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Find the enthalpy change of combustion of a number of alcohol's' so that you can investigate how and why the enthalpy change is affected by the molecular structure of the alcohol.

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Introduction

Aim The aim is to find the enthalpy change of combustion of a number of alcohol's' so that you can investigate how and why the enthalpy change is affected by the molecular structure of the alcohol. Background Knowledge Combustion is principally the oxidation of carbon compounds by oxygen in air to form CO2 if there is a sufficient amount of oxygen. The hydrogen in a compound forms H2O. Combustion produces heat as well as carbon dioxide and water. The enthalpy change of combustion is the enthalpy change that occurs when 1 mole of a fuel is burned completely in oxygen. I can use an enthalpy cycle to work the combustion value out only if you have the right information. The energy contained in the bonds of the products is less than the energy contained in the bonds of the reactants. The difference in energy is released as heat. Energy releasing reactions are called exothermic reactions. Calorimetery is a way to determine the amount of heat produced in a reaction. Calorimeters are devices to measure heat released by a reaction. The temperature of the calorimeter increases as heat is released by the reaction. For any reaction to take place bonds must be broken and made Bond breaking requires energy whilst bond making releases energy. Bonds between different atoms require or release different amounts of energy when broken or made because they are different in strength. Chemical bonding is the electrical attraction between atoms or ions. When you break a bond you have to do work in order to overcome these attractive forces. To break the bond completely you need (theoretically) to separate the atoms or ions so they are an infinite distance apart. The quantity of energy needed to break a particular bond in a molecule is called the bond enthalpy. Breaking bonds is endothermic- needs energy. Making bonds energy is given out- exothermic. ...read more.

Middle

Seek medical attention. If split on skin or clothes: Remove contaminated clothing. Wash affected area thoroughly with cold water. Soak contaminated clothing to reduce fire risk if more than 10 ml. If spilt in laboratory: Shut off all sources of ignition. Open all windows and apply mineral absorbent to the spill. Scoop up into a bucket and add water. Store: As a Flammable liquid (FL). Handle it with care Heating- Wear eye protection. Never use an open flame to heat ethanol or methanol. If alcohol catches fire then cover with a heatproof mat to starve of oxygen. Propanol and Higher Alcohol's It is highly flammable, irritant and is harmful. Vapours may cause drowsiness or dizziness and maybe headaches. Irritating to the skin and harmful if swallowed. There is a risk of serious damage to the eyes. This alcohol's are irritant to the respiratory system. If swallowed: wash out mouth and give a glass or two of water. Seek medical attention. If vapour inhaled: Remove victim to fresh air to rest. Keep warm. If liquid splashed in eyes: Flood the eye with gently running tap water for 10 minutes. Seek medical attention. If split on skin or clothes: Remove contaminated clothing. Wash affected area thoroughly with cold water. Soak contaminated clothing to reduce fire risk if more than 10 ml. If spilt in laboratory: Shut off all sources of ignition. Open all windows. Cover with mineral absorbent and clear up into a bucket. Rinse area with a cloth. Wash the absorbent with dispersing agent and pour liquid down the foul-water drain. Store: As Flammable Liquids (FL). Handle it with care. Wear eye protection. The room should be well ventilated, but draughts may affect experimental work. Put alcohol's in spirit burners. The experiment can be shortened if smaller temperature changes are required and smaller volumes of water are heated. Goggles should be worn at all times. ...read more.

Conclusion

oxygen in the case of the combustion of fuel. The bomb is surrounded by water, which absorbs the heat from the reaction. The stirrer makes sure that the water is at constant temperature. All of this improves the accuracy of the enthalpy change of combustion values. Since the experiment is done in a closed container with a sealed vessel and lid and also done at constant volume means there is much less chance of heat escaping. Also the fact that an insulation chamber surrounds it means a less chance of heat escaping. This means my results will be more accurate and reliable. A Diagram showing a Bomb Calorimeter Another way to reduce heat loss is by using an insulation chamber to minimise heat loss. Insulation is a good way of minimising heat loss. I can silver the sides of the calorimeter to minimise heat loss by radiation, insulate the sides of the calorimeter and the insulation chamber to minimise heat loss by conduction and convection. This will ensure that the end enthalpy change of combustion value will be very accurate. To improve the experiment to achieve more accurate results I can choose to use the distilled water as opposed to tap water because tap water contains a variety of minerals and ions and the concentration of these may vary in view of repetition of the experiment also impurities in the water (may change the specific heat capacity of the water). This particular precaution is in aid of maintaining a fair experiment and limiting the inaccuracy of the experiment. To improve the accuracy and reliability of my results even further I could repeat the experiment a greater number of times. I would do the experiment six times for each alcohol and use a wider range of alcohol's e.g. I could use alcohol's up to hexan-1-ol instead of butan-1-ol. This would improve the accuracy and reliability of my results. A major way of improving the experiment is to do everything under standard conditions, which is 1 atmosphere pressure and 298K. This would produce the best results, which were the most accurate and reliable. ...read more.

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