Comparing the Enthalpy Changes of Combustion of Different Alcohols
... ( C) ( C) (g) (g) Measure out 200cm of water and pour into the copper beaker. Record the temperature of the water. Support the calorimeter (using the clamp) over a spirit burner containing the alcohol you are going to burn Mark the position of the calorimeter in the clamp Arrange a suitable draft exclusion system (using the cardboard) to reduce heat loss. Weigh the spirit burner, containing the alcohol but without the lid. Record the measurement. Replace the burner under the calorimeter and light the wick When the water temperature has risen by between 15 and 20 C, extinguish the burner and record the highest temperature reached by the water. Weigh the burner again, without the lid and record the measurement. Empty out the calorimeter and wash it. Replace the copper calorimeter in the clamp at the marked position (i.e. the same position as before) and do the experiment twice more with the same alcohol so that you have three readings for the one alcohol. Now repeat the whole experiment with another burner containing a different alcohol. Keep all other conditions the same as the first alcohol. Use the same apparatus and the same mass of water. The only thing that should be different is the alcohol. Risk Assessment: This experiment can prove to be dangerous and hazardous. The alcohols do burn well and so can easily catch fire. To prevent this from happening, keep the surrounding area clear and make sure that there are no naked flames near the alcohols. Also, as alcohol vapours can catch fire the lid must remain on the spirit burner when not in use. The vapours of Ethanol and higher alcohols produce narcotic effects if inhaled; victims should be removed to fresh air. Also for self-protection goggles should be worn. However, if spilt in eyes, flood the eyes with running tap water for 10 minutes and then seek medical attention. Prediction; I am expecting that the alcohols with a greater number of carbon atoms within the molecule to have a higher enthalpy of combustion than the ones with less. This is because for any reaction to take place bonds must be broken and made, bond breaking requires energy while 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. I predict that as the number of carbon atoms in the carbon chain of the alcohol increases the reaction will become more exothermic and Hc will also become more exothermic. Also, I am expecting that the alcohols with the same molecular formula to have the same or very similar Hc values as they will have the same number of bonds to break and make. ANALYSIS Volume of water in calorimeter = 200cm3 Initial temperature of water = t1 C Final temperature of water = t2 C Initial mass of alcohol before burning = M1 g Final mass of alcohol after burning = M2 g Heat evolved by the combustion of alcohol = the heat gained by the water Heat evolved = Q = mc T J C = Specific heat capacity of water = 4.2J (*4.2J raises the temperature of 1g of water by 1 C) Heat evolved = mc T Kj 1000 Conclusion: 1) (a) Combustion Equations (i) Ethanol: C2H5OH C2H5OH + 3O2 = 2CO2 + 3H2O (ii) Propan-1-ol: C3H7OH C3H7OH + 4.5O2 = 3CO2 + 4H2O (iii) Butan-1-ol: C4H9OH C4H9OH + 6O2 = 4CO2 + 5H2O Hc of alcohols is exothermic. The reaction consists of bond breaking in the alcohol, which is endothermic and the formation of new bonds in CH2 and H2O, the combustion products. Since the overall reaction is exothermic, then the bonds made are stronger than the bonds broken. (b) Using data from a data sheet: ( Hc of butan-1-ol) – ( Hc of propan-1-ol) (-2676) _ (-2021) = (-655) ( Hc of propan-1-ol) – ( Hc of ethanol) (-2021) _ (-1367) = (-654) Looking at my calculated Hc values in the table above, which were calculated from my experiment the general pattern from these results is that as the number of carbon atoms increases the value of Hc becomes more exothermic . Propan-1-ol and propan-2-ol both have 3 carbon atoms and so the same number of bonds are made and broken during combustion so we would expect the value to be similar as sho...