Classify the following changes into more than one category. Do This Activity HIN
Slow/Fast, Reversible/Irreversible/ Physical/Chemical
Change
Burning of an incense-stick
Freezing of water
Formation of biogas from cow dung
Bursting of a balloon
Heating of sugar in a pan
Lighting of electric bulb
Answers
Burning of an "incense stick" is not a "physical change" as it is a irreversible change. When an incense stick is burnt new substances ash and smoke are produced.
Freezing of water - The liquid water changes into solid water called ice. Only a change in state (from liquid to solid) takes place during the freezing of water to form ice, but no new substance is formed. So, the freezing of water (to form ice) is a physical change.
Formation of biogas from cow dung - Production of biogas is a chemical change . Because in biogas plant many gases released from cow dung and other animal waste .
Bursting of a balloon - It is a physical change because there is an increase in air pressure inside the balloon. When the balloon bursts then it becomes small in respect to when it was having air inside it.
Heating of sugar in a pan - Heating sugar melts it from solid to liquid state and it is a physical change. This change is reversible and does not involve formation of any new substances. The change is irreversible and is thus a chemical change.
Lighting of electric bulb - Glowing of a bulb is a physical change. When electric current is passed through the bulb, the filament starts glowing and the glow stops as soon as we stop the current. Here, the change is temporary ,no new products are formed and there is no chemical change in the tungsten of the filament.