The aim of the investigation is to discover the relative amount of heat energy that a set of alcohols release during the combustion process. Then the energy discharged by one mole of that alcohol must be found. Basic terms: Exothermic reaction – In an exothermic reaction, the heat energy of the products is less than the heat energy of the reactants. As the reaction occurs, excess heat energy is released and so the energy change between the products and reactants is negative due to the heat being lost. The air near the fuel, rising in temperature, demonstrates this.
Endothermic reaction – In an endothermic reaction, the heat energy of the products is greater than that of the reactants. Heat energy is taken from the surroundings during the reaction and causes the energy change to be positive (heat energy is gained). Thus, the temperature of the air near the burning fuel falls. Specific Heat Capacity – This is defined as the quantity of energy that is required to raise the temperature of 1kg of a substance by 1 degree Celsius. Its units are J/kgi?? C. Heat content varies from compound to compound and depends on the physical state of the compound.
Here are the specific heat capacities of some other substances and a specific heat energy diagram: Homologous series – This is a term used to describe members of the same family, which have similar chemical properties and react in a similar fashion as you go down the group. For example, the alkanes group or even the alkali metals in group one. Structures of alcohols – Alcohols have an atomic structure similar to that of the homologous series alkanes – a carbon ‘backbone’ linked to hydrogen atoms. However, a single -OH group, has replaced one of these outer hydrogen atoms.
Strong covalent bonds connect the various atoms to each other although the forces between the alcohol particles are quite weak. This signifies that they have low melting and boiling points and can be easily separated from one another. Here is the structure of ethanol: Alcohols form their own distinct homologous series with these properties: solubility in water (smaller molecules can dissolve in water because of the OH group), higher boiling point than the alkanes (even though the weak intermolecular bonds mean that alcohol should have a very low boiling point, the addition of the OH group allows a higher one) and that they are flammable.
The basic formula for an alcohol is: CnH2n+1 where n is the number of carbons. Here is a table displaying the entire set of alcohols: Combustion – The reaction between a fuel and oxygen is known as combustion. The fuel reacts with oxygen gas in the air and gives out heat as a by-product. There are two types of combustion: Complete combustion of a fuel happens when there is plenty of oxygen and will produce carbon dioxide and water HYDROCARBON + OXYGEN = CARBON DIOXIDE + WATER. The Incomplete combustion of a fuel happens when there is not enough oxygen.
It is dangerous because it creates carbon monoxide and carbon as products HYDROCARBON + OXYGEN = CARBON MONOXIDE + CARBON. The basic reaction can be explained by use of the following scientific facts and theories: When the alcohol is lit in air, the heat energy from the surroundings is used to break the bonds of the alcohol and around the alcohol, those of the oxygen molecules. So the first part of the reaction is done in an endothermic fashion. The burning of a fuel in air is known as combustion. Combustion in terms of energy is the heat produced when one mole of a substance is completely burnt in oxygen.
Once the bonds of the two elements are broken, they then employ heat energy to create the new product bonds which will be: carbon dioxide and water (vapour). As stated before – From this, heat energy is lost/given to the air illustrating that this is an exothermic reaction (the energy difference between the reactants and the products determines the heat given out when the products are formed). Meanwhile, the air molecules around the reaction receive this excess heat energy, which causes them to vibrate faster and faster and makes them hotter and hotter.
The energy is passed from these particles to other ones (by ‘bumping’ into each other) and conducted along others until it eventually reaches the can of water. To raise the temperature of the water, energy must be given to it’s molecules to make them vibrate faster and produce heat in the same manner as air. So the heat energy is conducted through the metal atoms of the can and to the water molecules. After enough heat energy has been conveyed to the water so as to satisfy its energy needs, then the temperature will increase by a certain degree.
The many water molecules vibrating at a fast rate cause this. Independent Variable: The independent variable is the different alcohols that we are using. Dependent variable: The dependent variable is the amount of energy released when the alcohol is involved in combustion. The other important variables (the ones I must control) are: Distance between the spirit burner and the can Environmental factors such as wind and air temperature Volume of water in the can Other systems absorbing heat/ material of the can Heat being lost by evaporation Incomplete combustion occurring.
These variables are important in my investigation for the following scientific reasons: The distance between the spirit burner and the can is important as the greater the distance from the spirit burner, the more heat that will need to be produced in order for enough to reach the water. This implies that a larger mass of alcohol will be burnt. Heat travels through the air when they ‘bump’ into each other and this heat is generated by the combustion of the alcohol. If the distance between the two objects is increased, then the conduction of heat from the reaction to the can will take longer meaning:
Some particle heat energy will be lost to the surroundings along the way. The water will get less heat energy at the end of it all, indicating that it will take longer to raise its temperature. The longer the water takes to heat, the more the mass of the alcohol is lost through burning. So the alcohol will be involved in more combustion reactions (burning away its mass) if the distance is increased, in order to provide enough heat energy for the water to raise its temperature. Environmental factors may affect the alcohol’s distribution of heat energy by causing some to be lost to the surroundings.