A student runs two experiments with a constant-volume "bomb" calorimeter containing 1400.g of water (see sketch at right). First, a 6.500g tablet of benzoic acid C6H5CO2H is put into the "bomb" and burned completely in an excess of oxygen. (Benzoic acid is known to have a heat of combustion of /26.454kJg .) The temperature of the water is observed to rise from 11.00°C to 38.29°C over a time of 10.1 minutes. Next, 4.080g of ethane C2H6 are put into the "bomb" and similarly completely burned in an excess of oxygen. This time the temperature of the water rises from 11.00°C to 39.31°C . 2C2H6g + 7O2g -> 4CO2g + 6H2Og Be sure any of your answers that are calculated from measured data are rounded to the correct number of significant digits. Note for advanced students: it's possible the student did not do these experiments sufficiently carefully, and the values you calculate may not exactly match published values for this reaction. Is this reaction exothermic, endothermic, or neither? If you said the reaction was exothermic or endothermic, calculate the amount of heat that was released or absorbed by the reaction in the second experiment. Calculate the reaction enthalpy ΔHrxn per mole of C2H6
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.
A student runs two experiments with a constant-volume "bomb" calorimeter containing
of water (see sketch at right).
First, a
tablet of benzoic acid
is put into the "bomb" and burned completely in an excess of oxygen. (Benzoic acid is known to have a heat of combustion of
.) The temperature of the water is observed to rise from
to
over a time of
minutes.
Next,
of ethane
are put into the "bomb" and similarly completely burned in an excess of oxygen. This time the temperature of the water rises from
to
.
2C2H6g + 7O2g -> 4CO2g + 6H2Og
Be sure any of your answers that are calculated from measured data are rounded to the correct number of significant digits.
Note for advanced students: it's possible the student did not do these experiments sufficiently carefully, and the values you calculate may not exactly match published values for this reaction.
Is this reaction exothermic, endothermic, or neither?
If you said the reaction was exothermic or endothermic, calculate the amount of heat that was released or absorbed by the reaction in the second experiment.
Calculate the reaction enthalpy ΔHrxn per mole of C2H6.
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