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Measuring the Enthalpy of Combustion for Alcohols

Essay by   •  October 16, 2017  •  Lab Report  •  1,978 Words (8 Pages)  •  783 Views

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Laboratory Report: Measuring the Enthalpy of Combustion for Alcohols

Data Collection

Table 1: combustion of ethanol

Trial 1

Trial 2

Trial 3

Mass of spirit ([pic 1]

g ± 0.01

Temperature of the Water ([pic 2]

°C ± 0.5

Mass of spirit ([pic 3]

g ± 0.01

Temperature of the Water ([pic 4]

°C ± 0.5

Mass of spirit ([pic 5]

g ± 0.01

Temperature of the Water ([pic 6]

°C ± 0.5

Initial

339.16

21.0

336.96

21.0

334.45

22.5

Final

336.96

43.0

334.45

41.0

332.17

43.5

Volume of water = 100  ± 1[pic 7]

Table 2: combustion of butan-1-ol

Trial 1

Trial 2

Trial 3

Mass of spirit ([pic 8]

g ± 0.01

Temperature of the Water ([pic 9]

°C ± 0.5

Mass of spirit ([pic 10]

g ± 0.01

Temperature of the Water ([pic 11]

°C ± 0.5

Mass of spirit ([pic 12]

g ± 0.01

Temperature of the Water ([pic 13]

°C ± 0.5

Initial

309.14

23.5

307.27

24.0

304.97

21.5

Final

307.27

44.0

305.02

44.5

303.11

42.0

Volume of water = 100  ± 1[pic 14]

Table 3: combustion of pentan-1-ol

Trial 1

Trial 2

Trial 3

Mass of spirit ([pic 15]

g ± 0.01

Temperature of the Water ([pic 16]

°C ± 0.5

Mass of spirit ([pic 17]

g ± 0.01

Temperature of the Water ([pic 18]

°C ± 0.5

Mass of spirit ([pic 19]

g ± 0.01

Temperature of the Water ([pic 20]

°C ± 0.5

Initial

213.00

24.0

211.72

24.0

210.60

24.5

Final

211.72

44.0

210.60

44.0

209.09

44.5

Volume of water = 100  ± 1[pic 21]

Observations:

  • I always weighed the alcohols together with the beakers and the caps.
  • I changed the water after each trial but some of the water may have stayed in the beaker therefore meaning that the volume of water might have been slightly higher after the first trial with ethanol.
  • It always took some time to look at the temperature recorder by the thermometer meaning that the final temperatures might have been slightly higher.
  • I lit the alcohol before positioning it under the water: some of the mass may have been lost without any change in the temperature of the water.
  • The flames were never directly directed to the water beaker.
  • For all of the three alcohols, including the three trials for each, the raise in temperature was never constant.
  • Traces of carbon depositing on the bottom of the beaker only appeared during the combustion of pentan-1-ol.
  • The colors of the flame were different according to the alcohol which was undergoing combustion: • ethanol  the flame was partially blue and partially yellow.

• butan-1-ol  the flame was yellow-orange.

• pentan-1-ol  the flame was yellow-orange.


Data Analysis

Average change in the temperature of water ()[pic 22]

[pic 23]

[pic 24]

Uncertainty on  = The sum of the absolute uncertainties of the 6 temperatures used in order to calculate  divided by 3. Since the absolute uncertainties are are equal, the uncertainty on  will simply be equal to 2 * 0.5°C. Uncertainty on  = 2 * 0.5°C = ± 1.0°C.[pic 25][pic 26][pic 27][pic 28]

Average change in the temperature of water for ethanol

 °C ± 1.0[pic 29]

Average change in the temperature of water for butan-1-ol

 °C ± 1.0[pic 30]

Average change in the temperature of water for pentan-1-ol

 °C ± 1.0[pic 31]

Energy released by the alcohol during combustion (Q)

Energy released by the alcohol = - energy absorbed by the water

[pic 32]

We assume that 1 of water has a mass of 1g, therefore the mass of the water used for each trial ( = 100g ± 1[pic 33][pic 34]

c (specific heat capacity of water) = [pic 35]

c has no uncertainty

[pic 36]

% uncertainty on Q =  [pic 37]

[pic 38]

Energy released by ethanol during combustion

[pic 39]

Energy released by butan-1-ol during combustion

[pic 40]

Energy released by pentan-1-ol during combustion

[pic 41]

Average mass of alcohol combusted (m)

[pic 42]

[pic 43]

Uncertainty on  = The sum of the absolute uncertainties of the 6 masses of the spirits used to calculate , divided by 3. Since the 6 absolute uncertainties are equal, the uncertainty on  will be equal to 2* (the uncertainty on ). Uncertainty on  =.[pic 44][pic 45][pic 46][pic 47][pic 48][pic 49]

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