Question

Can you write a balanced equation for BCl3 (g)+H2O (l)-------> H3BO3 (s)+HCl (g)?

Answer 1

The balanced equation is BCl₃(g) + 3H₂O(l) →H₃BO₃(s) + 3HCl(aq)

The usual procedure is to balance all atoms other than H and O; then balance O; then balance H.

Start with most complicated-looking molecule in the equation. This looks like H₃BO₃.

1. Balance all atoms other than H and O.

Put a 1 in front of the H₃BO₃. We start with

BCl₃ + H₂O → 1 H₃BO₃ + HCl

Since we have fixed one B atom on the right, we need one B atom on the left. We put a 1 in front of the BCl₃.

1 BCl₃ + H₂O → 1 H₃BO₃ + HCl

2. Balance O.

We have fixed 3 O atoms on the right, so we need 3 O atoms on the left. We put a 3 in front of the H₂O.

1 BCl₃ + 3 H₂O → 1 H₃BO₃ + HCl

3. Balance H.

Now we have fixed 6 H atoms on the left, so we need 6 H atoms on the right. We already have 3 H atoms on the H₃BO₃. We need 3 more H atoms, so we place a 3 in front of the HCl.

1 BCl₃ + 3H₂O → 1 H₃BO₃ + 3 HCl

4. Check that Equation is Balanced.

Since every formula has a coefficient, we should now have a balanced equation. Let’s check:

On the left: 1 B; 3 Cl; 6 H; 3 O.
On the right: 6 H; 1 B; 3 O; 3 Cl.

Our balanced equation is

BCl₃(g) + 3H₂O(l) → H₃BO₃(s) + HCl(aq)

Note that the HCl is so reactive and so soluble in water that it will be present as HCl(aq), not as HCl(g).