Grade 8
  1. Introduction to Chemistry  1.1. Nature and scope of chemistry  1.2. Importance of chemistry in daily life  1.3. Chemistry and its relation with other sciences  1.4. The role of chemistry in industry, medicine and the environment  1.5. Scientific investigation and experimental methods in chemistry
  2. Matter and its properties  2.1. Definition and classification of matter  2.2. Physical and chemical properties of matter  2.3. Law of conservation of matter  2.4. Extensive and Intensive Properties of Matter  2.5. Kinetic molecular theory of matter  2.6. States of matter: solids, liquids, gases, plasmas, and Bose-Einstein condensates  2.7. Changes in state and energy are involved  2.8. Diffusion and Brownian motion
  3. Elements, Compounds, and Mixtures  3.1. Definition and differences between elements, compounds, and mixtures  3.2. Atomic Structure and Atomic Number  3.3. Chemical symbols and formulas  3.4. Trends in the Periodic Table (Groups and Periods)  3.5. Classification of Elements: Metals, Nonmetals and Metalloids  3.6. Rare Earth Elements and Transition Metals  3.7. Types of mixtures: homogeneous and heterogeneous  3.8. Separation of Mixtures Using Physical and Chemical Methods
  4. Separation Techniques  4.1. Filtration, Sedimentation and Decantation  4.2. Evaporation and crystallization  4.3. Distillation and Fractional Distillation  4.4. Chromatography and its applications  4.5. Sublimation in the purification of compounds  4.6. The role of centrifugation in biochemical processes
  5. Atomic Structure  5.1. Dalton's atomic theory  5.2. Structure of the atom: protons, neutrons and electrons  5.3. Bohr's atomic model  5.4. Introduction to Quantum Mechanical Model  5.5. Electron Configuration and Energy Levels  5.6. Excitation and emission spectra  5.7. Isotopes and their applications
  6. Periodic Table and Chemical Trends  6.1. History and Development of the Periodic Table  6.2. Modern periodic law  6.3. Periodicity and trends in atomic and ionic sizes  6.4. Ionization Energy, Electron Affinity and Electronegativity  6.5. Introduction to Lanthanides and Actinides  6.6. Application of periodic trends in chemistry
  7. Chemical Bonding and Molecular Structure  7.1. Types of chemical bonds: ionic, covalent and metallic bonds  7.3. Polar and Nonpolar Molecules  7.4. Hydrogen bonding and its applications  7.5. Intermolecular forces: dipole-dipole, London dispersion force
  8. Chemical Reactions and Stoichiometry  8.1. Chemical Equations and Balance  8.2. Types of Chemical Reactions: Combination, Decomposition, Displacement and Redox  8.3. Introduction to stoichiometry and the mole concept  8.4. Limiting reactant in chemical equations  8.5. Reaction rate, catalyst, and factors affecting reaction rate
  9. Acids, Bases and Salts  9.1. Definition and Properties of Acids and Bases  9.2. Strong vs. Weak Acids and Bases  9.3. pH Scale and pH Calculation  9.4. Neutralization reactions  9.5. Buffer solutions and their importance  9.6. Applications of Acids, Bases and Salts in Daily Life
  10. Solutions and Solubility  10.1. Definition of Solution, Solute, and Solvent  10.2. Factors Affecting Solubility  10.3. Concentration units: molarity and molality  10.4. Saturated, unsaturated and supersaturated solutions  10.5. Concept of osmosis and reverse osmosis  10.6. Concentrative properties of solutions
  11. Gases and Gas Laws  11.1. Properties of gases  11.2. Introduction to Ideal and Real Gases  11.3. Boyle's Law, Charles' Law and Avogadro's Law  11.4. Ideal Gas Equation and Its Applications  11.5. Application of Gas Laws in Real Life
  12. Thermochemistry and energy transformation  12.1. Energy in Chemical Reactions  12.2. Exothermic vs. Endothermic Reactions  12.3. Heat and Enthalpy Changes  12.4. Calorimetry and heat transfer in reactions
  13. Metals and Nonmetals  13.1. Physical and Chemical Properties of Metals and Nonmetals  13.2. Reactivity Series of Metals  13.3. Corrosion and its prevention  13.4. Extraction of metals from ores  13.5. Uses of metals and non-metals in daily life
  14. Introduction to Organic Chemistry  14.1. Characteristics of carbon and organic compounds  14.2. Functional groups and their importance  14.3. Simple Hydrocarbons: Alkenes, Alkenes and Alkynes  14.4. Isomerism in organic compounds  14.5. Introduction to polymers and their uses
  15. Environmental Chemistry and Sustainability  15.1. Green Chemistry Principles  15.2. Effects of Chemical Pollution on Ecosystems  15.3. Acid rain and its effects  15.4. Ozone layer depletion and global warming  15.5. Waste Management and Recycling in Chemistry

Grade 8 → Matter and its properties ↓


Changes in state and energy are involved


Matter is everything that has mass and occupies space. Everything we see around us is made of matter, and matter exists in different forms called states. The main states of matter are solid, liquid, and gas. There are also less common states such as plasma and Bose-Einstein condensates, but for simplicity, we'll focus on the first three. Understanding how matter changes from one state to another is fundamental in chemistry. In this lesson, we'll explore these changes of state and the energy involved in such processes.

Understanding the states of matter

Before we discuss state changes, let us briefly understand each state of matter:

  • Solid: In the solid state, matter has a definite shape and volume. The particles are close to each other and vibrate in place.
  • Liquid: In the liquid state, the substance has a fixed volume but takes the shape of its container. The particles are less tightly packed than in solids and can move around each other.
  • Gas: In the gaseous state, the matter has no definite shape or volume. The gas particles are far away from each other and move around freely.

State changes

Change of state refers to the transformation of matter from one state to another. These changes are physical, that is, there is no change in the chemical composition of the matter.

Melting - solid to liquid

Melting occurs when a solid substance changes into a liquid. This happens when a solid substance absorbs enough heat energy to break down the rigid structure of its particles. For example, when ice (solid water) absorbs heat, it melts and becomes liquid water.

        H 2 O (s) → H 2 O (l)

Freezing of ice - from liquid to solid

Freezing is the change from a liquid to a solid. This occurs when the liquid loses heat energy, and its particles slow down and form a rigid structure. For example, when water freezes, it becomes ice.

        H 2 O (l) → H 2 O (s)

Evaporation - liquid to gas

Vaporization occurs when a liquid changes into a gas. This can happen in two ways: evaporation and boiling. In vaporization, only the surface particles of the liquid gain enough energy to become a gas. In boiling, the particles inside the liquid gain enough energy.

        H 2 O (l) → H 2 O (g)

Consider the formation of steam from the boiling of water. As heat is applied, the particles move faster until they escape into the gas phase.

Condensation - gas to liquid

Condensation occurs when a gas turns into a liquid. This happens when the gas loses heat energy and its particles move closer together to become a liquid. Examples include water vapor condensing into dew on grass.

        H 2 O (g) → H 2 O (l)

Sublimation - solid to gas

Sublimation is the process in which a solid substance changes directly into a gas without becoming a liquid. Dry ice, which is solid carbon dioxide, is a common example. It sublimes at temperatures below the freezing point.

        CO 2 (s) → CO 2 (g)

Deposition - solid from gas

Deposition is the reverse of sublimation. Here, the gas changes directly into a solid. Frost formation on cold surfaces is an example of this, where water vapour becomes ice without becoming water.

        H 2 O (g) → H 2 O (s)

Energy changes involved in a change of state

Every change of state involves energy. Energy is either absorbed or released during these processes:

  • Endothermic processes: These are changes where energy is absorbed from the surrounding environment. Melting, evaporation, and sublimation are endothermic because they require the absorption of heat to overcome the attractive forces between particles.
  • Exothermic processes: These changes involve the release of energy into the surrounding environment. Solidification, condensation, and deposition are exothermic processes because they release heat when particles come closer to each other.

Visual example of melting

In the above illustration, you can see a solid (represented by a rectangle) absorbing energy and transforming into a liquid (represented by a circle).

Role of temperature and pressure in phase change

Changes in state are affected by temperature and pressure. Temperature measures the kinetic energy of particles. Increased temperature usually provides the energy needed for changes such as melting and vaporization.

On the other hand, pressure can affect the interaction of particles. For example, increasing the pressure on a gas can lead to condensation, as the particles come closer to each other.

Visual example of evaporation

Gas

In this simple example, as heat is added, the liquid becomes a gas, increasing the energy of the particles until they escape into the air.

Real-life examples and applications

Cooking

Cooking involves many different changes. Boiling water involves changing from a liquid to a gas. Freezing a dessert involves changing from a liquid to a solid. Cooking shows how heat energy changes the state of ingredients, affecting texture and taste.

Weather and the water cycle

The water cycle shows many phase changes. Evaporation from oceans, rivers and lakes turns water from liquid to gas, forming clouds (condensation). Rain involves going from gas to liquid. Snow and ice represent solid states formed by deposition or freezing.

Industrial uses

Industries also use these state changes. For example, distillation is used to purify liquids through evaporation and condensation. Freeze-drying food involves sublimation to remove water, which preserves food better.

Conclusion

Changes in state are fundamental and are all around us. From simple daily events to complex industrial processes, understanding the motion and interaction of particles in these states advances our understanding of the physical world. Whether it is the melting of ice in your drink or the mixing of gases in the atmosphere, changes in matter and energy transformations are constant and are essential in defining the properties of matter.


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Changes in state and energy are involved

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