Write the overall chemical equation for photosynthesis.
Topic: Equation for photosynthesis
Answer
6CO₂ + 12H₂O → C₆H₁₂O₆ + 6H₂O + 6O₂↑
(in the presence of SUNLIGHT and CHLOROPHYLL, written above and below the arrow)
THREE THINGS must appear or marks are lost: the equation must be BALANCED SUNLIGHT and CHLOROPHYLL must be written on the arrow — they are essential conditions, not reactants, so they never go on the left-hand side the arrow ↑ after O₂ shows that oxygen is released as a gas
WHY 12 WATER AND NOT 6: the simpler form 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ balances arithmetically but is chemically misleading. Twelve molecules of water are split during PHOTOLYSIS to supply the hydrogen and the oxygen, and six molecules of water are re-formed during the dark reaction — which is why water appears on BOTH sides. The 12-water form is the one ICSE expects.
It also makes an important point: the oxygen released comes from WATER, not from carbon dioxide — which was proved by experiments using radioactive oxygen-18 as a tracer.