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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?