A sample of solid biphenyl (C12H10) that weighs 0.4800 g is burned in an excess of oxygen to CO2(g) and H2O() in a constant-volume calorimeter at 25.00 °C. The temperature rise is observed to be 2.100°C. The heat capacity of the calorimeter and its contents is known to be 9.273×103 J K-1.(a) Write and balance the chemical equation for the combustion reaction. Use the lowest possible coefficients. Use the pull-down boxes to specify states such as (aq) or (s). If a box is not needed, leave it blank. Based on this experiment: (b) Assuming that ΔH° is approximately equal to ΔE, calculate the standard enthalpy change for the combustion of 1.000 mol of biphenyl to CO2(g) and H2O(). c) Calculate the standard enthalpy of formation per mole of biphenyl, using the following for the standard enthalpies of formation of CO2(g) and H2O().ΔHf° H2O () = -285.83 kJ mol-1 ; ΔHf° CO2(g) = -393.51 kJ mol-1
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 sample of solid biphenyl (C12H10) that weighs 0.4800 g is burned in an excess of oxygen to CO2(g) and H2O() in a constant-volume calorimeter at 25.00 °C. The temperature rise is observed to be 2.100°C. The heat capacity of the calorimeter and its contents is known to be 9.273×103 J K-1.
(a) Write and balance the chemical equation for the combustion reaction. Use the lowest possible coefficients. Use the pull-down boxes to specify states such as (aq) or (s). If a box is not needed, leave it blank.
Based on this experiment:
(b) Assuming that ΔH° is approximately equal to ΔE, calculate the standard enthalpy change for the combustion of 1.000 mol of biphenyl to CO2(g) and H2O().
c) Calculate the standard enthalpy of formation per mole of biphenyl, using the following for the standard enthalpies of formation of CO2(g) and H2O().
ΔHf° H2O () = -285.83 kJ mol-1 ; ΔHf° CO2(g) = -393.51 kJ mol-1
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