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Chemical Symbols, Formulae, and Equations

1. Chemical Symbols and Formulae

Chemical Symbols

A chemical symbol is a shorthand notation used to represent an element. Examples include:

• H for Hydrogen
• O for Oxygen
• Na for Sodium
• Cl for Chlorine
• Ca for Calcium

Chemical Formulae

A chemical formula represents the composition of a compound. It can be of two types:

• Empirical Formula: Simplest ratio (e.g., CH₂O for glucose).
• Molecular Formula: Actual number of atoms (e.g., C₆H₁₂O₆ for glucose).

2. Writing Chemical Formulae

Steps to write chemical formulae:

1. Identify the elements involved.
2. Determine their valencies.
3. Cross over the valencies to form subscripts.
4. Write the formula.

Examples:

• Sodium Chloride: NaCl
• Magnesium Oxide: MgO
• Iron (III) Chloride: FeCl₃

3. Writing Chemical Equations

A chemical equation represents a reaction:

Reactants → Products

It must be balanced to follow the law of conservation of mass.

4. Balancing Chemical Equations

Steps to balance an equation:

1. Write the unbalanced equation.
2. Count the atoms of each element.
3. Adjust coefficients to balance atoms.
4. Recheck the counts.

Examples of Balanced Equations

1. Combustion of Methane:
   CH4 + 2O2 → CO2 + 2H2O
2. Formation of Water:
   2H2 + O2 → 2H2O
3. Synthesis of Ammonia:
   N2 + 3H2 → 2NH3
4. Decomposition of Water:
   2H2O → 2H2 + O2
5. Reaction of Zinc with Hydrochloric Acid:
   Zn + 2HCl → ZnCl2 + H2
6. Reaction of Sodium with Water:
   2Na + 2H2O → 2NaOH + H2
7. Neutralization of HCl by NaOH:
   HCl + NaOH → NaCl + H2O
8. Reaction of Iron with Oxygen:
   4Fe + 3O2 → 2Fe2O3
9. Formation of Calcium Carbonate:
   CaO + CO2 → CaCO3
10. Displacement Reaction (CuSO₄ and Zn):
    CuSO4 + Zn → ZnSO4 + Cu

Conclusion

Chemical symbols, formulae, and equations are foundational to understanding chemistry. Writing and balancing equations ensures accurate representation of reactions and adheres to the law of conservation of mass. With practice, these concepts become intuitive and valuable for predicting chemical behavior.