Equations1
part of the In a Nutshell series on Adrian’s Study Club
Table of Contents
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:
- Valency
- Balancing
- 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.
Valency
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.
Balancing
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.
Rule
The final thing to take consideration of is the rule. For acid/base reactions, you can test yourself on Quizlet here:
Difference between subscript and coefficient
The subscript shows the number of atoms in a molecule. The coefficient shows the number of molecules. They both represent quantity.
Example
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.