Which of the following reactions is possible according to Dalton's atomic theory?

• A. H_2O → H_2 + O
• B. C + O_2 → CO_3
• C. 2H_2 + O_2 → 2H_2O
• D. 2Na → Na + Na

Answer: (C)

Verified step by step guidance

1. Recall Dalton's atomic theory, which states that atoms are indivisible and indestructible in chemical reactions, and that atoms combine in simple whole-number ratios to form compounds.
2. Analyze the first reaction: \(\mathrm{H_2O \rightarrow H_2 + O}\). This reaction suggests water decomposes into hydrogen gas and atomic oxygen, but atomic oxygen (O) is highly reactive and does not exist freely under normal conditions; oxygen usually exists as \(\mathrm{O_2}\). Also, atoms should be conserved, so breaking water into \(\mathrm{H_2}\) and \(\mathrm{O}\) atoms violates the stable molecular form of oxygen.
3. Examine the second reaction: \(\mathrm{C + O_2 \rightarrow CO_3}\). Carbon monoxide trioxide (\(\mathrm{CO_3}\)) is not a stable or common compound under normal conditions, and this formula does not represent a simple whole-number ratio of atoms consistent with Dalton's theory.
4. Look at the third reaction: \(\mathrm{2H_2 + O_2 \rightarrow 2H_2O}\). This reaction shows hydrogen and oxygen gases combining in simple whole-number ratios to form water, a stable compound. This aligns perfectly with Dalton's atomic theory, conserving atoms and forming compounds with fixed ratios.
5. Consider the fourth reaction: \(\mathrm{2Na \rightarrow Na + Na}\). This reaction simply splits sodium atoms into individual sodium atoms, which is not a chemical reaction but rather a trivial rearrangement, and does not represent a meaningful chemical change according to Dalton's theory.