What kind of change happens in following cases?
Milk is left at room temperature during summers.
Change: Milk gets curdled most of the time.
An iron girdle/pan/nail is left exposed to humid atmosphere.
Change: A brownish layer forms on iron girdle or pan or nail.
Grapes get fermented.
Change: Grapes develop a strange taste.
Food is cooked.
Change: Food becomes tastier and is easier to digest.
Food gets digested in our body.
Change: Food changes into simple nutrients.
Change: Food is oxidized to produce energy for the body.
What is common in all these changes is that a new substance is formed after the change. You have read in earlier classes that when a new substance is formed after a change, the change is called a chemical change. Chemical Reaction is another name for chemical change.
Let us do an activity to understand chemical reaction or chemical change.
Things You Need
A magnesium ribbon, pair of tongs, Bunsen burner, watch glass
- Hold the magnesium ribbon with a pair of tongs at one end.
- Burn another end of magnesium ribbon with the help of flame on Bunsen burner.
- Magnesium ribbon burns with white dazzling light.
- A powdery substance gets collected in watch glass.
- Smoke comes out of burning magnesium ribbon.
- There is a change in colour, which is shown by white dazzling light.
- Smoke shows a change in state from solid to gas.
- Combustion signifies change in temperature.
- Powdery substance shows a new substance is formed.
We can say that a chemical reaction involves all or any of the above changes. There can be a change in colour, change in state, change in temperature, etc. In all cases of chemical reaction, a new substance is formed.
Signs of Chemical Reaction
- Change of state of substance
- Change of colour of substance
- Evolution of heat
- Absorption of heat
- Evolution of gas
- Evolution of light
- Evolution of sound, etc.