IB Chemistry: Chemical Equations

IB Chemistry: Chemical Equations

1. Deduce chemical equations when all reactants and products are given.

• The process up there is basically a reaction. A reactant forms a product. We’re going to learn how to “deduce” a chemical equation when the reactants and products are BOTH given.
• A Chemical Reaction is basically a reaction between reactants to form products. A chemical reaction is represented either with the chemical formulas or the symbols involved in the reaction.

Let’s consider the combustion of Methane.

Chemical Equation

Symbolic Equation

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However, the symbolic equation above is slightly incorrect. If you translate the symbolic equation to the equation with words, you still get “Methane + Oxygen –> Hydrogen + Carbon Dioxide.” Then why is it wrong?

This is because the symbolic equation does not follow the Law of Conservation. Law of conservation is similar to Conservation of Energy, where energy is conserved. Basically, here what starts in the beginning must last till to the end. Speaking more formally, this means that each side of both the reactants and products must have the same number of every type of atom.

If we look at the reactant side CH4 + O2, there is 1 Carbon atom, 4 Hydrogen atoms and 2 Oxygen atoms.

• Carbon = 1.
• Hydrogen = 4.
• Oxygen = 2.

Now if we look at the products side, H2O + CO2, there are 2 Hydrogen atoms, (2+1=3) Oxygen atom 1 Carbon atom.

• Carbon = 1.
• Hydrogen = 2.
• Oxygen = 3.

Now, there’s an imbalance here. There are 2 Oxygen atoms on the reactant side, but 3 Oxygen atoms on the products side! There’s also an imbalance in hydrogen atoms! So what can we do? When I started learning Chemistry, here was what I did to solve the problem.

I wrote the equation like this:

This is quite wrong. Firstly, CH2 is not methane anymore…. Secondly, you can’t just go changing the subscript. However, you can add numbers in front of the substance, we call this the coefficient.

E.g.

• O2 can be changed to 2O2. This will essentially be 2x (2 oxygen atoms) = 4 oxygen atoms.
• H2O can be changed to 3H2O. This will essentially be 3 x 2= 6 hydrogen atoms and 3 x 1 = 3 oxygen atoms.

So let’s revisit the original equation and change the coefficients to make sure the individual atoms balance in terms of quantity on both the reactant and products side.

The original equation is:

Right now, there’s an imbalance of both oxygen and hydrogen atoms. There are four hydrogen atoms on the left, and two on the right.

2. Apply the state symbols (s), (l), (g) and (aq).

We can add state symbols next to the substances in a symbolic equation.

(s) = solid.

(l) = liquid.

(g) = gas

(aq) = aqueous (relating to or dissolved in water)