Chemistry reaction

Question

If 10.0 g of hydrogen and 75.0 g of oxygen are exploded together in a reaction tube, how much water is projected? What other gas is found in the reaction tube (besides water vapor) after the reaction, and how much of this gas remains?

Answer 1

First, write the balanced equation for the reaction:

2H₂(g) + O₂(g) ===> 2H₂O(g)

Next, find if either H₂ or O₂ is limiting:

moles H₂ present = 10.0 g x 1 mole/2.02 g = 4.95 moles H₂ (moles H₂O produced = 4.95 moles)

moles O₂ present = 75.0 g x 1 mole/ 32.0 g = 2.344 moles O₂ (moles H₂O produced = 2 x 2.344 = 4.69 mol)

O₂ is limiting since it will run out first. This means that H₂ is present in excess.

Calculate mass of H₂O produced:

4.69 moles H₂O x 18 g/mole = 84.4 g H₂O produced

Finally, the gas that is left over is hydrogen (H₂). To determine how much, we subtract the amount used up from the amount initially present: 2.34 moles O₂ x 2 moles H₂/mole O₂ = 4.68 moles used

4.95 moles - 4.68 moles = 0.27 moles H₂ left over.

0.27 moles H₂ x 2.02 g/mole = 0.545 g of H₂ left over.