What do we mean by molar ratio?

The molar ratio is the ratio between the moles of different reactants and products in a balanced equation.


For example, in the equation: N2+ 3H2 ➔ 2NH3, the N2 : H2 molar ratio is 1:3.

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Give the 4 state symbols and describe what each symbol means.

(s) = solid

(l) = liquid

(g) = gas

(aq) = aqueous solution (dissolved in water)

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Describe, in terms of atoms, how to tell whether an equation is balanced.

A balanced equation should have the same number of atoms on the reactant and product sides of the equation.

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What 2 things must be the same in a balanced ionic equation?

1Same number of atoms of each element on each side of the equation.

2Same total charge of each side of the equation.

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What are the 3 forms of the formula that links mass, Mr and number of moles?

1mass = number of moles x Mr

2number of moles = Mr​mass​

3Mr = number of molesmass​

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What is a spectator ion?

A spectator ion is an ion that does not take part in a reaction.

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Describe the steps in obtaining the ionic equation from a full balaned symbol equation.

  1. Re-write the balanced symbol equation showing the formulae of all aqueous ions present.
  2. Cancel the spectator ions (ions that appear on both sides of the equation).
  3. Check ionic charges balance on both sides.

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What does it mean if a reactant is 'in excess’?

There is more than is needed, so there is some left over at the end of the reaction. In other words, there is an excessive amount.

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What is a 'limiting reactant’?

A reactant that all gets used up, and so limits how much product can be made (because there's none of that reactant left).

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