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.
Steps for Lewis Structures:
1. Determine the total number of valence electrons. Add electrons for negative charges, subtract electrons for positive
charges.
2. Place least electronegative atom (except H) as central atom in structure.
3. Connect atoms by singles bonds. Each single bond = 2 electrons.
4. “Sprinkle” remaining electrons around outside atoms first to complete octets. Don’t use more electrons than the total found
in step 1. Then complete the central atom’s octet last if you have enough electrons.
5. Make double or triple bonds as needed to complete octets.
6. Place brackets and charge for ions.
For the central atom in each formula, draw the Lewis Structure with all valence electrons shown.
1. PH3
2. H2O
3. CO2
4. CHCl3
5. O2
6. N2
7. CF4
8. C3H8
9. CH3COOH
10. N2O
11. OCN-
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