Consider the following reaction: Fe2O3(s) + 2Al(s) → 2Fe(s) + Al2O3(s) Which of the following statements about the given reaction is NOT correct?
It is highly endothermic reaction
Understanding the Fe₂O₃ + Al Reaction
The given chemical reaction is:
\(\text{Fe}_2\text{O}_3(\text{s}) + 2\text{Al}(\text{s}) \rightarrow 2\text{Fe}(\text{s}) + \text{Al}_2\text{O}_3(\text{s})\)
This reaction involves solid iron(III) oxide (\(\text{Fe}_2\text{O}_3\)) reacting with solid aluminum (\(\text{Al}\)) to produce solid iron (\(\text{Fe}\)) and solid aluminum oxide (\(\text{Al}_2\text{O}_3\)). This specific reaction is widely known as the thermite reaction.
Analyzing the Type of Reaction: Displacement and Redox
In the thermite reaction, aluminum is more reactive than iron. Aluminum displaces iron from its oxide compound. Therefore, this reaction is an example of a displacement reaction.
Let's also look at the oxidation states:
- In \(\text{Fe}_2\text{O}_3\), the oxidation state of Fe is +3.
- In \(\text{Al}(\text{s})\), the oxidation state of Al is 0.
- In \(\text{Fe}(\text{s})\), the oxidation state of Fe is 0.
- In \(\text{Al}_2\text{O}_3\), the oxidation state of Al is +3.
Iron's oxidation state changes from +3 to 0 (gain of electrons), so iron is reduced. Aluminum's oxidation state changes from 0 to +3 (loss of electrons), so aluminum is oxidized.
Since both reduction and oxidation occur, this is also a redox reaction.
Identifying Oxidizing and Reducing Agents
- The substance that causes reduction (by being reduced itself) is the oxidizing agent. In this reaction, \(\text{Fe}_2\text{O}_3\) is reduced, so \(\text{Fe}_2\text{O}_3\) acts as the oxidizing agent.
- The substance that causes oxidation (by being oxidized itself) is the reducing agent. In this reaction, \(\text{Al}\) is oxidized, so \(\text{Al}\) acts as the reducing agent.
Energy Change: Exothermic or Endothermic?
The thermite reaction is famous for producing a large amount of heat. It releases a significant amount of energy into the surroundings. Reactions that release heat are called exothermic reactions.
An endothermic reaction, on the other hand, absorbs heat from the surroundings.
The thermite reaction is highly exothermic, not endothermic.
Applications of the Thermite Reaction
Because of the intense heat produced and the formation of molten iron, the thermite reaction has practical applications, most notably in thermite welding. This technique is used for joining metal parts, such as welding railway tracks.
Evaluating the Given Statements
Let's examine each statement provided in the options:
- Statement 1: It is an example of displacement reaction
As discussed, aluminum displaces iron from iron oxide. This is a displacement reaction. This statement is correct.
- Statement 2: It is highly endothermic reaction
The thermite reaction releases a large amount of heat; it is highly exothermic. This statement claims it is highly endothermic. This statement is incorrect.
- Statement 3: \(\text{Fe}_2\text{O}_3\) acts as oxidizing agent
In this reaction, \(\text{Fe}_2\text{O}_3\) causes the oxidation of aluminum and is itself reduced. Therefore, \(\text{Fe}_2\text{O}_3\) acts as the oxidizing agent. This statement is correct.
- Statement 4: This reaction is applicable to joining of railway tracks
The intense heat and molten iron produced are used in thermite welding, commonly for joining railway tracks. This statement is correct.
The question asks for the statement that is NOT correct. Based on our analysis, the statement claiming the reaction is highly endothermic is incorrect.
Revision Table: Summary of Thermite Reaction Properties
| Property | Description for Fe₂O₃ + Al Reaction |
|---|---|
| Reaction Type | Displacement, Redox Reaction |
| Energy Change | Highly Exothermic (releases heat) |
| Oxidizing Agent | Fe₂O₃ |
| Reducing Agent | Al |
| Applications | Thermite Welding (e.g., joining railway tracks) |
Additional Information: Why Aluminum is Used
Aluminum is used in the thermite reaction because it is a highly reactive metal and has a strong affinity for oxygen. When heated with metal oxides like \(\text{Fe}_2\text{O}_3\), aluminum readily reduces the metal oxide to the free metal and forms stable aluminum oxide (\(\text{Al}_2\text{O}_3\)), releasing a large amount of energy in the process.
The thermite mixture requires initiation by heating to a high temperature (often using a fuse containing magnesium ribbon or a mix of potassium permanganate and glycerine). Once initiated, the reaction proceeds very vigorously.
Important Questions from Chemical Reaction
- Which one of the following is not an example of a redox reaction?
- Which one of the following is not a pigment?
- Which one of the following reactions is an example of decomposition reaction?
Match List I with List II and select the correct answer using the code given below the Lists:
LIST I
(Chemical process)
LIST II
(Reaction)
A.
Electrolysis of water
1.
Double displacement
reactionB.
Burning of coal
2.
Combination reaction
C.
Iron nail immersed in copper sulphate solution
3.
Decomposition reaction
D.
Addition of barium chloride solution to aluminium sulphate solution
4.
Displacement reaction
Consider the following reaction:
2HgO \( \stackrel{\Delta}{\longrightarrow} \) 2Hg + O2
The respective state of HgO, Hg and O2 in the above reaction is
