Alcohols and Energy it takes to break them Essays

  Alcohols and Energy it takes to break them Essays   Alcohols and Energy it takes to break them Essay Alcohols and Energy it takes to break them Essay This experiment is to investigate how much energy alcohols give off when they are burnt. When burnt the alcohol reacts with oxygen to give the products Carbon Dioxide and Water. Chemical Formula: Structural formula (methanol) Structural formula (ethanol) The structural formulas for the rest of the group of the homologous alcohols have the same structure, with more carbon and hydrogen atoms arranged in the same way. In an exothermic reaction heat is given out when the new bonds are formed. When bonds are broken the heat energy is taken in so the reaction is endothermic. In this experiment we have an exothermic reaction because it produces more energy forming new bonds than breaking them. So it gives out heat energy. The energy output is found by subtracting the energy produced to form the bonds from the energy produced to break the bonds. This is known as the enthalpy, which is always negative as heat is lost from the reaction. This can be shown in this rough energy level diagram. Chemical Principles By Master Slowinski suggest that heat used by products (Hp) subtracted by heat used for reactants (Hr) equals the enthalpy (? H). It can be shown in this chemical formula. Hp Hr = ?H However doing a practical experiment is not the only way to work out the enthalpy of an alcohol. We can show it in energy level equations, using figures from textbooks to tell us the energy in kJ/mol. This is a good way to predict what results we might get from our experiments if they go according to plan. Here is an energy level equation, how to work out the energy produced by burning Methanol. Chemical symbol of bond Energy required to break/form bonds C-C 347 O=O 498 O-H 464 C=O 805 C-O 350 C-H 415 In our practical experiment to work out the amount of energy released from the reaction we need to use this equation. Heat Energy = mass of water x specific heat capacity x change in temperature = ________ Joules This equation is only assuming that the energy released by the alcohol we are burning is the same as the heat energy absorbed by the water. The specific heat capacity is the amount of energy required to heat the substance. The specific heat capacity of water is 4.2J/à ¯Ã‚ ¿Ã‚ ½C because that is the reliable figure that I have researched The bonds are made due to the forces of attraction between the atoms. This can be either covalent bonding, where the atoms share an electron, or ionic bonding which involves a metal and the one atom gives an electron to another atom. In our experiment the Hà ¯Ã‚ ¿Ã‚ ½O and the COà ¯Ã‚ ¿Ã‚ ½ are examples of covalent bonding. I need to make my experiment a fair test by keeping the material of container, the volume of water in the container, the change in temperature and the height of the container from the flame the same. The only variable I will not be changing is the type of alcohol and the time taken to burn it. The variables for this experiment are: Material of Container: The beaker I keep the water in has to be the same as some materials are better conductors of heat than others. I will probably be using a copper container as it is easy to find and can withstand high temperature. The material will heat up, and I will have to use wooden tongs to keep the experiment safe and make sure that I dont get burnt. Volume of Water in Beaker: This needs to be the same throughout all of my experiments otherwise heat will be lost in the environment quicker or slower than the previous experiment. I have chosen water because it is safe and easy to obtain. Change in Temperature: We will keep this the same so that each of the alcohols can release the same amount of energy. If we were to use time as our controlling factor, then a fast burning alcohol such as Pentanol would increase the temperature far quicker than a slower burning alcohol such as Methanol. Height of Beaker above flame: This should be kept the same so that not very much heat energy can escape from going into the water. A boss and clamp, or a tripod should control this; I will investigate in my preliminary work, which one will work better. Length of Wick: I dont have any control over this factor, other than the Burner that I am using, the wicks should all be about the same size anyway. However I will try and chose burners that have wicks roughly the same length. Preliminary Work: In my preliminary work I will be trying to find out what volume of water would be best to use and whether to use a tripod or a boss and clamp to hold the beaker in place. I will also be investigating the temperature change in the water and what mass of the alcohols I should be using. I need to decide how many alcohols to burn and also to see how far above the flame the beaker will need to be. I will also be investigating the material of the beaker that the water is held in and looking at the length of wick. Prediction of Diagram of Preliminary work: Results of Preliminary Work: I tried out two different volumes of water, 50ml and 100ml. 50ml of water reached the temperature very quickly and 100ml of water is easy to use in my enthalpy calculations. The length of wick couldnt be altered from the length that it was originally at. The distance of the wick from the bottom of the beaker could be altered easily. I started off with it at 6cm from the bottom of the container, but changed it to 4.5cm as the movement of air in the classroom tended to blow the flame about a lot. I decided to use a copper beaker instead of a glass one as copper transfers heat quickly and not a lot of heat will be used to heat the copper beaker up. I also discovered that I would have to use a boss and clamp instead of a tripod as a boss and clamp is a lot more stable and I can alter the height of the beaker more easily. I cannot alter the mass of the alcohol that I am using, but I can measure the mass before I start and the mass at the end of the experiment, to work out how much mass of the alcohol has been burned. To decide what the temperature change had to be I could work out what it couldnt be before my preliminary experiment. I could cool the water, but it would take up valuable practical time. I could change the starting temp of my water, but there was no point as it was 24à ¯Ã‚ ¿Ã‚ ½C, room temperature. I also couldnt raise it to more than 70à ¯Ã‚ ¿Ã‚ ½C incase some of the water evaporated. In the end I settled with 20à ¯Ã‚ ¿Ã‚ ½C temperature change as it didnt get too hot, and didnt take up too much time, so it allowed for some repeats. I also had to stir the water with a thermometer, to keep the heat constant in the copper container. Here are my preliminary results: Experiment 1: Mass changed from 127.22g to 126.7g when we burned Pentanol. We used 100ml of water and we had the beaker 6cm above the wick. The starting temperature was 24à ¯Ã‚ ¿Ã‚ ½C which we raised 10à ¯Ã‚ ¿Ã‚ ½C. Experiment 2: Mass changed from 126.7g to 126.0g when we burned Pentanol. We used 100ml of water and the beaker was 4.5cm above the wick. The starting temperature was 24à ¯Ã‚ ¿Ã‚ ½C, which we increased by 20à ¯Ã‚ ¿Ã‚ ½C. Experiment 3: Mass changed from 117.42g to 116.85g when we burned Methanol. We used 50ml of water and the beaker was 4.5cm above the wick. The starting temperature was 24à ¯Ã‚ ¿Ã‚ ½C and we raised it by 20à ¯Ã‚ ¿Ã‚ ½C. Experiment 4: Mass changed from 116.85g to 115.94g when we burned Methanol. We used 100ml of water and the beaker was 4.5cm above the wick. The starting temperature was 24à ¯Ã‚ ¿Ã‚ ½C and we raised it by 20à ¯Ã‚ ¿Ã‚ ½C. Diagram of Experiment: Apparatus: 1 measuring cylinder 5 different alcohol burners 1 copper container 1 box of matches 1 boss and clamp stand 1 pair of wooden tongs 1 thermometer 1 heat proof mat 1 set of scales A piece of paper and a pen 1 tap supplied with water Measurements: 100ml of water Copper Beaker 4.5cm above the burner I will be using a boss and clamp stand I will be raising the temperature of the water 20à ¯Ã‚ ¿Ã‚ ½C Method: 1) Measure 100ml of water into a copper container, making sure that the container is clean. If it is not clean then rinse it out before beginning experiment. 2) Record the mass of the alcohol burner and place on a heatproof mat next to the boss and clamp stand. 3) Set up the boss and clamp with the container 4.5cm above the wick of the burner. 4) Stir and record initial temperature of the water. 5) Light the wick immediately after I have done this and continue stirring the water. 6) As soon as the water has reached 20à ¯Ã‚ ¿Ã‚ ½C above the starting temperature blow out the wick and record the mass of the alcohol and burner. Throughout the test I will control the mass of water, 100ml, the same copper can and the wick 4.5cm from the bottom of the copper container. Predictions: I predict that alcohols with more carbon atoms in their chemical structure will produce more energy when their new bonds are formed. I predict that the alcohols with more carbon atoms such as Pentanol will produce more energy than an alcohol with less carbon atoms such as methanol. I also predict that the alcohols with more carbon atoms in their chemical structure will not have as much mass burned. This is because they are releasing more energy per gram than the alcohols with less carbon atoms in their chemical structure. Using the theoretical energy level diagram I can see how my results will come up against the theoretical ones. Alcohol Theoretical Energy Level Diagrams Results Methanol 666 kJ/mol Ethanol 1276 kJ/mol Propanol 1895 kJ/mol Butanol 2520 kJ/mol Pentanol 3138 kJ/mol Robert Bennett 10JR, 10A5 Robert Bennett 10A5 Dame Alice Owens School