Experiments (Heat and gases) Flashcards
(Latent Heat)
Cooling Curve of actadecan-1-ol
(Procedure)
Procedure (refer to textbook)
(1) Place some solid into a test tube.
(2) Heat the substance until all solid changes into liquid and about a few degrees above its melting point.
(3) Put a thermometer into the tube and immerse it into the liquid.
(4) Allow the tube to cool in air and record the temperature at 1-minute interval until a few degrees below the melting point.
(Latent Heat)
Cooling Curve of actadecan-1-ol
(Results + Conclusion)
RESULTS:
- when the liquid is cooled, heat is lost from the liquid throughout the cooling process.
- when the liquid reaches its melting point (freezing point), the liquid starts to change in solid.
- When liquid is changed into solid, temperature remains unchanged.
- When all the liquid has changed into solid, temperature falls again.
- Finally when the it reaches the room temp., the temperature stays constant.
CONCLUSION:
- The result shows that there is no temperature change during the change of state..
- When a substance is heated or cooled, either of the following happens (but not both) –> the temperature changes or the state changes
(Latent Heat)
Cooling Curve of actadecan-1-ol
(Analysis)
STAGE 1: LIQUID STATE
–> temperature decreases with decreasing rate because the temperature difference between the object and surrounding decreases. Heat loss decreases with time.
STAGE 2: LIQUID+SOLID STATE
–> Temperature remains unchanged because the heat loss equals to the decrease in potential energy in state. KE remains unchanged.
STAGE 3: SOLID STATE
–> Temperature decreases with decreasing rate because temperature with decreasing rate because the temperature difference between the object and surrounding decreases. Heat loss decreases over time.
(Latent heat)
Measure specific latent heat of fusion
Procedure:
(1) Put some crushed ice into a funnel placed above a beaker.
(2) A heater connected to a power supply via a joulemeter is put into the crushed ice. The energy E supplied by the heater is recorded by the joulemeter.
(3) Measure the mass m of water inside the beaker below the funnel.
(4) Specific latent heat of fusion of ice is found by E/m
Control experiment:
- the setup is identical to the experimental apparatus except that the heater is connected to the power supply –> same amount of crushed ice should be used in the two funnels.
- Find the mass of ice melt at room temperature, then the difference of the mass of ice melt is the mass of ice melt by heater
If not, the experimental value>true value
–>reason: initially, the mass of ice melt is overestimated
Crushed ice: increase surface area for better thermal contact with heater (reduce heat loss to surroundings)
Purpose of the control apparatus:
- to find out the amount of ice melted due to energy gained from the surroundings.
- to find out the actual amount of ice melted by the heater
(Latent heat)
Measure specific latent heat of fusion
–> Precautions
PRECAUTIONS:
1. The ice used be crushed to increase the surface area of the ice and ensure good thermal contact between the ice and the heater.
2. The ice should be melting to ensure that it is at the melting point
3. The heater should be inserted completely into the crushed ice.
(Latent heat)
Measure specific latent heat of fusion
–> Deviations
DEVIATIONS:
1. The ice used is not at its melting point but at a lower temperature.
- Extra energy is needed to raise the temperature of ice to its melting point
- The measured value would be greater than the actual value.
- There is heat gain from the surroundings
- The mass of ice melted would increase due to heat gained from surrounding air.
- The measured value would be smaller than the actual value. - There is heat lost to the surrounding air from the heater.
- More energy is supplied by the heater to heat the ice
- the measured value would be greater than the actual value
(Latent heat)
Measure Specific Latent heat of vaporisation of water
PROCEDURES:
A beaker containing water is placed on an electronic balance.
- A heater of known power P is immersed into the water.
- When the water boils, the reading of the balance is recorded.
- After a certain period of time t measured by a stopwatch, the reading of the balance is taken again. The difference of two balance readings gives the mass of water vaporised.
- The energy supplied by the heater E is found by E = Pt
- The specific latent heat of vaporization of water is then calculated by E/m.
(Latent heat)
Measure Specific Latent heat of vaporisation of wateR
–>PRECAUTIONS
PRECAUTIONS:
- 1. The heater should be completely immersed into the water.
- to reduce heat lost to the surrounding air: the beaker should be wrapped by insulating material and use a container made of insulating material such as a polystyrene cup.
3. the power of the heater should not be too large so that the boiling is not too vigorous to prevent water from splashing out of the beaker.
(Latent heat)
Measure Specific Latent heat of vaporisation of wateR
–>DEVIATIONS
DEVIATIONS:
1. Some energy is lost to the surrounding air
- more energy is supplied by the heater.
- the measured value would be greater than the actual value.
- Steam condenses at upper part of the apparatus and drains back to the beaker
- less steam escape from the beaker
- the measured value would be greater than the actual value - Boiling may be so vigorous that some water may splash out of the beaker
- more water would leave the beaker
- the measured value would be smaller than the actual value - The water has not reached its boiling point
- extra energy is needed to raise the temperature of water to its boiling point
- the measured value would be greater than the actual value
(Latent heat)
Measure Specific Latent heat of vaporisation of wateR
–>TWO POINTS TO NOTE
- No stirrer is needed
- during boiling, the temperature throughout the liquid remains constant. - The beaker must not be covered with lid
- If lid is covered, the steam cannot come out and the experiment does not work.
