Question

The equation for water is H2 +O2 → H2O. To balance the equation, which coefficient should be placed in front of H2 and H2O?

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Answer 1

To balance the equation for the formation of water (H2O) from hydrogen (H2) and oxygen (O2), we start with the unbalanced equation:

\[ \text{H}_2 + \text{O}_2 \rightarrow \text{H}_2\text{O} \]

1. **Count the number of atoms on each side:**
- **Reactants:**
- H: 2 (from H2)
- O: 2 (from O2)
- **Products:**
- H: 2 (from H2O)
- O: 1 (from H2O)

2. **Balancing the equation:**
- The number of hydrogen atoms is already balanced, but the oxygen atoms are not. To balance the oxygen (O), we need 2 oxygen atoms in the products.
- Since each water molecule (H2O) contains 1 oxygen atom, we need 2 water molecules to have 2 oxygen atoms:

\[ \text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O} \]

3. **Adjusting the hydrogen coefficient:**
- Now, with 2 molecules of water, we have 4 hydrogen atoms (2 x H2O) on the right side, so we need to place a coefficient of 2 in front of H2 to balance the hydrogen:

\[ 2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O} \]

Now the equation is fully balanced.

**Final balanced equation:**

\[ 2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O} \]

**Coefficients placed:**
- Place **2** in front of H2 and H2O.

So, the answer is **2**.