On burning hydrogen in air, the colour of flame is — Hydrocarbons Chemistry Question

💡 Solution & Explanation

# Burning of Hydrogen in Air **Chemical Reaction:** $$2H_2 + O_2 \rightarrow 2H_2O$$ **Flame Color Explanation:** When hydrogen burns in air, the flame appears **pale blue** (or colorless with a pale blue tint). **Why this color?** - Hydrogen combustion produces $H_2O$ molecules and releases energy as heat (~286 kJ/mol) - The pale blue color comes from the **chemiluminescence** of $OH^*$ radicals (excited hydroxyl radicals) formed during combustion - These excited radicals emit light in the blue region of the visible spectrum as they return to ground state **Key Point:** The flame is quite **pale/faint** because hydrogen combustion doesn't produce soot or incandescent particles (unlike carbon-based fuels), so there's minimal visible light — only the subtle blue glow from $OH^*$ emission. **Without option list, B likely refers to:** "Pale blue" or "Blue" ✓