Heat of combustion of Various Alcohols

Definition of heat of combustion, method to determine heat of combustion and compare heat of combustion between various alcohols

1. Heat of Combustion
Definition:
Heat given off when one mole of substanceis burnt
completely in an excess of oxygen.
Example:
C
3H
8+ 5O
23CO
2+ 4H
2O; = -2202 kJ mol
-1
Burning of 1 mol of propane in excess oxygen released
heat energy 2202 kJ
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2. To determine heat of combustion
of various alcohols
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3. To determine heat of combustion of
various alcohols
Alcohols
Measurement
MethanolEthanolPropan-1-olButan-1-ol
Initial mass of lamp(g)
Final mass of lamp(g)
Initial temperature of water(
o
C)
Final temperature of water(
o
C)
Heat given off by the alcohol
= heat absorbed b y the water
= mcθ
Number of moles of alcohol burnt
= mass of alcohol ÷molar mass
Heat given off when one mole of alcohol is burned
Heat of combustion of alcohol, ∆H
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4. Compare Heat of Combustion of
Various Alcohols
Alcohol Formula Molar mass Heat of combustion(kJ mol
-1
)
MethanolCH
3OH 32 -736
Ethanol C
2H
5OH 46 -1376
Propan-1-olC
3H
7OH 60 -2026
Butan-1-olC
4H
9OH 74 -2679
What is the relationship between number of
carbon atom per alcohol molecule and heat of
combustion?
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5. Heat of Combustion of Various
Alcohols
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