Question

How do you write the equation for this reaction: Aluminium bromide and chlorine gas react to form aluminium chloride and bromine gas?

Answer 1

We have understood the definition of chemical equation in the first place. When this kind of question is asked we should write the balanced chemical equation instead of writing the unbalanced chemical reaction.
Chemical equation is the representation of a chemical reaction where the reactants react to give products.

Complete answer:
Chemical equation is the representation of a chemical reaction where the reactants react to give products. As mentioned above we should write the chemical equation which is balanced,
Firstly it is very important to know the law of conservation of mass which states that the atoms are neither created nor destroyed. In a chemical equation the substance that is left to the arrow is called reactant and the substance that is to the right of the arrow is called product. Applying the law of conservation of mass to a chemical, there is no atom destroyed from the reactant side nor created in the product, so the number of elements in the reactant is equal to the number of elements in the product. This is the theory behind balancing chemical equations.
Aluminium bromide + Chlorine gas $\to$ Aluminum chloride + Bromine gas
Aluminium bromide = $AlB{{r}_{3}}$
Chlorine gas =$C{{l}_{2}}$
Aluminum chloride = $AlC{{l}_{3}}$
Bromine gas = $B{{r}_{2}}$
Now let's write the chemical equation:
$AlB{{r}_{3}}+C{{l}_{2}}\to AlC{{l}_{3}}+B{{r}_{2}}$
It is an unbalanced chemical equation:
Let's try a trial and error method, where we will check if the number of elements in the reactant is equal to the number of elements in the product.
-There are 3 bromine atoms on the reactant side but there are only 2 bromine atoms in product. So, we can add 2 before $AlB{{r}_{3}}$ and 3 before $B{{r}_{2}}$. In order to balance the equation.
-There is 2 chlorine atom in reactant side and there are 3 chlorine atom in product side so, in order to balance it we can add 3 before $C{{l}_{2}}$ and 2 before $AlC{{l}_{3}}$.
Thus, the balanced chemical equation is :
$2AlB{{r}_{3}}+3C{{l}_{2}}\to 2AlC{{l}_{3}}+3B{{r}_{2}}$
This is the chemical equation.

Note:
We should write chemical equations which are balanced. The law of conservation of mass attributes for balancing a chemical equation. In a balanced chemical equation the number of particular elements in a reactant should be equal to the number of elements in the product.