Combustion Of Alcohols Essay Examples

Combustion Of Alcohols Essay

Combustion Of Alcohols

Planning

This investigation involves burning alcohol in the air. Key science- Chemistry by Eileen Ramsden says that " an alcohol is a series of organic, homologous compounds, with the general formula Cn H2n+1OH". The alcohol reacts with the oxygen in the air to form the products water and carbon dioxide:

Cn H2n+1OH +(n+n/2)-1O2 ? nH2O + nCO2

The structure of the molecules in this reaction is:

H H | | H - C - C - O- H + 3[O=O] ? 1/2[O=C=O] + 3[H-O-H] | | H H

This reaction is exothermic, as heat is given out. This is because the amount reactant energy is more than the product energy the difference between this is ?H, therefore some energy has been given out in the form of heat.The energy is given out when forming the bonds between the new water and carbon dioxide molecules. This can be shown in an energy level diagram: Reaction co-ordinate ?H is the heat content, which is the enthalpy, which is negative in exothermic reactions as the diagram shows that energy is 'lost' as heat. Enthalpy is defined as the energy of reaction, or the heat energy associated with a chemical change. Chemical Principles By Master & Slowinski says that "For any reaction carried out directly at a constant pressure, the heat flow is exactly equal to the difference between enthalpy of products and that of the reactants", or: Qp = Hp - Hr = ?H Where Qp is the heat flow at constant pressure, Hp is heat energy of products, and Hr is the heat energy of the reactants.

To measure ?H given off, we must use this energy to heat something, this will be water. This is assuming that all the heat produced by combustion of fuel (?H) will equal the amount of heat absorbed by the water (q). So I will measure the amount of energy required to do so. This can be worked out by useing the formula: q = mass X specific heat capacity X temperature rise 1000 Where q is the quantity of heat. The specific heat capacity is the amount of energy required to heat the substance, and is calculated using the formula q = MC?, where q is the enthalpy, is the specific heat capacity and ? is the temperature rise. I chose to use water as it is safe, easily obtainable, and has a constant, reliable specific heat capacity of 4.2J/?C.

The bonds which are made in a exothermic reaction "are forces of attraction between the atoms or ions in a substance" according to Key science- Chemistry by Eileen Ramsden. These can be of two types: covalent, in which the atoms share electrons. Examples of this are water and carbon dioxide, which has a double covalent bond because it shares two pairs of electrons are shared. The other type of bonds are ionic, where a metal is involved. This is where electrons are transferred from one ion to another, so there is an electrostatic force between the ions.

The variables that must be controlled are:

* Mass of water

* Amount of wick...

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EXAMPLE 1

(SPM 2012

– 

Paper3/Question 3)

Diagram 1 shows spirit lamps that contain different types of alcohols.Diagram 1Different types of alcohols produce different heat of combustions. When the number of carbon per molecule of the alcohol increases the heat of combustion increases.Table 1 shows the heat of combustion of ethanol, propanoland butanol.Table 1Plan an experiment to compare the heat combustion of thealcohols.Your planning should include the following aspects:

a.

 Aim:

To determine the heat of combustion of various alcohol 

[2 marks] 

b.

Statement of the problem

How does the number of carbon permolecule of alcohol affect the heat of combustion?

[2 marks]

c.

All the variables

Manipulated variable: Types of alcoholsResponding variable: Heat of combustionFixed variable: Volume of water, type of container, size of container and spirit lamp

[3 marks]

d.

Statement of the hypothesis

When the number of carbon per molecule of alcohol increases, the heat of combustionincreases.

[3 marks]

e.

List of substance/materials and apparatus

Substance/materialsEthanol, propanol, butanol, water, [metal]Apparatus

Copper container, spirit lamp, thermometer,electronic balance, wooden block, tripodstand, wind shield and measuring cylinder.

[3 marks]

f.

Procedure of the experiment

1.

250 cm

3

of water is poured into a coppercontainer as shown in the diagram above.2.

Initial temperature of the water isrecorded.3.

A spirit lamp is half filled with ethanol.4.

Initial mass of the spirit lamp is recorded.5.

The spirit lamp under the copper beakerand ignite the wick immediately.6.

Stir the water and the flame is put off after the temperature has increased by30°C.7.

The highest temperature of the water isrecorded8.

Immediately the final mass of the spiritlamp is recorded.9.

Repeat the experiment by replacingethanol with propanol and butanol.

[3 marks]

g.

Tabulating data

[3 marks]

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