describe an experiment to demonstrate that water absorbs heat during boiling at a constant temperature
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Apparatus :
A thermometer that can reach 100°C or 212°F.
Time or watch.
A round - bottomed flask held by clamps on a stand.
A Bunsen burner.
250ml of water or any amount as desired depending on the capacity of the round bottomed flask.
PROCEDURE
1. Put 250ml of water in the round bottomed flask and fit the top with a thermometer.
2. Light the Bunsen burner and pit it underneath the flask.
3. Take the temperatures of the water after every minute until boiling at 100°C.
4. After the water boils, take the temperature of the water five times after every minute.
5. Plot a graph of this to see the shape of the graph.
OBSERVATIONS
The water boils at a constant temperature which is 100°C
The graph of Temperature against time shows a curve that is rising until 100°C where it becomes flat.
EXPLANATIONS
As the water is boiling the water is changing from liquid to gas and this involves breaking of bonds between water molecules. This takes energy which is supplied in form of heat energy transferred to the water through conduction and convection. This energy is used to break the bonds between the water molecules and thus change the state from water to gas. The heat energy thus does not change the temperature but rather the energy of the molecules. Hence the boiling takes place at a constant temperature.
A thermometer that can reach 100°C or 212°F.
Time or watch.
A round - bottomed flask held by clamps on a stand.
A Bunsen burner.
250ml of water or any amount as desired depending on the capacity of the round bottomed flask.
PROCEDURE
1. Put 250ml of water in the round bottomed flask and fit the top with a thermometer.
2. Light the Bunsen burner and pit it underneath the flask.
3. Take the temperatures of the water after every minute until boiling at 100°C.
4. After the water boils, take the temperature of the water five times after every minute.
5. Plot a graph of this to see the shape of the graph.
OBSERVATIONS
The water boils at a constant temperature which is 100°C
The graph of Temperature against time shows a curve that is rising until 100°C where it becomes flat.
EXPLANATIONS
As the water is boiling the water is changing from liquid to gas and this involves breaking of bonds between water molecules. This takes energy which is supplied in form of heat energy transferred to the water through conduction and convection. This energy is used to break the bonds between the water molecules and thus change the state from water to gas. The heat energy thus does not change the temperature but rather the energy of the molecules. Hence the boiling takes place at a constant temperature.
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