SO3 + H2O → H2SO4

This is a chemical reaction where sulfur trioxide (SO3) reacts with water (H2O) to form sulfuric acid (H2SO4). Here are the steps to balance this equation:

1. Write down the unbalanced equation: SO3 + H2O → H2SO4

2. Balance the sulfur atoms first. There is one sulfur atom on both sides of the equation, so the sulfur is already balanced.

3. Next, balance the oxygen atoms. There are 3 oxygen atoms on the left side (in SO3) and 4 oxygen atoms on the right side (in H2SO4). To balance the oxygen atoms, you can add a water molecule (H2O) to the left side: SO3 + H2O → H2SO4 + H2O

4. Now, balance the hydrogen atoms. There are 2 hydrogen atoms on the left side and 4 hydrogen atoms on the right side. To balance the hydrogen atoms, you can add a water molecule (H2O) to the left side: SO3 + 2H2O → H2SO4 + H2O

5. Finally, simplify the equation by removing the extra water molecule from the right side: SO3 + 2H2O → H2SO4

So, the balanced chemical equation is: SO3 + H2O → H2SO4