Symbolic equations can be used to summarise either physical or chemical change. Here we will focus on chemical change.

Let's consider the reaction between methane and oxygen: 

CH₄(g) + 2O₂(g) _↓ CO₂(g) + 2H₂O(l)

A chemical equation can give us the following pieces of information:

• types of atom involved
• numbers of atoms of each type
• how the atoms are associated with each other
• the physical state in which the atoms exist

As we saw in the case of CO₂ the formula of the compound does not indicate how the atoms in the molecule are arranged or, in this case, chemically bonded to each other.

The use of a model may help us understand this better. [INSERT CHEM_CI_07_ima)

If we were to write the formula out so it was a better representation of the above molecule we may write OCO. The challenge for students of chemistry is that they don't always gain an understanding of the way that the atoms or ions rearrange themselves because of the way that we represent change through chemical symbols. We present a shorthand version of the formula to them.

A second challenge for many students is making the link between the sub-microscopic arrangement of atoms and how they are represented in the chemical formula. You might like to reflect on the difficulties your students have when understanding and explaining chemical change.  

At this stage you may also want to subscribe to and explore the online Quantitative chemistry course.