Question

If 4.0 g of hydrogen and 10.0 g of oxygen are mixed according to the equation 2 h2 + o2 → 2 h2o, which is the limiting reagent?

Answer 1

From the equation, we can see that the molar ratio between hydrogen and oxygen is:
2 : 1

Next, we determine the moles of hydrogen and oxygen that are actually present using:
moles = mass / Mr

Hydrogen:
moles = 4 / 2 = 2

Oxygen:
10/32 = 0.3125

Therefore, it is evident that the moles of oxygen present, 0.3125, are less than those that are required for 2 moles of hydrogen, which is 1. This makes oxygen the limiting reactant, which is the one that limits the completion of a reaction.