Understanding Chemical Equations

What chemical equations represent

Scientists use symbols in chemical equations to show what reactant(s) and product(s) are involved in a chemical reaction, what direction the reaction proceeds in, what physical states the reactant(s) and product(s) are in and what reaction conditions are involved (e.g. temperature, presence of a catalyst, time etc). This helps scientists to understand chemical equations and how to apply the equation practically if they want to carry out the reaction to obtain a product (or group of products) for commercial and research purposes.

Step-by-step balancing method with chemical equation example 1

Step 1) Here is an example of the combustion of methane, CH₄ , which is an unbalanced equation:

CH₄​(g) + …O₂​(g) → CO_2​(g)+ …H₂​O(l)

(g) means the physical state of the chemical is in a gaseous state while (l) means the physical state of the chemical is in a liquid state. So methane, oxygen and carbon dioxide are in a gaseous state while water is in a liquid state.

The small number 4, which is called subscript 4, from CH₄ , means there are four Hydrogen atoms covalently bonded to a Carbon atom.

Subscript 2 from O₂ means there are two Oxygen atoms covalently bonded to each other.

Subscript 2 from CO₂ means there are two Oxygen atoms each covalently bonded to a Carbon atom.

Subscript 2 from H₂O means there are two Hydrogen atoms each covalently bonded to an Oxygen atom.

Step 2)

Next step I would do to balance the chemical equation is I would list the type of atoms and their number on the left hand side (LHS) of the equation and on the right hand side (RHS) of the equation.

CH₄​(g) + …O₂​(g) → CO_2​(g)+ …H₂​O(l)

Step 3)

I can see on the LHS there are 4 hydrogen atoms while on the RHS there are 2 hydrogen atoms. We can’t change subscript 2 on H₂​O to subscript 4 due to the way 2 hydrogen atoms are each bonded to an oxygen atom, we can instead double the number of water molecules to get 4 hydrogen atoms on the RHS. When we double the number of water molecules on the RHS, we also increase the number oxygen atoms on the RHS as well to get 4 oxygen atoms.

Step 4)

The last step is to now double the number of oxygen atoms on the LHS to get a total of 4 oxygen atoms.

Step 5)

So now the the complete balanced equation is:

CH₄​(g) + 2O₂​(g) → CO_2​(g)+ 2H₂​O(l)

What this equation tells the scientist is that 1 mole of methane molecule will react with 2 moles of oxygen molecules to produce 1 mole of carbon dioxide and 2 moles of water molecules. If you don’t know what a mole is, click on the following link below:

What is a mole in chemistry explained simply

Congratulations! If you have read this far and followed the steps without any difficulty, you have fully understood balancing the chemical equation for combustion of methane.

References:

Combustion of hydrocarbon fuels – Polluting the atmosphere – AQA – GCSE Chemistry (Single Science) Revision – AQA – BBC Bitesize