1. 4.3
SPECIFIC LATENT HEAT

2. SPECIFIC HEAT CAPACITY
TEMPERATURE
THERMA EQUILIBRIUM
LATENT HEAT
SPECIFIC HEAT CAPACITY
SOLID
LIQUIDS
GAS

3. What is latent heat ?
Latent heat is defined as the heat absorbed or released when a substance changes its physical state completely at constant temperature

4. 2 different type of latent heat
Latent heat fusion
Latent heat of vaporization

5. What is latent heat of fusion ?
Latent heat fusion is the heat absorbed when a solid melt at constant temperature

6. During melting, the heat absorbed is used to break up the bonds between the particles. The particles are free from their fixed positions and are able to vibrate and move among each other .

7. What is latent heat of vaporization ?
Latent heat of vaporization is the heat absorbed when a liquid changes into vapor at constant temperature

8. When liquid boils, the heat absorbed is used to completely break the bonds of the particles and also to do work against atmospheric pressure when the gaseous vapor expands into the atmosphere.

9. LIQUID AND GAS GAS SOLID LIQUID SOLID AND LIQUID
The liquid starts to boil
Latent heat of vaporization is absorbed the liquid.
Molecules are held together tightly.
When heated, it gain energy and vibrate about their fixed position at greater speeds and amplitudes.
GAS
The liquid vaporizes completely into gas.
SOLID
LIQUID
The liquid temperature rises.
Molecules begin to moves faster and randomly.
The solid begin to melt.
Latent heat of fusion is absorbed by the solid.
The molecules are freed from their fixed positions and are able to move about.
SOLID AND LIQUID

10. What is specific latent heat?
Specific latent heat, L, of a substance defined as the amount of heat required to changed the phase of 1 kg of the substance at a constant temperature.
It can be calculated as;
L = Q/m

11. where;
Q = latent heat absorbed or released by the substance
m = mass of the substance
The S.I unit joule per kilogram (JKg-1)
The amount of heat required to change the phase of substance depends on the mass and type of material of the substance

12. Specific latent heat of fusion Specific latent heat of vaporization
Substance
Specific latent heat of fusion ºC
Specific latent heat of vaporization
kJ.kg-1
Water
334
2258
100
Ethanol
109
-114
838 78
Ethanoic acid
192 17
395
118
Chloroform 74
-64
254 62
Mercury 11
-39
294
357
Sulphur 54
115
1406
445
Hydrogen 60
-259
449
-253
Oxygen 14
-219
213
-183
Nitrogen 25
-210
199
-196

13. What is specific latent heat of fusion ?
Specific latent heat of fusion of a substance defined as the amount of heat required to change 1 Kg of the amount from solid to liquid phase at constant temperature

14. What is specific latent heat of vaporization ?
Specific latent heat of vaporization of a substance is defined as the amount of heat required to change 1 Kg of the substance from the liquid to gaseous phase without a change in temperature.

15. The S.I unit is joule per kilogram (JKg-1)
Heat needed to change one phase to another phase ;
Q = mL
If the heat is supplied by immersion electric heater;
Q = Pt
Where P = power
t = time
Pt = mL

16. EXAMPLES
The specific latent heat of fusion of ice is J/kg. What is the quantity of heat required to melt 1.5 kg of ice at 0oC.
Solution
Heat required, Q
= ml
=1.5 x
= 504 KJ

17. A 500 W electric heater is used to boil water
A 500 W electric heater is used to boil water. What is the time required to reduce the mass of water by 80 g after the water has reached its boiling point?
( Specific latent heat of vaporization of water
= 2.26 x 106 J/Kg)
Solution
Use the energy equivalence method.
Electric energy = Heat energy
Pt = mL
t = mL / P
= 0.08 x 2.26 x 106/ 500
= 362 s

18. CONCLUSION

19. LATENT HEAT 3 STATES OF MATTER CHANGE IN STATE SOLID LIQUIDS GASES
LATEN HEAT
OF FUSION
CHANGE IN STATE
LATENT HEAT OF
VAPORIZATION
LATENT HEAT IS ABSORBED
LATENT HEAT IS ABSORBED
SYMBOL: L
SI UNIT
JOULE/KG
SOLID LIQUID
LIQUID GAS
LATENT HEAT IS RELEASED
LATENT HEAT IS RELEASED
Q=ML
Q=Pt
ML=Pt