How do you determine how much of the excess reactant is left over? Also, how do you determine how much more of the limiting agent would you need to use up the excess?

Hint: In a chemical reaction if any chemical is left after completion of the reaction then it is called excess reactant and the chemical which is consumed totally during the chemical reaction is called limiting agent.

Complete answer:
- In the question it is asked how we can find how much amount of excess reagent is left and how much amount of limiting agent is needed to consume the excess reagent.
- To calculate the limiting agent we have to follow a few steps. This method is useful when the chemical reactions contain only two reactants.
a.Write the chemical equation which contains excess reagent and limiting agent.
b.Calculate the number moles of product from the first reactant.
c.Calculate the number moles of product from the second reactant.
d.Recognize the limiting reactant and the excess reactant in the chemical reaction.
e.Determine the mass of the excess reactant used up.
f.Determine the mass of the unused excess reactant.
g.Determine the mass of the limiting agent needed to react with the excess reactant.

Note:
After calculating the amount of excess reactant left in a chemical reaction we have added the respective amount of limiting agent to complete the particular chemical reaction. All these things are possible if we do the balancing of the chemical reaction properly.