Mix, Heat, Spark: Reaction Triggers
Explore conditions needed for chemical changes.
What this lesson covers
Why it matters
Grey iron filings and yellow sulphur sit mixed but unreacted. Heat them and they fuse into black iron sulphide — a brand-new substance. That is a chemical reaction.
Predict first
Iron and sulphur are mixed but stay unchanged. What makes them react into iron sulphide?
Many reactions need a trigger — energy such as heat (here), light or electricity. Heated, iron and sulphur combine into iron sulphide.
- Heating them — a trigger of energy — correct
- Just waiting; the reaction starts on its own
- Stirring the powders harder
What you do
Iron and sulphur sit mixed but unreacted. Apply heat — the trigger — and watch a brand-new black substance form — iron sulphide, nothing like the powders you mixed.
Check yourself
What form of energy triggers the decomposition of water during electrolysis?
Water is decomposed by passing an electric current — electrical energy is the trigger, just as heat triggers iron + sulphur.
What specific condition is required for carbon to react with oxygen to form CO₂?
Combustion of carbon (C + O₂ → CO₂) requires heat to initiate the reaction, observed as a red glow.
Why is diffused sunlight specified for the H₂ + Cl₂ reaction?
The reaction is explosive in direct light; diffused sunlight allows controlled formation of HCl.
- Electricity — correct
- Heat
- Sunlight
- Diffused sunlight
- Electricity
- Heat — correct
- A catalyst
- Direct light causes an explosion — correct
- Direct light stops the reaction
- Diffused light is cheaper