Find the experimental molar enthalpy for each combustion reaction. b. Use the results from a) to calculate the enthalpy change associated with the target reaction (the cis/trans isomerism of 2-butene).
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
The following thermal data were collected during the combustion of cis-2-butene and trans-2-butene using a coffee can calorimeter (think of my marshmallow example). You may ignore the heat absorbed by the actual can itself and just use the water in your calculation. Use this information to calculate the heat of isomerization associated with the conversion from the cis to trans isomer.
|
Reaction I combustion of cis-but-2-ene |
Reaction II combustion of trans-but-2-ene |
|
|
mass of substance burned (g) |
0.022 g |
0.019 g |
volume of water in calorimeter |
100 mL |
100 mL |
|
initial temperature |
22.1 °C |
22.1°C |
|
final temperature |
24.6°C |
24.3°C |
a. Find the experimental molar enthalpy for each combustion reaction.
b. Use the results from a) to calculate the enthalpy change associated with the target reaction (the cis/trans isomerism of 2-butene).
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