This document discusses thermochmistry concepts including: 1) Exothermic reactions that release heat to the surroundings as reactants lose energy to form products with lower energy content and a negative ΔH. 2) Procedures for determining heat of combustion through burning an alcohol in excess oxygen and measuring the temperature change of surrounding water. 3) Key relationships like heat of reaction being the heat released or absorbed when 1 mole of products are formed and heat of combustion increasing with more carbon atoms and bonds in the molecule.

1. Rossita Radzak SASER
THERMOCHEMISTRY
1. Exothermic
– A chemical reaction that gives out heat to the surroundings
- The reactants lose heat energy to form the products
- The energy content of reactants is higher than products
- ΔH negative
2. Energy level diagram (label energy, reactants and product with correct chemical / ionic
formula, heat of reaction with unit.
3. Heat of reaction – heat change/releases when 1 mole of product formed. [ kJmol- ]
= mCǾ / mole
4. Heat of neutralization – heat releases when 1 mole of H+ combines with 1 mol of OH- to
form 1mole of water. H+ + OH-  H2O
5. Heat of combustion – heat releases when 1 mole of alcohol burnt completely in excess
oxygen.
C2H5OH + 3O2  2CO2 + 3H2O
6. As the number of carbon atom per molecule increases, the heat of combustion increases, due
to more products formed (CO2 & H2O) . Therefore more heat released when more bonds are
formed.
7. To determine heat of combustion (material and apparatus, procedure, tabulation of data,
calculation, observations, precautions)
Procedure:
1. (100 – 200) cm3 of water is measured using a measuring cylinder
2. and poured into a copper tin.
3. The initial temperature of water is measured and recorded, θ 1
4. A spirit lamp is filled with butanol/ other alcohol and weighed, x gram
5.The spirit lamp is light and put under the copper can.
6.The water is stirred continuously with a thermometer.
7.When the temperature of water increased by 30oC, the flame is put off.
8.The spirit lamp is weighed again, y gram
9.The highest temperature is recorded, θ2
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2. Rossita Radzak SASER
Results:
Mass of weight of spirit lamp + butanol /g x
Final mass of spirit lamp + butanol /g y
Mass of butanol used/g (x-y) // z
Highest temperature of water /oC θ1
Initial temperature of water /oC θ2
Increased in temperature /oC (θ1 - θ2 ) // θ3
Calculation:
Heat change = mcθ
= 100 x 4.2 x (θ2 – θ1)
=aJ
Heat of combustion of butanol = a J
(z/74 ) mol
Precautions :
1. Make sure the flame from the combustion of ethanol touches the bottom of the copper
can // The spirit lamp is placed very close or just beneath the bottom of the copper can.
2. Stir the water in the copper can continuously.
3. The spirit lamp must be weighed immediately (because the ethanol is very volatile).
4. A wind shield must be used during experiment.
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