Question

Use the chemical reaction to answer the question. 2H2 + O2 — 2H2 O: There are four atoms of hydrogen (H) before the reaction. How many atoms of hydrogen are present after the reaction? (5; 4; 8; 2)

Answer 1

In the chemical reaction \( 2H_2 + O_2 \rightarrow 2H_2O \), we start with 4 atoms of hydrogen (since \( 2H_2 \) indicates there are two molecules of hydrogen, each containing 2 atoms).

After the reaction, we have the product \( 2H_2O \). In each water molecule (\( H_2O \)), there are 2 hydrogen atoms. Therefore, for 2 water molecules:

\[
2 \text{ H}_2O \times 2 \text{ H atoms/molecule} = 4 \text{ H atoms}
\]

So, there are still 4 atoms of hydrogen present after the reaction. The answer is:

**4**