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.
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![**Understanding Equilibrium Shifts in Chemical Reactions**
Consider the following reaction at equilibrium:
\[ N_2 (g) + 2H_2 (g) \rightleftharpoons N_2H_4 \quad \Delta H = -276 \, \text{kJ} \]
This reaction is exothermic as indicated by the negative enthalpy change (ΔH = -276 kJ).
**Predict the equilibrium shift (R- right, L - left, N - no change) in the following situations:**
1. **The reaction is put on ice**
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2. **N₂ is injected in the reactor**
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3. **N₂H₄ is injected in the reactor**
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4. **Helium is added and total pressure increased**
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5. **Catalyst is removed**
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6. **Reactor with a smaller volume is used**
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### Explanation
For each situation, consider Le Chatelier's Principle, which states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change.
1. **The reaction is put on ice:**
Cooling an exothermic reaction will shift the equilibrium to the right (towards products) to produce more heat, compensating for the decrease in temperature.
2. **N₂ is injected in the reactor:**
Adding more of a reactant like \( N_2 \) will shift the equilibrium to the right (towards products) to consume the added reactant.
3. **N₂H₄ is injected in the reactor:**
Adding more of a product, \( N_2H_4 \), will shift the equilibrium to the left (towards reactants) to consume the added product.
4. **Helium is added and total pressure increased:**
Helium is an inert gas and does not participate in the reaction. Adding an inert gas at constant volume does not affect the partial pressures of the reactants and products, hence equilibrium does not shift.
5. **Catalyst is removed:**
Removing a catalyst does not shift the equilibrium; it only affects the rate at which equilibrium is reached.
6. **Reactor with a smaller volume is used:**
Decreasing the volume increases the pressure. For reactions involving gases, the equilibrium](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F1b96ff29-61c4-4a18-af2c-3972ac9128c6%2Fbb96b25d-ea53-4fec-a516-5b358f3662af%2Fja7r139_processed.jpeg&w=3840&q=75)
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