The law of conservation of mass states that mass can neither be created nor destroyed, only transformed from one form to another. This means that the total mass of a closed system remains constant, regardless of the changes that occur within the system.

The law of conservation of mass can be expressed mathematically as follows:

```

mass of reactants = mass of products

```

This equation means that the total mass of the reactants in a chemical reaction must be equal to the total mass of the products. For example, if you burn a piece of wood, the mass of the wood will be converted into the mass of the ash and smoke. The total mass of the ash and smoke will be equal to the mass of the wood.

The law of conservation of mass is one of the fundamental laws of chemistry. It is used to balance chemical equations and to determine the amount of product that will be produced in a chemical reaction.