Chemical Equations & Balancing
The Language of Chemistry | Chapter 1, Section 3
1. What is a Chemical Equation?
A chemical equation is the shorthand representation of a chemical reaction using symbols and formulas of the substances involved.
$A + B \xrightarrow{\text{conditions}} C + D$
- Reactants: Substances that take part in the reaction (written on the Left).
- Products: New substances formed (written on the Right).
2. Balanced vs. Skeletal Equations
A Skeletal Equation is an unbalanced equation where the number of atoms of each element on both sides is not equal.
A Balanced Equation follows the Law of Conservation of Mass: Mass can neither be created nor destroyed. Thus, the total number of atoms of each element must be equal on both sides.
The Hit-and-Trial Method:
- Write the skeletal equation.
- Count atoms of each element on both sides.
- Start balancing elements that appear in the fewest places (usually metals first).
- Balance Oxygen and Hydrogen at the end.
- Ensure coefficients are in the simplest whole-number ratio.
3. Information Conveyed
| Symbol | Meaning |
|---|---|
| $(s), (l), (g)$ | Solid, Liquid, Gas state |
| $(aq)$ | Aqueous solution (dissolved in water) |
| $\Delta$ (Delta) | Heat is supplied |
| $\uparrow$ or $\downarrow$ | Gas evolved or Precipitate formed |
| $\rightleftharpoons$ | Reversible reaction |
4. Limitations of Equations
A simple equation does not tell us:
- The physical state (unless state symbols are added).
- The time taken for completion.
- The concentration of reactants.
- Whether heat is evolved or absorbed (unless specified as $+ Q$ or $- Q$).
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