If you have worked out the MOLES of two reactants then the limiting reagent is the one with less moles. Sorted?
Well, it depends. If the reactants are in a 1:1 ratio then the above is true. But if the ratio is not equal then I'm afraid it's a bit more complicated.
Let's say reactants A and B have a ratio of 2:1 in the balanced equation.
If we have 0.020 moles of A and 0.015 moles of B which is the limiting reagent?
If we start with A we can see from the ratio that 0.02 moles of A will react with 0.01 moles of B.
As we started with 0.015 moles of B then not all of B has reacted.
Therefore B is in excess and A must be the limiting reagent.
If we start with B then we can see from the ratio that 0.015 moles of B will react with 0.030 moles of A.
As we only started with 0.02 moles A then we have insufficient moles of A. Therefore we can see that A is the limiting reagent.
So we can see that A is the limiting reagent even though we started with more moles of A than B.
