CIE IGCSE Chemistry Resources
REVISION NOTES TOPIC QUESTIONS PAST PAPERS
EXAM TIP
When answering questions on the effect of concentration on the rate of reaction, you
should mention that there are more particles per unit volume (usually cm
3
) and this
causes an increase in the rate of collisions.
EXTENDED ONLY
Photochemistry
Photochemical reactions
• These reactions occur only when light is present
• The greater the intensity of ultraviolet light then the greater the rate of reaction
• E.g. the substitution of hydrogen atoms in methane by chlorine:
CH
4
+ Cl
2
→ CH
3
Cl + HCl
Silver salts in photography
• Black and white photography film surfaces contain crystals of silver bromide
• When exposed to light they decompose to silver:
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