It is important to familiarise yourself with word and chemical equations. You should also practice balancing word and chemical equations.
An equation has two parts: the reactant on the left, and the products on the right. Plus signs
+ denote the separation between different substances and arrow signs
–> separate reactant (left) and product (right) sides of the equation.
There are three things you have to consider:
- The Rule
The third option is especially true if there’s something above the arrow (e.g photosynthesis) or if it’s an acid/base reaction.
Take this neutralisation reaction of an acid and a base
CuCO₃ + 2HNO₃ –> Cu(NO₃)₂ + H₂O + CO₂
It’s already balanced (which is looked at in the next section), but more importantly, it respects the valency. As copper(II) has a valency of 2+ and nitrate has an overall valency of 1- we can use the crossover method and determine that we need two nitrate molecules to balance one copper atom.
Take this wonderful nice equation of photosynthesis.
sunlight carbon dioxide + water –––––––––––> glucose + oxygen chlorophyll
Without balancing, this would be
CO₂ + H₂O –> C₆H₁₂O₆ + O₂
But of course, this is impossible, because there is 1 carbon on the reactant side while there is 6 on the carbon side, and 3 oxygen on reactant side, and 8 oxygen on the product side, and 2 hydrogen on the reactant side, and 12 hydrogen on the product side.
We can use our knowledge from Maths and find a number that would multiply the atoms so the equation becomes balanced.
Now how about we place a 6 in front of all of the substances except for glucose…
6CO₂ + 6H₂O –> C₆H₁₂O₆ + 6O₂
Now we have on both sides:
- 6 carbon
- 18 oxygen
- 12 hydrogen
Yay! This is known as the law of conservation of mass.
The final thing to take consideration of is the rule. For acid/base reactions, you can test yourself on Quizlet here:
The subscript shows the number of atoms in a molecule. The coefficient shows the number of molecules. They both represent quantity.
H₂SO₄ means there are 2 hydrogen atoms, 1 sulfur atom and 4 oxygen atom in a molecule/substance
3H₂SO₄ means there are 3 molecules of sulfuric acid (also known as dihydrogen sulfur quadoxide) with 2 hydrogen, 1 sulfur and 4 oxygen in each. Therefore in total there is 6 hydrogen, 3 sulfur and 12 oxygen.