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.
![**Electrochemical Cells and Reactions**
In this section, we will explore a question related to electrochemical cells and the behavior of copper (Cu) in a specific reaction.
**Question (3):**
"Cu is positive in this reaction. Explain why in this reaction?"
The reaction provided is:
\[ \text{Zn(s)} | \text{Zn}^{2+} || \text{Cu}^{2+} | \text{Cu} \]
In the diagram above, an electrochemical cell is represented, consisting of zinc (Zn) and copper (Cu) electrodes. The notation suggests that the cell involves a zinc electrode in solid form (Zn(s)) and a copper electrode in solid form (Cu), each immersed in their respective ionic solutions — zinc ions (\(\text{Zn}^{2+}\)) and copper ions (\(\text{Cu}^{2+}\)). The double vertical lines (||) in the cell notation represent the salt bridge or membrane separating the two half-cells.
The question hints at understanding why copper (Cu) is considered positive in this cell reaction and asks whether it gains electrons from \(\text{Cu}^{2+}\), which has a 2+ charge.
Here’s an explanation:
In an electrochemical cell, each half-cell reaction facilitates either oxidation or reduction. Typically, Zinc (Zn) undergoes oxidation (loses electrons), while Copper (Cu) undergoes reduction (gains electrons).
### Half-Reactions:
**Oxidation Half-Reaction (at anode):**
\[ \text{Zn(s)} → \text{Zn}^{2+} (aq) + 2e^- \]
**Reduction Half-Reaction (at cathode):**
\[ \text{Cu}^{2+} (aq) + 2e^- → \text{Cu(s)} \]
In this setup:
1. **Oxidation Occurs at Zinc Electrode (Anode):**
Zinc metal (Zn(s)) loses electrons (is oxidized) to form \(\text{Zn}^{2+}\) ions.
2. **Reduction Occurs at Copper Electrode (Cathode):**
Copper ions (\(\text{Cu}^{2+}\)) in the solution gain electrons (are reduced) to form copper metal (Cu).
As a result of these half-reactions, zinc acts as the anode (negative electrode), and copper acts as the cathode (positive electrode).](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F5106b7d5-4699-43ee-ae46-0af4e3f0b206%2F3e93cd8d-b573-420c-98c2-b1c241870b84%2Feosr0zb_processed.jpeg&w=3840&q=75)
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