Question

3 g of H2 react with 29 g of O2 to give H2O. Which is the limiting reagent? Calculate the amount of H2O formed? Calculate the amount of unreacted reactant left.

Answer 1

5 g of O2 will remain unreacted and H2 will be the limiting reagent ...and H20 will be formed 27g

Answer 2

The balanced equation for the above reaction is as follows:

2H2 + O2 = 2H2O

From the above equation it is clear that 2 mole H2 react with 1 mole O2

Molar mass of H2 = 2g

Molar mass of O2= 32 g

​This implies,

4 g H2 react with 32 g O2

3 g H2 reacts with = (32/4) x 3g of O2 gas
= 24 g
As the given amount of O2 is more than required therefore O2 is excess reagent and H2 is limiting reagent.

2 mole of hydrogen gas reacts to form 2 mole of water molecule therefore,
4 g of H2 produces = 36 g of water
So the amount of H2O produced by 3 g H2 = (36/4) x 3
= 27 g
Hence, 27 g of water will be produced during the recation

As, 24 g of oxygen has been utilised during the recation and 29 g of oxygen was supplied therefore amount of oxygen gas left is (29-24) = 5g

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