

Charles's law

Another important gas law is Charles's law, which relates volume and temperature, and states:

V₁/T₁ = V₂/T₂

Here V₁ and T₁ are the initial volume and temperature, while V₂ and T₂ are the final volume and temperature. This law states that if you increase the temperature of a gas and keep the pressure constant, the volume will increase.

Real examples of gases

Understanding the gaseous state has many practical applications:

  • Balloon: When you inflate a balloon, you fill it with air, which is a mixture of gases. The balloon expands because of the pressure of the air.
  • Breathing: The human lungs work based on the principles of gas behaviour. Inhalation increases the volume of the lungs and decreases the pressure, drawing air in; exhalation decreases the volume, increasing the pressure and forcing air out.
  • Refrigeration: Refrigerators and air conditioners work by compressing and expanding gases, cooling interior spaces due to changes in temperature and pressure.
  • Aerosol cans: These cans use compressed gases to spray substances such as deodorant or paint, then they are sprayed out of a nozzle.

Conclusion

The gaseous state is fascinating and plays an important role in everyday life and scientific studies. From the simple act of breathing to understanding complex weather systems, gases are everywhere and constantly affect us. Understanding the basics of how gases work provides insight into the natural world and gives us the knowledge to effectively use gases in technology and daily life.


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Gaseous state

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