Chemical reaction equation.

2H2 + O2 -> 2H2O

A chemical reaction equation is a symbolic representation of a chemical reaction. It shows the chemical formulas of the reactants and products of the reaction, as well as the stoichiometry of the reaction. The stoichiometry of a reaction refers to the relative amounts of reactants and products that are involved in the reaction.

Chemical reaction equations are typically written in the following format:

```
aA + bB → cC + dD
```

where A, B, C, and D are the chemical formulas of the reactants and products, and a, b, c, and d are the stoichiometric coefficients. The stoichiometric coefficients indicate the relative amounts of each reactant and product that are involved in the reaction. For example, the equation above indicates that 2 moles of A react with 3 moles of B to produce 4 moles of C and 5 moles of D.

Chemical reaction equations are used to represent a wide variety of chemical reactions, including:

- Acid-base reactions
- Combustion reactions
- Gas-phase reactions
- Solid-state reactions
- Oxidation-reduction reactions

Chemical reaction equations are essential for understanding the chemistry of a reaction, and they can be used to predict the products of a reaction and to calculate the amount of products that will be produced.