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Chemical Equations and Mole Ratios

Chemical equations & mole ratios

Balanced symbolic equations represent what happens in chemical reactions.
The reactants are written on the left of the arrow, whilst the products are written on the right of the arrow.
Reactants are the chemicals that react, and products are made (produced) in a chemical reaction.
A balanced always has the correct formulae for reactants and products
A balanced equation always has the same number of each type of atom on both sides of the equation.
E.g. 4Al + 3O₂ → 2Al₂O₃
The reactants are aluminium and oxygen, whilst the product is aluminium oxide.
4 mol of Al reacts with 3 mol of O₂ to produce 2 mol of Al₂O₃ (so a ratio of 4 : 3 → 2 )
There are 4 aluminium atoms on both sides of the equation, and 6 oxygen atoms on both sides of the equation.

There are four steps used to calculate masses of products or reactants from chemical equations.

Write a balanced equation for the reaction and determine the molar masses (M) of the known, M(known) and unknown, M(known).
Convert the mass of the known reactant or product to moles using n=m/M.
From the equations, deduce the mole ratio and the relationship between the n(known) and n(known) to determine the n(unknown).
Convert the n(unknown) into a mass using m=nM.

1.25g of magnesium ribbon is burnt in air to produce magnesium oxide, MgO. What mass of MgO will be produced?

Calculate the mass of chlorine gas required to produce 10g of sodium chloride from excess sodium metal.