Balanced chemical equations
Word equations
A chemical reaction can be summarised using a word equationAn equation in which only the names of the reactants and products are used to model a reaction.:
sulfur + oxygen 鈫 sulfur dioxide
This shows that:
- sulfur and oxygen are the reactantA substance that reacts together with another substance to form products during a chemical reaction.
- sulfur dioxide is the productA substance formed in a chemical reaction.
Chemical equations
In a chemical equation, the names of substances are replaced by symbols and formulaA combination of symbols that indicates the chemical composition of a substance.:
S + O2 鈫 SO2
Conservation of atoms
atomThe smallest part of an element that can exist. are not created or destroyed in chemical reactions. This means the numbers of atoms of each elementA substance made of one type of atom only. in the reactants is the same as the numbers of atoms of each element in the products.
This law applies to ionic formulae too, even though there are large numbers of each type of ionElectrically charged particle, formed when an atom or molecule gains or loses electrons. present in an ionic compound.
The equation above (S + O2 鈫 SO2) is correct:
| Atoms in the reactants | Atoms in the products |
| 1 脳 S | 1 脳 S |
| 2 脳 O | 2 脳 O |
| Atoms in the reactants | 1 脳 S |
|---|---|
| Atoms in the products | 1 脳 S |
| Atoms in the reactants | 2 脳 O |
|---|---|
| Atoms in the products | 2 脳 O |
This also means that the total massThe amount of matter an object contains. Mass is measured in kilograms (kg) or grams (g). of the reactants must equal the total mass of the products. This is known as the law of conservation of massThe total mass of reactants before a reaction is equal to the total mass of products after a reaction, because no atoms can be created or destroyed so the mass must remain unchanged..