Compounds & Reactions
Chemical formulae, balancing equations
Compounds and Chemical Reactions
A compound is a substance made of two or more elements chemically bonded together. Chemical formulae use symbols: H2O (water), NaCl (salt), CO2 (carbon dioxide). In equations, atoms must balance on both sides.
Example
Balancing a Chemical Equation
Unbalanced: H2 + O2 -> H2O. Count atoms: left has 2H, 2O; right has 2H, 1O — not balanced. Balanced: 2H2 + O2 -> 2H2O. Count: left has 4H, 2O; right has 4H, 2O — balanced!
Note
Key Point
The law of conservation of mass states that matter cannot be created or destroyed. This is why equations must balance — same atoms exist before and after, just rearranged.
Key Vocabulary
CompoundA substance made of two or more different elements chemically bonded together
Chemical formulaA notation using symbols and numbers to represent a chemical substance
Balanced equationA chemical equation with equal numbers of each type of atom on both sides
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