(40) GCSE Chemistry Revision "Balancing Chemical Equations"

Understanding Chemical Formulas

• Definition: A chemical formula represents the elements and the number of atoms in a compound.

• Example: Sodium carbonate (Na2CO3)

  • Elements present: Sodium (Na), Carbon (C), Oxygen (O)

  • Atom count:

    • Sodium: 2 atoms (indicated by the small 2)

    • Carbon: 1 atom (no number means one)

    • Oxygen: 3 atoms (indicated by the small 3)

Rules for Chemical Formulas

• Changing Small Numbers: You cannot change the small numbers in a chemical formula as it creates a different molecule.

• Using Large Numbers: Placing a large number in front of a formula indicates multiple molecules of that compound.

  • Example: 3Na2CO3 = 3 molecules of sodium carbonate.

Balancing Chemical Equations

• Balanced Equation Definition: An equation is balanced when the number of each type of atom on the left side (reactants) equals the number on the right side (products).

  • Example: Ca + Cl2 → CaCl2

    • Left Side: 1 Ca, 2 Cl

    • Right Side: 1 Ca, 2 Cl

    • This equation is balanced.

Steps for Balancing Equations

1. Count Atoms: Identify the number of atoms of each element on both sides of the equation.

2. Identify Imbalance: Look for elements with different atom counts on the reactants and products sides.

3. Use Large Numbers: To balance, add a large number in front of the compound needing adjustment.

   • Example: Balancing Na + I2 → NaI

     • Left Side: 1 Na, 2 I

     • Right Side: 1 Na, 1 I

     • Balance Iodine: Add 2 in front of NaI resulting in Na + I2 → 2NaI.

     • Now, balance Sodium: Add 2 in front of sodium (Na) to balance: 2Na + I2 → 2NaI.

Practice Examples

• First Practice: Balance the equation: CaO + HCl → CaCl2 + H2O

  • Calcium balanced: 1 Ca on both sides.

  • Oxygen balanced: 1 O on both sides.

  • Hydrogen: 1 H on left, needs adjustment for 2 H on right.

  • Chlorine: 1 Cl on left, needs adjustment for 2 Cl on right.

  • Final Balanced: CaO + 2HCl → CaCl2 + H2O.

• Second Practice: Balance the equation: Fe2O3 + CO → Fe + CO2

  • Left Side: 2 Fe, 3 O, 1 C

  • Right Side: 2 Fe, 1 C, 2 O

  • Add large number: 3 in front of CO2.

  • Final Balanced: Fe2O3 + 3CO → 2Fe + 3CO2.

Conclusion

• Balancing chemical equations requires counting atoms and adjusting with large numbers of compounds. The method outlined ensures systematic balancing to achieve equilibrium in chemical reactions.