Chemical Reactions and Equations

Chemical Reaction and Equation

• A chemical reaction involves two or more reactants combining to form a product or new substance.

  • Example:
    A + B
    ightarrow AB

Physical vs Chemical Changes

• Physical Change:

  • Usually reversible.

  • Interchanging possible; new substance is not formed.

  • Example: Melting of ice.

• Chemical Change:

  • Irreversible; interchanging is not possible.

  • New substance is formed through a chemical reaction.

  • Example: Rusting.

Indicators of a Chemical Reaction

• Change in state

• Change in color

• Change in temperature

• Evolution of gas

• Formation of precipitate

  • A precipitate is an insoluble substance formed in a chemical reaction.

Definitions

• Reactant: A substance that undergoes a reaction to form products.

• Product: A substance that is formed after a reaction.

Skeletal Equations

• A skeletal equation shows the reactants and products but is not balanced.

  • Example:
    Mg + O_2
    ightarrow MgO

Importance of Balancing Equations

• Balancing is necessary to satisfy the Law of Conservation of Mass.

  • Mass cannot be created or destroyed in a chemical reaction.

  • Example of a balanced equation:
    2H2 + O2
    ightarrow 2H_2O

Symbols for States of Matter

• (g) = gaseous

• (aq) = aqueous

• (s) = solid

• (l) = liquid

Types of Chemical Reactions

1. Combination Reaction

   • Two or more reactants form a single product.

   • Example:
     2Mg + O_2
     ightarrow 2MgO

2. Decomposition Reaction

   • A single reactant breaks down into two or more products.

   • Example:
     AB
     ightarrow A + B

   • Thermal Decomposition: Heat is required to break down the substance.

     • Example:
       Zn + H2SO4
       ightarrow ZnSO4 + H2 + Heat

3. Displacement Reaction

   • More reactive element displaces a less reactive element from its compound.

   • Single Displacement and Double Displacement reactions fall under this category.

4. Oxidation and Reduction

   • Oxidation: Loss of electrons or increase in oxidation state.

   • Reduction: Gain of electrons or decrease in oxidation state.

Examples of Oxidation and Reduction

• Respiration:

  • Example:
    C6H{12}O6 + 6O2
    ightarrow 6CO2 + 6H2O + Energy

• Combustion of Natural Gas:

  • Example:
    CH4 + 2O2
    ightarrow CO2 + 2H2O + Heat

Endothermic and Exothermic Reactions

• Endothermic Reaction: Absorbs heat.

• Exothermic Reaction: Releases heat.

Special Reaction Types

• Electrolysis: Uses electricity to decompose substances.

• Photolysis: Uses light energy to decompose substances.

Conclusion

• Understanding chemical reactions and their equations is crucial in chemistry for predicting the behavior of substances during a reaction, their classifications, and energy changes involved.