PAG 3.3 determination of enthalpy changes of combustion

Question 1

method

Answer 1

1) measure 100 cm3 of water into a beaker
2) weigh a spirit burner containing one of the alcohols
3) arrange the apparatus in a way where the spirit burner can heat the water
4) take the temperature of the water before you heat it
5) stop heating when the water has had a reasonable temperature rise >15 degrees
6) reweigh spirit burner
7) repeat with other alcohols

Question 2

suggest three reasons why there is a difference in the experimental value and the literature value of the enthalpy change

Answer 2

heat lost to the surroundings
incomplete combustion forming soot
evaporation of alcohol from the wick on the spirit burner

Question 3

suggest how the experiment could be improved to give more accurate results

Answer 3

use a draught excluder or a screen to reduce draughts
have the balance closer to you so you can weigh spirit-burner more accurately
stir constantly and don’t take lid off to stir
place experiment in a container with a constant flow of oxygen to stop incomplete combustion from happening