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 ↓


Changes in the states of matter


Matter is all around us. Everything you see, touch, and interact with is made of matter. Matter can exist in different forms, such as solid, liquid, gas, and plasma. Understanding how matter changes from one state to another is fundamental in chemistry. This includes processes such as melting, freezing, evaporation, condensation, sublimation, and deposition. In this explanation, we'll dive deeper into each of these processes and how they affect the states of matter.

What are the states of matter?

States of matter are the different forms in which matter exists. The most common states we encounter everyday are solid, liquid, and gas. There is also a less common state called plasma. Let's take a closer look at these states:

  • Solid: The particles in a solid are tightly bound to each other. They have a definite shape and volume. For example, ice is the solid form of water.
  • Liquids: Particles in a liquid are still close together but can move freely. Liquids have a fixed volume but take the shape of their container. An example of this would be liquid water.
  • Gas: The particles in a gas are spread out and move freely at high speeds. Gases have no definite shape or volume. They take the shape and volume of their container. Water vapor is an example of a gas.
  • Plasma: A less common state of matter composed of charged particles. Plasma can be found in stars, including the Sun. It is not commonly found in normal Earth conditions.

Understanding changes in states of matter

Changes in states of matter, also called phase changes, occur when the energy in a system changes. This happens by the addition or removal of heat. Each change of state involves a different amount of energy and occurs at a specific temperature for each substance.

Melting

Melting is the process of changing from a solid to a liquid. This happens when the solid receives enough energy, usually in the form of heat, to break the bonds that hold the particles in a fixed position. The temperature at which this happens is called the melting point.

Example: Consider a piece of ice. When ice is exposed to heat, it begins to absorb energy. When enough energy is absorbed, the ice melts and turns into water.

H 2 O(solid) + heat → H 2 O(liquid)

Solidify

Freezing is the opposite of melting. It is the process of changing from a liquid to a solid when energy is removed from a liquid. The temperature at which this occurs is called the freezing point.

Example: When liquid water is placed in a freezer, it loses energy and turns into ice.

H 2 O(liquid) - heat → H 2 O(solid)

Evaporation

Vaporization is the process of changing from a liquid to a gas. This can happen in two ways: boiling and evaporation.

  • Boiling: This occurs when a liquid reaches its boiling point and rapidly turns into a gas.
  • Evaporation: This occurs at the surface of the liquid and can even occur at temperatures below the boiling point.

Example: When water is heated on the stove, it eventually begins to boil and turns into steam.

H 2 O(liquid) + heat → H 2 O(gas)

Evaporation

Condensation is the process of changing from a gas to a liquid. It occurs when gas particles lose energy and combine together to form a liquid. Condensation is the reverse of evaporation.

Example: As it cools overnight, water vapor in the air forms dew on the grass.

H 2 O(gas) - heat → H 2 O(liquid)

Sublimation

Sublimation is the change from solid state to gas directly, without going through the liquid state. It occurs when the particles of a solid gain enough energy to be released from the solid state.

Example: Dry ice, which is solid carbon dioxide, sublimes at room temperature to form carbon dioxide gas.

CO 2 (solid) + heat → CO 2 (gas)

Deposit

Deposition is the reverse of sublimation. It is the process of changing directly from a gas to a solid. It occurs when gas particles lose a significant amount of energy and settle into the solid state.

Example: Ice forms on cold surfaces by deposition. Water vapour present in the air turns directly into ice without first becoming a liquid.

H 2 O(gas) - heat → H 2 O(solid)

Energy and phase changes

It is important to understand the energy involved in changing states of matter. Each phase change requires or releases energy, known as latent heat. Phase changes involve two types of latent heat:

  • Latent heat of fusion: The energy required to change a solid into a liquid at its melting point, or the energy released when a liquid becomes a solid at its freezing point.
  • Latent heat of vaporization: The energy required to change a liquid into a gas at its boiling point, or the energy released when a gas changes into a liquid during condensation.

Real-life applications

Understanding phase changes is important for a variety of real-life applications. Let's take a look at two examples:

Refrigeration

Refrigerators use the concept of phase change to keep food cool. The refrigerant, which is the substance used for cooling, changes repeatedly from liquid to gas and back to liquid inside the fridge. During this process, it absorbs heat from the interior of the fridge, keeping it cool.

Weather patterns

Weather patterns are strongly influenced by the phase changes of water. For example, the formation of clouds, rain, and snow involves the condensation of water vapor into liquid droplets or ice crystals.

Conclusion

Changes in the states of matter are fundamental processes in chemistry and everyday life. These changes involve the addition or removal of energy, leading to phenomena we regularly observe. By understanding how matter transitions between solid, liquid and gaseous states, we gain insight into the behaviour of the substances around us, from ice melting to water boiling. It also helps us unlock technological innovations and better understand natural phenomena.


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Changes in the states of matter

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