Chemical Equation

Key Notes :

Definition:

  • A chemical equation is a symbolic representation of a chemical reaction using chemical formulas and symbols.
  • It shows the reactants (substances that undergo change) and products (new substances formed) in a reaction.

Structure of a Chemical Equation:

  • Reactants are written on the left-hand side (LHS).
  • Products are written on the right-hand side (RHS).
  • An arrow (→) separates the reactants and products, indicating the direction of the reaction.

Example:

H2 + O2 → H2O

Balancing a Chemical Equation:

  • A chemical equation must obey the Law of Conservation of Mass (mass cannot be created or destroyed in a chemical reaction).
  • The number of atoms of each element on the LHS must equal the number of atoms on the RHS.
  • Coefficients (numbers placed before formulas) are used to balance the equation.

Example:

Unbalanced:

H2 + O2 → H2O

Balanced:

2H2 + O2 → 2H2O

Types of Chemical Equations:

  • Skeletal Equation: Unbalanced equation showing only reactants and products.

H2+Cl2→HCl

  • Balanced Equation: Follows the Law of Conservation of Mass.

H2 + O2 → 2H2O

  • Ionic Equation: Represents only the ions involved in the reaction.

NaCl(aq) + AgNO₃(aq) → AgCl(s) + NaNO₃(aq)

Symbols and Notations in Chemical Equations:

  • (s): Solid
  • (l): Liquid
  • (g): Gas
  • (aq): Aqueous (dissolved in water)
  • Heat/Δ: Heat is supplied
  • ↑: Gas is evolved
  • ↓: Precipitate is formed

Importance of a Chemical Equation:

  • Provides a concise way to describe chemical reactions.
  • Indicates the proportions of reactants and products.
  • Helps in predicting the outcomes of reactions.

Steps to Balance a Chemical Equation:

  • Write the unbalanced equation.
  • List the number of atoms of each element on both sides.
  • Add coefficients to balance the number of atoms for each element.
  • Verify that all elements are balanced and the equation follows the Law of Conservation of Mass.

Limitations of a Chemical Equation:

  • Does not indicate the reaction conditions (temperature, pressure, catalysts).
  • Does not show the rate of the reaction.
  • Does not provide information about the physical states of reactants and products unless mentioned.

Examples of Balanced Equations:

  • Combustion of Methane:

CH4 + 2O2 → CO2 + 2H2O

  • Photosynthesis:

6CO2 + 6H2O → C6H12O6 + 6O2​

Applications:

  • Used in laboratory experiments and industrial processes.
  • Helps in stoichiometric calculations to determine the quantities of reactants and products.

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