2AgCI(s) \(\rm \xrightarrow{Sunlight} \) 2Ag(s) + CI 2(g)
Let's analyze the given reactions to identify which one is a decomposition reaction. A decomposition reaction is a type of chemical reaction where a single compound breaks down into two or more simpler substances.
Analyzing Chemical Reactions to Find Decomposition
We will examine each option provided and determine the type of chemical reaction it represents.
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$\text{CH}_4 \text{ (g) + 2O}_2\text{(g)} \rightarrow \text{CO}_2\text{ (g) + 2H}_2\text{O(g)}$
This reaction involves a substance (methane, $\text{CH}_4$) reacting rapidly with oxygen ($\text{O}_2$), producing heat and light. This is a typical example of a combustion reaction.
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$\text{2AgCl(s)} \rm \xrightarrow{Sunlight} \text{2Ag(s) + Cl}_2\text{(g)}$
In this reaction, a single compound (silver chloride, $\text{AgCl}$) breaks down into two simpler substances (silver, $\text{Ag}$, and chlorine gas, $\text{Cl}_2$) upon exposure to sunlight. This matches the definition of a decomposition reaction. Specifically, this is an example of photolytic decomposition, where decomposition is caused by light energy.
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$\text{CuO + H}_2 \rm \xrightarrow{Heat} \text{Cu + H}_2\text{O}$
Here, hydrogen ($\text{H}_2$) reacts with copper(II) oxide ($\text{CuO}$). Hydrogen removes oxygen from copper(II) oxide, reducing $\text{CuO}$ to $\text{Cu}$. Hydrogen itself gains oxygen, getting oxidized to $\text{H}_2\text{O}$. This reaction is an example of a redox reaction (reduction-oxidation reaction). It can also be classified as a single displacement reaction where $\text{H}_2$ displaces $\text{Cu}$.
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$\text{Fe(s) + CuSO}_4\text{(aq)} \rightarrow \text{FeSO}_4\text{(aq) + Cu(s)}$
In this reaction, iron ($\text{Fe}$) displaces copper ($\text{Cu}$) from its sulfate solution ($\text{CuSO}_4$). A more reactive metal displaces a less reactive metal from its salt solution. This is a clear example of a single displacement reaction.
Summary of Reaction Types
| Reaction | Type of Reaction | Explanation |
|---|---|---|
| $\text{CH}_4 \text{ + 2O}_2 \rightarrow \text{CO}_2 \text{ + 2H}_2\text{O}$ | Combustion | Substance reacts rapidly with oxygen. |
| $\text{2AgCl} \xrightarrow{\text{Sunlight}} \text{2Ag + Cl}_2$ | Decomposition | Single compound breaks down into simpler substances. |
| $\text{CuO + H}_2 \xrightarrow{\text{Heat}} \text{Cu + H}_2\text{O}$ | Redox / Single Displacement | Hydrogen reduces CuO; H$_2$ displaces Cu. |
| $\text{Fe + CuSO}_4 \rightarrow \text{FeSO}_4 \text{ + Cu}$ | Single Displacement | Iron displaces copper from its salt solution. |
Based on the analysis, the reaction where a single compound, silver chloride ($\text{AgCl}$), breaks down into simpler substances, silver ($\text{Ag}$) and chlorine ($\text{Cl}_2$), is the decomposition reaction.
Revision Table: Key Reaction Types
| Reaction Type | Definition | Example |
|---|---|---|
| Combination Reaction | Two or more substances combine to form a single substance. | $\text{C + O}_2 \rightarrow \text{CO}_2$ |
| Decomposition Reaction | A single compound breaks down into two or more simpler substances. | $\text{CaCO}_3 \xrightarrow{\text{Heat}} \text{CaO + CO}_2$ |
| Displacement Reaction | An element displaces another element in a compound. | $\text{Zn + H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 \text{ + H}_2$ |
| Double Displacement Reaction | Ions are exchanged between two compounds to form two new compounds. | $\text{AgNO}_3 \text{ + NaCl} \rightarrow \text{AgCl + NaNO}_3$ |
| Redox Reaction | Reactions involving both oxidation and reduction processes. | $\text{CuO + H}_2 \rightarrow \text{Cu + H}_2\text{O}$ |
| Combustion Reaction | Reaction with oxygen that produces heat and light. | $\text{CH}_4 \text{ + 2O}_2 \rightarrow \text{CO}_2 \text{ + 2H}_2\text{O}$ |
Additional Information on Decomposition Reactions
Decomposition reactions often require energy input in the form of heat, light, or electricity.
- Thermal decomposition: Decomposition caused by heat. Example: Heating calcium carbonate ($\text{CaCO}_3$) to form calcium oxide ($\text{CaO}$) and carbon dioxide ($\text{CO}_2$).
- Electrolytic decomposition: Decomposition caused by electricity. Example: Electrolysis of water ($\text{H}_2\text{O}$) to form hydrogen gas ($\text{H}_2$) and oxygen gas ($\text{O}_2$).
- Photolytic decomposition: Decomposition caused by light. Example: Decomposition of silver chloride ($\text{AgCl}$) in sunlight.
Decomposition reactions are important in various chemical processes, including extraction of metals, manufacturing of cement, and photographic development.
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?
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:
Fe2O3(s) + 2Al(s) → 2Fe(s) + Al2O3(s)
Which of the following statements about the given reaction is NOT correct?
Consider the following reaction:
2HgO \( \stackrel{\Delta}{\longrightarrow} \) 2Hg + O2
The respective state of HgO, Hg and O2 in the above reaction is
