Photochemical Reactions
Chemistry: Cambridge International GCSE Supplement, topic 10.3.5
Light in Photochemical Reactions
Light is a form of energy that can be used to activate many chemical reactions. Reactions caused by light are called photochemical reactions.
Rate
- Increasing the light intensity increases the rate of photochemical reactions.
Photosynthesis
- Photosynthesis is the chemical change that takes place in the leaves of green plants. Chlorophyll (green pigments) absorbs light, which allows carbon dioxide and water to react. This produces glucose and oxygen.
- The greater the light intensity, the faster the rate of photosynthesis.
- To calculate the rate of photosynthesis, we can observe the increase in the volume of oxygen gas with time.
Equations for photosynthesis
- Word equation: carbon dioxide + water + light energy → glucose + oxygen
- Chemical equation: 6CO₂ + 6H₂O → C6H₁₂O₆ + 6O₂
Test yourself on Photochemical Reactions
What do we call reactions caused by light?
Which of these are examples of photochemical reactions?