A 125 mg sample of benzoic acid, (Mr/g mol-¹ = 122.13), was burnt in a bomb calorimeter and an increase in temperature of 4.15 K was observed. AcH (C7H6O2,s) =-3227 kJ/mol, AcH(C5H12, 9) = -3537 kJ/mol at 298,15 K. Calculate i. The calorimeter constant. ii. The change in temperature upon combustion in the same bomb calorimeter of 125 mg pentane (Mr/g mol-¹ = 72.15) Express your answers in 5 significant figures.
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.
Mass of benzoic acid = 125 mg
Molar mass of benzoic acid = 122.13 g/mol
Temperature increase when 125 mg of benzoic acid is burnt = 4.15 K
Enthalpy of combustion of benzoic acid,
Mass of pentane = 125 mg
Molar mass of pentane = 72.15 g/mol
Enthalpy of combustion of pentane,
We have to determine the
- Calorimeter constant.
- Change in temperature when 125 mg pentane is burned in the same calorimeter.
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