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Copy of Understanding specific latent heat

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by

Tara Kirk

on 27 September 2013

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Transcript of Copy of Understanding specific latent heat

Learning outcomes:
State that transfer of heat during a change of phase does not cause a change in temperature
Define specific latent heat
State that l=Q/m
Determine the specific latent heat of fusion
Determine the specific latent heat of vaporization
Solve problems involving specific latent heat

Goal
State that transfer of heat during a change of phase does not cause a change in temperature
Define specific latent heat
State that l=Q/m
Determine the specific latent heat of fusion
Determine the specific latent heat of vaporisation
Solve problems involving specific latent heat

during
Fusion
Vaporisation
Q=ml
Change of state
Observation
:
The ice is melting
Inference
:
There is a change phase from solid to liquid
The idea of change of phase
Inference
:
Observation
:
Temperature remains constant
Inference
:
The heat absorbed does not cause an increase
in temperature. The energy absorbed is not
transferred to the molecules as kinetic
energy.

Observation
The ice is colder than the surroundings
Inference
:
Heat energy is continuously being transferred from the surroundings to the ice
Conclusion
:

When the ice melts, it absorbed
heat without a change in its
temperature
Conclusion
:
When the ice melts, it absorbs
heat without a change in
its temperature
When a substance undergoes a change of phase such as melting or boiling, it absorbs heat without an increase in its temperature.
Latent heat
Processes and latent heat involved
Solid to liquid
Heat is absorbed
+
liquid to gas
boiling
Heat is absorbed
Gas to liquid
condensation
Heat is released
Freezing
liquid to solid
heat is released
latent heat fusion
latent heat is absorbed to weaken bonds between particles
Melting process
Particles vibrate about
their fixed mean position
The particles are freed from their position, vibrate and moves among each other
Latent heat vaporisation
When liquid are boils, latent heat absorbed is used to:
-completely break the bonds between the particles
Heat absorbed during boiling=latent heat
The amount of heat required to change the phase depend:
-mass
-type of substance
Mass
vs
Type
vs
Which one required more heat to melt?
Which one required more heat to melt?
specific latent heat
The amount of heat required to change the phase of 1kg of the substance at constant temperature
if heat is supplied electrically by a heater to change the phase of a substance:

Pt=ml
l=Q/m
Q=ml

Unit=Jkg^-1
Specific latent heat of fusion
The amount of heat required to change 1kg of the substances from solid to liquid phase without a change in temperature
Specific latent heat vaporisation
The amount of heat required to change 1kg of the substances from the liquid to gas without a change in temperature
Conclusion:
when ice melts, it absorbs heat without a change in its temperature
Can you identify the three phases of matter in this picture?
Phase changes require heat energy to be transferred into and out of a substances
4.3 Latent
heat
latent heat
Full transcript