Representing Chemical Change

As we have already mentioned, a number of changes can occur when elements are combined with one another. These changes may either be physical or chemical. In this section we will look at chemical changes. One way of representing chemical changes is through balanced chemical equations. A chemical equation describes a chemical reaction by using symbols for the elements involved. For example, if we look at the reaction between iron \((\text{Fe})\) and sulfur \((\text{S})\) to form iron sulfide \((\text{FeS})\), we could represent these changes in a sentence, in a word equation or using chemical symbols:

• Sentence: Iron reacts with sulfur to form iron sulfide.

• Word equation: Iron \(+\) sulfur \(\rightarrow\) iron sulfide.

• Chemical symbols: \(\text{Fe} + \text{S} \rightarrow \text{FeS}\)

Another example would be:

• Sentence: Ammonia reacts with oxygen to form nitrogen monoxide and water.

• Word equation: Ammonia \(+\) oxygen \(\rightarrow\) nitrogen monoxide \(+\) water.

• Chemical symbols: \(4\text{NH}_{3} + 5\text{O}_{2} \rightarrow 4\text{NO} + 6\text{H}_{2}\text{O}\)

Compounds on the left of the arrow are called the reactants and these are needed for the reaction to take place. The compounds on the right are called the products and these are what is formed from the reaction.

In order to be able to write a balanced chemical equation, there are a number of important things that need to be done:

1. Know the chemical symbols for the elements involved in the reaction

2. Be able to write the chemical formulae for different reactants and products

3. Balance chemical equations by understanding the laws that govern chemical change

4. Know the state symbols for the equation

We will look at each of these steps separately in the next set of lessons.