Name: Depletion of Ozone Layer
Uploaded: 2019-07-19
Duration: 3 min 59 s
Description: The primary cause of ozone depletion and the ozone hole is manufactured chemicals, especially manufactured halocarbon refrigerants, solvents, propellants, an...

Question

The enthalpy of combustion of methanol can also be determined experimentally in a school laboratory. A burner containing methanol was weighed and used to heat water in a test tube as illustrated in figure.

The data shown in table were collected.

Initial mass of burner and methanol / $g$	$80.557$
Final mass of burner and methanol / $g$	$80.034$
Mass of water in test tube / $g$	$20.000$
Initial temperature of water / $° C$	$21.5$
Final temperature of water $° C$	$26.4$

The data booklet value for the enthalpy of combustion of methanol is $- 726 kJ {mol}^{- 1}$ . Suggest why this value differs from the values calculated experimentally.

Accepted Answer

Consider, the combustion reaction of methanol, ${CH}_{3} OH (l) + 1 \frac{1}{2} O_{2} (g) \overset{}{\to} {CO}_{2} (g) + 2 H_{2} O (g)$

The value of enthalpy of combustion of methanol determined by the given experimental data is found to be $- 25.153 kJ {mol}^{- 1}$ , and the data booklet value for the enthalpy of combustion of methanol is $- 726 kJ {mol}^{- 1}$ . Therefore, there is a difference in the values calculated from experimental data and the value of the data booklet. This is due to the fact that, during the reaction, not all heat produced transferred to water, heat lost to surroundings/environment. There may be also incomplete combustion of methanol, and the water forms as $H_{2} O (l)$ instead of $H_{2} O (g)$ as given in the thermochemical equation.

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