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Planning Exercise 2: Energetics & Alcohols

The enthalpy change of combustion of ethanol, ∆Hc, can be determined experimentally under laboratory conditions using the following apparatus.

(a) Using the apparatus shown above and any other apparatus required that is normally found in a school laboratory, plan a step-by-step method to determine the enthalpy change of combustion of ethanol, ∆Hc. [4] 1. 2. 3. 4. 5. Measure 50.0 cm3 water with a measuring cylinder and fill into the copper can. Set up the appratus as shown. Measure and record the initial temperature of the water. Weigh and record the mass of the entire spirit lamp containing ethanol. Light up the spirit lamp. Stir the contents of the copper can until there is a appreciable increase of 5 °C rise in temperature. 6. Blow to extinguish the flame and record the final temperature in the table 7. Reweigh the entire spirit lamp.

Alternative method: Other than burning ethanol to get a particular temperature rise, you may instead burn a measured mass of ethanol completely OR burn ethanol for a particular length of time.

© 2011/H2 Chemistry 9647/JC2/Term1/Practical/Chem Dept


Planning Exercise 2: Energetics & Alcohols

(b) Show how you would tabulate your results. All necessary measurements should be shown in the table. You may use letters to represent each reading obtained e.g. T1, T2 to represent temperature readings, M1, M2 to represent mass readings etc. [1] Mass of spirit lamp + ethanol before combustion / g Mass of spirit lamp + ethanol after combustion / g Mass of ethanol burnt / g Initial temperature of water / oC Final temperature of water / oC Temperature rise of water / oC M1 M2 M1 – M2 T1 T2 T2 – T1

(c) Using the lettered symbols in your table, show how you would process your results to find the enthalpy change of combustion of ethanol, ∆Hc. [1] Heat evolved during combustion = heat gained by water in copper can = 50.0 x 4.18 x (T2 – T1) J Number of moles of ethanol burnt = (M1 –...
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