Question

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Water is produced from the reaction of hydrogen and oxygen gas, according to the equation below. What is the excess reactant in the reaction of 4.2 moles of hydrogen with 3.0 moles of oxygen? 2H2(g) + O2(g) → 2H2O(l)

Answer 1

Answer: Oxygen is the excess reactant.

Explanation: $2H_2+O_2\rightarrow 2H_2O$

As can be seen from the given chemical equation, 2 moles of hydrogen gas react with 1 mole of oxygen gas.

4.2 moles of hydrogen gas react with$=\frac{1}{2}\times {4.2}=2.1mole$ of oxygen gas.

Thus hydrogen is the limiting reagent as it limits the formation of product. And oxygen is the excess reagent as it is present in excess. (3-2.1) = 0.9 moles of oxygen are left as such.