A sample of liquid phenol (C₆H₅OH (l), Mm = 94.12 g/mol) weighing 0.6749 g was burned in a bomb calorimeter at 25 °C, which caused a 1.543 °C rise in temperature. Calculate the enthalpy of combustion of phenol (in kJ/mol). You are using the same mass of both phenol and hexane. a. First we must calibrate the bomb calorimeter. A sample of hexane (C₆H₁₄ (l), Mm = 86.18 g/mol) was burned under identical conditions, causing an increase in temperature of 2.792 °C. Hexane has a heat of combustion under constant volume, ΔU = -4171.7 kJ/mol. What is the heat capacity of the calorimeter? b. Using the heat capacity you calculated in part a, calculate ΔU for the sample of phenol. c. Using the internal energy calculated in part b, calculate the enthalpy of combustion for phenol (in kJ/mol).
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 liquid phenol (C₆H₅OH (l), Mm = 94.12 g/mol) weighing 0.6749 g was burned in a bomb calorimeter at 25 °C, which caused a 1.543 °C rise in temperature. Calculate the enthalpy of combustion of phenol (in kJ/mol). You are using the same mass of both phenol and hexane.
a. First we must calibrate the bomb calorimeter. A sample of hexane (C₆H₁₄ (l), Mm = 86.18 g/mol) was burned under identical conditions, causing an increase in temperature of 2.792 °C. Hexane has a heat of combustion under constant volume, ΔU = -4171.7 kJ/mol. What is the heat capacity of the calorimeter?
b. Using the heat capacity you calculated in part a, calculate ΔU for the sample of phenol.
c. Using the internal energy calculated in part b, calculate the enthalpy of combustion for phenol (in kJ/mol).
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