Benzoic acid, C7H6O2, occurs naturally in many berries. Suppose you burn 1.500 g of the compound in a combustion calorimeter and find that the temperature of the calorimeter increases from 22.50 °C to 31.69 °C. The calorimeter contains 775 g of water, and the bomb has a heat capacity of 893 J/K. How much heat is evolved per mole of benzoic acid? b) Refer to problem 11 above. The balanced equation for the combustion of benzoic acid is 2 C7H6O2 (s) + 15 O2 (g) → 14 CO2 (g) + 6 H2O (l). Calculate ∆E and ∆H for the above reaction as written. Assume the reaction occurs at 31.69°C. ---------------------------------------------------------------------------------------------------------------------- Answer: a) - 3.09 × 10^3 kJ/mol b) ∆E = - 6.18 × 10^3 kJ w = + 2.534 kJ ∆H = - 6.18 × 10^3 kJ
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) Benzoic acid, C7H6O2, occurs naturally in many berries. Suppose you burn 1.500 g of
the compound in a combustion calorimeter and find that the temperature of the
calorimeter increases from 22.50 °C to 31.69 °C. The calorimeter contains 775 g of
water, and the bomb has a heat capacity of 893 J/K. How much heat is evolved per
mole of benzoic acid?
b) Refer to problem 11 above. The balanced equation for the combustion of benzoic
acid is
2 C7H6O2 (s) + 15 O2 (g) → 14 CO2 (g) + 6 H2O (l).
Calculate ∆E and ∆H for the above reaction as written. Assume the reaction occurs
at 31.69°C.
----------------------------------------------------------------------------------------------------------------------
Answer: a) - 3.09 × 10^3 kJ/mol b) ∆E = - 6.18 × 10^3 kJ w = + 2.534 kJ ∆H = - 6.18 × 10^3 kJ
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