To determine which chemical reaction is a redox reaction, we need to examine each reaction and identify if there is a change in the oxidation states of any of the elements involved. A redox reaction involves the transfer of electrons between species, leading to changes in their oxidation states.
Let's go through each of the reactions step by step:
A) [tex]\( 2 \text{HCl} + \text{CaCO}_3 \rightarrow \text{CaCl}_2 + \text{CO}_2 + \text{H}_2\text{O} \)[/tex]
- H in HCl: Oxidation state +1
- Cl in HCl: Oxidation state -1
- Ca in CaCO[tex]\(_3\)[/tex]: Oxidation state +2
- C in CaCO[tex]\(_3\)[/tex]: Oxidation state +4
- O in CaCO[tex]\(_3\)[/tex]: Oxidation state -2
In the products:
- Ca in CaCl[tex]\(_2\)[/tex]: Oxidation state +2
- Cl in CaCl[tex]\(_2\)[/tex]: Oxidation state -1
- C in CO[tex]\(_2\)[/tex]: Oxidation state +4
- O in CO[tex]\(_2\)[/tex]: Oxidation state -2
- H in H[tex]\(_2\text{O}\)[/tex]: Oxidation state +1
- O in H[tex]\(_2\text{O}\)[/tex]: Oxidation state -2
Since there is no change in the oxidation states of the elements, this is not a redox reaction.
B) [tex]\( \text{AgNO}_3 + \text{KCl} \rightarrow \text{AgCl} + \text{KNO}_3 \)[/tex]
- Ag in AgNO[tex]\(_3\)[/tex]: Oxidation state +1
- N in AgNO[tex]\(_3\)[/tex]: Oxidation state +5
- O in AgNO[tex]\(_3\)[/tex]: Oxidation state -2
- K in KCl: Oxidation state +1
- Cl in KCl: Oxidation state -1
In the products:
- Ag in AgCl: Oxidation state +1
- Cl in AgCl: Oxidation state -1
- K in KNO[tex]\(_3\)[/tex]: Oxidation state +1
- N in KNO[tex]\(_3\)[/tex]: Oxidation state +5
- O in KNO[tex]\(_3\)[/tex]: Oxidation state -2
Since there is no change in the oxidation states of the elements, this is not a redox reaction.
C) [tex]\( \text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O} \)[/tex]
- Ca in Ca(OH)[tex]\(_2\)[/tex]: Oxidation state +2
- O in Ca(OH)[tex]\(_2\)[/tex]: Oxidation state -2
- H in Ca(OH)[tex]\(_2\)[/tex]: Oxidation state +1
- C in CO[tex]\(_2\)[/tex]: Oxidation state +4
- O in CO[tex]\(_2\)[/tex]: Oxidation state -2
In the products:
- Ca in CaCO[tex]\(_3\)[/tex]: Oxidation state +2
- C in CaCO[tex]\(_3\)[/tex]: Oxidation state +4
- O in CaCO[tex]\(_3\)[/tex]: Oxidation state -2
- H in H[tex]\(_2\text{O}\)[/tex]: Oxidation state +1
- O in H[tex]\(_2\text{O}\)[/tex]: Oxidation state -2
Since there is no change in the oxidation states of the elements, this is not a redox reaction.
D) [tex]\( 2 \text{H}_2 + \text{O}_2 \rightarrow 2 \text{H}_2\text{O} \)[/tex]
- H in H[tex]\(_2\)[/tex]: Oxidation state 0 (elemental form)
- O in O[tex]\(_2\)[/tex]: Oxidation state 0 (elemental form)
In the product:
- H in H[tex]\(_2\text{O}\)[/tex]: Oxidation state +1
- O in H[tex]\(_2\text{O}\)[/tex]: Oxidation state -2
Here, the oxidation state of hydrogen changes from 0 to +1 and the oxidation state of oxygen changes from 0 to -2. This indicates that electrons are transferred—hydrogen is oxidized and oxygen is reduced.
Therefore, reaction D is a redox reaction.
Conclusion:
The redox reaction among the given options is:
[tex]\[ 2 \text{H}_2 + \text{O}_2 \rightarrow 2 \text{H}_2\text{O} \][/tex]
The correct answer is D.
