biochemical calculation

Question

The measured volumes of hydrogen (4 dm3) and chlorine (3 dm3) were mixed together, then the reaction was started. Calculate the volume of the gases after the reaction.

Answer 1

Look at the balanced equation:

H₂(g) + Cl₂(g) ==> 2HCl(g)

Assuming temperature and pressure are constant, volumes can replace moles in such an equation. Since Cl₂ is present at 3 dm³ and H₂ is present at 4 dm³ (and the mole ratio is 1:1), this makes Cl₂ limiting. It will be used up, leaving some HCl left over. We can use an ICE table to visualize this...

H₂(g) + Cl₂(g) ==> 2HCl(g)

4...........3..................0..............Initial

-3........-3.................+6.............Change

1...........0..................6.............Equilibrium

So, at equilibrium, (after the reaction), volume will be 1 dm³ of H₂ + 6 dm³ of HCl = 7 dm³ total