Question

what is the limiting reactant

  

Answer 1

We can understand this by taking an example only. Let us consider simple reaction.

HCl + NaOH --> NaCl + H₂O

according to above balanced equation 1 mole HCl reacts with 1mole NaOH. Suppose we have taken 1 g HCl and 2g NaOH as starting reactants. But reactions will go according to stoichiometric ratios only, not as per amount mixed.

calculate how many moles are present in both compounds, this information gives limiting reactant.

moles = mass of compound / molar mass of respective compound is the formula

moles HCl = 1g / 36.46 g/mol = 0.0274273176 moles = 0.0274 moles

moles NaOH = 2g / 39.997 g/mol = 0.05 moles

but according to balanced equation 1 mole HCl reacts with 1 mole NaOH only, here we have 0.0274 moles HCl & 0.05 moles NaOH. If we try to react NaOH with 0.05 moles completely we need 0.05 moles of HCl, but we does not have that much. Hence here HCl is said to be limiting reactant. This way we can do calculations. The remaining NaOH moles are left unreacted only.

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