What quantity of hydrogen gas is formed when 0.85 g of lithium reacts with water according to the following balanced equation? 2Li + 2H2O → 2LiOH + H2

Answer 1

First you need to convert the 0.85 grams of lithium to moles by dividing by its molar mass.

0.85 g Li X (1 mol/6.94 g) = 0.12 mol Li

Since you are looking for hydrogen, you then multiply by the mole ratio from the balanced equation.

0.12 mol Li X (1 mol H₂/2 mol Li) = 0.060 mol

Assuming we are looking for the mass of hydrogen gas, we then multiply by the molar mass of the hydrogen.

0.060 mol X (2.016 g/1 mol) = 0.12 g H₂'

If you are looking for volume, more information is needed about the pressure and temperature but you could use ideal gas law.