Describes an experiment to show the change in state on heating
Answers
In short :- Heat lost by hot body heat gained by cold body.
EXPLANATION :- When a hot and a cold object are placed in contact with each other in an isolated system.
1) Temperature of cold object increases due to gain of heat energy.
2) At the same time, temperature of hot object decreases due to loss of heat energy.
3) The process of heat exchange continues till both the object acquire the same temperature.
Experiment 1 :
(i) With the help of a thermometer, note the room temperature.
(ii) Take a few cubes of ice from refrigerator and put them in a container. Using a thermometer, note the temperature of the ice cubes.
(iii) Now allow the ice cubes be in the room temperature for a few minutes.
(iv) After a while you will notice that all the ice cubes has changed their state to liquid. Again, with the help of a thermometer, note the temperature of water.
(v) You will observe that the temperature of the water is higher than the temperature of the ice that you had noted earlier.
(vi) This proves that the state of ice changed to liquid when it absorbs heat from the atmosphere.
Experiment 2 :
(i) Take a candle and light it.
(ii) You will notice that the candle starts melting from the side of the candle.
(iii) This proves that the solid candle has changed its state to liquid wax upon heating.
Experiment 3 :
(i) Take about 100 ml of water in a steel vessel.
(ii) With the help of a thermometer, note the temperature of water.
(iii) Place the vessel on a burner and heat the water.
(iv) After a while the water in the vessel starts boiling and you can see water vapour from the surface of water.
(v) You can test the presence of water vapour in the air by covering the vessel with a sheet of newspaper. The paper gets wet.
(vi) With the help of a thermometer, again note the temperature of the boiling water.
(vii) The temperature of boiling water will be around 100 oC.
(viii) This proves that the state of water has changed from liquid to gas upon heating.