10.3.9 — Photosynthesis: Symbol Equation
Past Paper Mastery Exam · 15 Questions · 29 Marks
The complete balanced equation for photosynthesis — your reference for this exam.
Questions 1–5 | 7 marks
Write the chemical formula for glucose.
💡 Hint: Glucose is a sugar with 6 carbons, 12 hydrogens and 6 oxygens.
Write the chemical formula for carbon dioxide.
💡 Hint: 1 carbon, 2 oxygens.
Write the chemical formula for water.
💡 Hint: 2 hydrogens bonded to 1 oxygen.
Write the chemical formula for oxygen gas as it appears in a balanced chemical equation.
💡 Hint: Oxygen exists as a diatomic molecule in nature.
Name the two reactants and two products in the photosynthesis reaction.
💡 Hint: Think: what goes IN to a leaf, and what comes OUT?
Questions 6–10 | 10 marks
Write the word equation for photosynthesis.
💡 Hint: Carbon dioxide + ? → ? + ?
Write the balanced symbol equation for photosynthesis. Include state symbols.
💡 Hint: Reactants are CO₂(g) and H₂O(l). Use the formula for glucose: C₆H₁₂O₆.
Which of the following is the correctly balanced equation for photosynthesis?
Show by atom-counting that the equation 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ is balanced.
💡 Hint: Count C, H, and O atoms on both sides of the equation.
A student writes: CO₂ + H₂O → C₆H₁₂O₆ + O₂. Identify TWO errors in this equation and explain how to correct them.
💡 Hint: Check both the balancing numbers (coefficients) and the number of oxygens.
Questions 11–15 | 13 marks
Is photosynthesis an exothermic or endothermic reaction?
Explain, in terms of bond breaking and bond making, why photosynthesis is endothermic.
💡 Hint: Think about which process requires more energy: breaking or making bonds in this reaction.
What is the source of energy that drives photosynthesis? Explain how this energy is used in the reaction.
💡 Hint: Look at the conditions written above the arrow in the full equation.
Draw and label an energy profile diagram for photosynthesis. Indicate the activation energy and the overall energy change.
💡 Hint: Endothermic reactions have products at a HIGHER energy level than reactants.
Reference: Energy Profile for an Endothermic Reaction
A student states: 'Photosynthesis and respiration are exact opposites of each other.' Evaluate this statement using balanced equations and energy changes.
💡 Hint: Write both equations and compare reactants, products, and energy direction.
🔬 Examiner's Final Briefing
Key patterns that lose marks on photosynthesis equation questions:
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