Question A 1.(a) 6C(g) + 14H(g) CH14(g) H= -7510KJ/mol 7C(g) + 16H(g) C7H16(g) H= -7510KJ/mol Use the information given above to determine the average (C-C)and (C-H) bond energies Use the value obtained in (i) to calculate H for the following changes. 3C(g) + 8H(g) C3H8(g)
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.
Question A
1.(a) 6C(g) + 14H(g) CH14(g) H= -7510KJ/mol
- 7C(g) + 16H(g) C7H16(g) H= -7510KJ/mol
- Use the information given above to determine the average (C-C)and (C-H) bond energies
- Use the value obtained in (i) to calculate H for the following changes.
- 3C(g) + 8H(g) C3H8(g)
(b) You are given the following data of enthalpy of atomization of AI (KJ/mol).
Enthalpy of atomization of AI = +324
1st I.E of AI = +580
2nd I.E of AI = +1800
3rd I.E of AI = +2700
Enthalpy of atomization of Cl = +121
Estimated L.E of AlCl2 = -2602
L.E of AlCl3 = -5380
(i) Draw an energy level diagram for the following reaction
Al(s) + 3/2Cl(g) AlCl3(s)
(ii) Calculate the standard enthalpy of formation (Hf) of AlCl3
(iii) Why is AlCl3 formed in the reaction in (i) rather than AlCl2(s)?
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