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Unit 1: Chemistry and Our Earth

Equations

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Reactants and products

The starting substances used in a reaction are reactants.

The new substances formed in a reaction are products.

In a chemical reaction, one or more new substances

are formed.

The arrow means change into. In a chemical reaction, all the reactants change into the products.

reactants products

It is difficult to reverse a chemical reaction and change the products back into the reactants.

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What is a symbol equation?

A symbol equation uses the formulae of the reactants and products to show what happens in a chemical reaction.

This equation shows that one atom of sulfur (S) reacts with one molecule of oxygen (O2) to make one molecule of sulfur dioxide (SO2).

A symbol equation must be balanced to give the correct ratio of reactants and products.

+ S O2 SO2

+

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Balancing equations activity

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Symbol equations – balanced or not?