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# Don't get left behind

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## Chapter summary

Presentation: VPeca

• A chemical equation uses symbols to describe a chemical reaction.

• In a chemical equation, reactants are written on the left hand side of the equation and the products on the right. The arrow is used to show the direction of the reaction.

• When representing chemical change, it is important to be able to write the chemical formula of a compound.

• The law of conservation of mass states that the mass of a closed system of substances will remain constant, regardless of the processes acting inside the system. Matter can change form, but cannot be created or destroyed.

• In any chemical reaction, the law of conservation of mass applies. This means that the total atomic mass of the reactants must be the same as the total atomic mass of the products. This also means that the total number of atoms of the reactants must be the same as the total number of atoms of the product.

• If the number of atoms of each element in the reactants is the same as the number of atoms of each element in the product, then the equation is balanced.

• If the number of atoms of each element in the reactants is not the same as the number of atoms of each element in the product, then the equation is not balanced.

• In order to balance an equation, coefficients can be placed in front of the reactants and products until the number of atoms of each element is the same on both sides of the equation.

• The state of the compounds in a chemical reaction can be expressed in the chemical equation by using one of four symbols. The symbols are g (gas), ℓ (liquid), s (solid) and aq (aqueous solutions). These symbols are written in brackets after the compound.