Law of Conversavation of Matter
This law states that matter can neither be created nor destroyed in an ordinary chemical reaction, but can change from one form to another.
What this implies is that when two elements or compound combine as a reactant to form a product, there's no loss of matter and the mass of the reactants must be equal to the mass of the product.
Given that
AlBr₃ + K₂SO₄ → KBr + Al₂(SO₄)₃
If we look closely at the above reaction, we would see that aluminuim is not balanced, potassium is also not balanced, bromine is not balance as well as sulphur and oxygen.
Let's put two moles attached to the AlBr₂ and three moles of K₂SO₄
2AlBr₃ + 3K₂SO₄ →
This would give us
6KBr + Al₂(SO₄)₃
If we add the two equations together,
2AlBr₃ + 3K₂SO₄ → 6KBr + Al₂(SO₄)₃
From the above, we have
2 atoms of Al on the reactant side and 2 atoms of Al on the product side
6 atoms of Br on the reactant side and 6 atoms of Br on the product side
6 atoms of K on the reactant side and 6 atoms of K on the product side
3 atoms of S on the reactant side and 3 atoms of S on the product side
12 atoms of O on the reactant side and 12 atoms of O on the product side