New idea about latent heat

1. LATENT HEAT
Prepared by
MAHMOOD AMIN
MSc. Physics

2. 2
Last lesson?

3. 3
Change of State
Matter exists in 3 states
Solid Liquid Gas

4. 4
Thinking
What happens if we put ice with a temperature
of -25 C in a pan and then place the pan on a
hot burner?

5. 5
During a change of phase, the K.E of the
molecules stays the same, but the
average P.E changes.
Phase changes and P.E between particles?

6. 6
Phase change?
The physical
change of a
substance from one
state (solid, liquid,
or gas) to another.

7. 7

8. 8
What's HEAT?
Is the Q that is exchanged between 2 objects at different
temp. or between 2 objects at the same temperature
when one of them is undergoing a phase change.
 When heat is added to a substance, melting,
vaporization or sublimation may occur.
 When heat is extracted from a substance,
freezing, condensation, and deposition may
occur.

9. 9
At what temperature does the substance begin to
melt?
 What temperature does it boil?
 At which section is the substance a solid? liquid?
gas?
What sections of the graph have constant potential
energy?

10. 10
HEAT
Add Extract
Melting Vaporization
sublimation
Freezing
Condensation
Deposition

11. 11

12. Last lesson checking?
 What say to the physical change of a substance from one
state to another?
 From 0C ice to 0C water the potential energy will……………
a. Increase b. decrease c. stay same
 Changing from Gas to Solid…………..
a. Evaporation b. Solidification c. Deposition
 In the……… change molecules separate easily
a. Sublimation b. Solidification c. Deposition

13. 13
P.E & Phase changes?
P.E
If r  r◦

14. 14
Vibration of molecules( particles) increase in K.E.
Break the bonds between particles increase in P.E.

15. 15
Net E added to ice = P.E. broken - P.E. newly bond
If ice is melting the absorbed E is sufficient to
break the weak bonds.
Different bonds form between liquid water will be
form.

16. 16
Lf =
𝑸
𝒎
Lf from:
Solid Liquid
At constant:
 Temperature
 Pressure
 Melting
 Freezing

17. 17
Lv =
𝑸
𝒎
At constant:
 Temperature
 Pressure
Lv from:
Liquid Gas
 Vaporizing
 Condensing

18. 18
Net E + to a substance during vapo. = P.E. of
attraction between the particles of a liq. - P.E. of
attraction between the particles

19. Energy has to be
calculated for:
 Phase change
 No phase change

20. Phase change temp. is not changing
P.E increase or decrease
Q = mL
Heat(J)=mass(kg) latent heat(J/kg)
20

21. No phase change just temp. is changing
Q = m • Cp • ΔT
Heat(J)=mass(kg)specific heat (J / (kg . K))change in temp.
K.E. increase or decrease
21

22. 22
Gas
1
Liquid
1
Solid
1

23. 23
A 5kg mass of ammonia at its boiling point is vaporized
when 6.5MJ of heat is supplied to it. Calculate the Specific
Latent Heat of Vaporization of ammonia.

24. 24
Q. This formula is used to find the amount of heat
(energy) necessary when there's a phase change
Q= (h)(ΔT) Q=(m)(L) Q=(m)(c)(ΔT) Q=(k)(A)(dT)
Q. What letter represents boiling?
Q. Why does the graph have two flat
lines at "b" and "d"?

25. 25
Q1/Amount of energy required to change the liquid to gas and vice
versa without any change in temperature is termed as:
Heat capacity
Latent heat of vaporization
Latent heat of fusion
Specific heat capacity