(10.8)Which of the following resonance forms of SCN contributes least to its correct structure? (Hint: Assign the form charge for each atom in all resonance structures.) Ob O a Oa and b Oc [:$C=N:] (a) [S=C=N]¯¯ (b) [:S=C_N:] (c)
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:**
(10.8) Which of the following resonance forms of SCN⁻ contributes least to its correct structure? (Hint: Assign the formal charge for each atom in all resonance structures.)
**Resonance Structures:**
(a) \[ \text{[:S-C≡N:]}^- \]
(b) \[ \text{[:S=C=N:]}^- \]
(c) \[ \text{[:S≡C-N:]}^- \]
**Answer Options:**
- \( \circ \) b
- \( \circ \) a
- \( \circ \) a and b
- \( \circ \) c
**Explanation:**
To determine which resonance form contributes least to the correct structure of SCN⁻, it is beneficial to evaluate the formal charges assigned to each atom in the resonance structures.
**Formal Charge Calculation:**
- Formal Charge (FC) = [Valence electrons of the atom] - [Non-bonding electrons + 0.5(Bonding electrons)]
For each resonance structure:
(a) \[ \text{[:S-C≡N:]}^- \]
- S (Sulfur): FC = 6 - [6 + 0.5(2)] = 6 - [7] = -1
- C (Carbon): FC = 4 - [0 + 0.5(8)] = 4 - [4] = 0
- N (Nitrogen): FC = 5 - [2 + 0.5(6)] = 5 - [5] = 0
(b) \[ \text{[:S=C=N:]}^- \]
- S (Sulfur): FC = 6 - [4 + 0.5(4)] = 6 - [6] = 0
- C (Carbon): FC = 4 - [0 + 0.5(8)] = 4 - [4] = 0
- N (Nitrogen): FC = 5 - [0 + 0.5(8)] = 5 - [4] = +1
(c) \[ \text{[:S≡C-N:]}^- \]
- S (Sulfur): FC = 6 - [2 + 0.5(6)] = 6 - [5] = +1
- C (Carbon](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F8ace3a86-4905-4025-b5a4-d5dbea0f3d2b%2F28538fc9-db90-4d3e-ac73-2beb09342997%2Flzl3auc_processed.jpeg&w=3840&q=75)
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