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 ↓


Gases and Gas Laws


Gases are one of the fundamental states of matter, along with solids and liquids. In this topic, we'll learn what gases are, how they behave, and the laws that govern their behavior. We'll take a closer look at how gases differ from other states of matter, their unique properties, and the important gas laws that scientists use to predict their behavior.

What are gases?

Gases are a state of matter that consists of tiny particles called atoms or molecules that are widely dispersed and move around freely. Unlike solids, which have a definite shape and volume, gases have neither of these. The molecules in gases are in constant motion, moving in straight lines until they collide with each other or with the walls of their container.

Properties of gases

Gases exhibit many unique properties. Here are some of the most important properties:

  1. Compressibility: Gases are easily compressible because their particles are far apart. When we apply pressure, the particles come closer and the volume of the gas decreases.
  2. Expandability: Gases expand to fill the available space. This means they take on the shape and volume of their container.
  3. Low Density: Gases have much lower density than solids and liquids because their particles are spread out.
  4. Diffusivity: Gases can diffuse, that is, particles can move from an area of high concentration to an area of low concentration.

Visual Example 1: Motion of Gas Particles

Let's imagine how gas particles move:

Gas Laws

Scientists have developed several laws that describe how gases behave. The most important of these are Boyle's Law, Charles' Law, and the Ideal Gas Law. Let's take a look at each of these in detail.

Boyle's law

Boyle's law states that the pressure of a gas is inversely proportional to its volume when the temperature remains constant. This means that if you increase the pressure, the volume decreases, and vice versa, provided there is no change in temperature.

The formula for Boyle's law is:

 P_1 cdot V_1 = P_2 cdot V_2

Here:

  • P_1 is the initial pressure
  • V_1 is the initial volume
  • P_2 is the final pressure
  • V_2 is the final volume

Lesson Example 1: Boyle's Law

If a gas occupies a volume of 2 litres at 1 atm pressure, what will be its volume if the pressure is increased to 2 atm, assuming the temperature remains constant?

    Use of Boyle's Law: 
    P 1 V 1 = P 2 V 2
    
    Let P 1 = 1 atm, V 1 = 2 L, and P 2 = 2 atm, solve for V 2 :
    
    (1 atm)(2 L) = (2 atm)(V 2 )
    V 2 = 1 L

Charles's law

Charles' law states that the volume of a gas is directly proportional to its temperature in Kelvin, provided the pressure remains constant. If the temperature increases, the volume increases and vice versa.

The formula for Charles's law is:

 frac{V_1}{T_1} = frac{V_2}{T_2}

Here:

  • V_1 is the initial volume
  • T_1 is the initial temperature in Kelvin
  • V_2 is the final volume
  • T_2 is the final temperature in Kelvin

Lesson Example 2: Charles's Law

The volume of a gas at 300 K is 3 litres. Assuming constant pressure, what will be its volume at 450 K?

    Use of Charles's Law: 
    v 1 /t 1 = v 2 /t 2
    
    Let V 1 = 3 L, T 1 = 300 K, T 2 = 450 K, solve for V 2 :

    (3 L)/300 K = V 2 /450 K
    V 2 = 4.5 L

Ideal Gas Law

The ideal gas law provides the relationship between pressure, volume, temperature, and the number of moles of a gas. It combines several gas laws into one formula, and is represented as:

 PV = nRT

Where:

  • P is the pressure
  • V is the volume
  • n is the number of moles of gas
  • R is the ideal gas constant (8.314 J/mol)
  • T is the temperature in Kelvin

Lesson Example 3: Ideal Gas Law

Calculate the volume occupied by 1 mole of an ideal gas at standard temperature (273 K) and pressure (1 atm).

    Use of Ideal Gas Law: 
    PV = nRT
    
    Let P = 1 atm, n = 1 mol, R = 0.0821 L atm/mol K, T = 273 K, solve for V:

    V = nRT/P
    V = (1 mol)(0.0821 L atm/mol K)(273 K)/(1 atm)
    V ≈ 22.4 L

Visual Example 2: Boyle's Law Change in Volume

Imagine compressing a cylinder of gas:


    
    
    
    Initial volume
    Compressed

Summary

To understand gases and how they behave, it is important to understand several basic concepts and principles. The properties of gases, such as compressibility and diffusivity, make them very different from solids and liquids. Gas laws such as Boyle's law, Charles' law, and the ideal gas law help us predict how gases will behave under different conditions. By understanding these laws and their applications, we can predict the changes in pressure, volume, and temperature of gases under different conditions.

These concepts are foundational to studying more advanced topics in chemistry and are applicable in real-world scenarios, including weather forecasting, designing air-powered devices, and even understanding how our lungs expand and contract when we breathe.


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Gases and Gas Laws

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