Answer :
To determine which of these reactions are redox reactions, we need to check if there is a change in the oxidation states of the elements involved in the reactions. A redox reaction is defined as a reaction where oxidation and reduction occur simultaneously, meaning there is a transfer of electrons between species. Let's analyze each reaction step-by-step:
1. Reaction: [tex]\( Cd + HCl \rightarrow CdCl_2 + H_2 \)[/tex]
- Cadmium (Cd): In elemental state (Cd) its oxidation state is 0. In [tex]\( CdCl_2 \)[/tex], cadmium's oxidation state is +2.
- Hydrogen (H): In [tex]\( HCl \)[/tex] hydrogen's oxidation state is +1. In [tex]\( H_2 \)[/tex], hydrogen's oxidation state is 0.
- Chlorine (Cl): In [tex]\( HCl \)[/tex], chlorine’s oxidation state is -1. In [tex]\( CdCl_2 \)[/tex], chlorine’s oxidation state remains -1.
_Changes in oxidation states:_
- Cadmium: [tex]\( 0 \rightarrow +2 \)[/tex] (oxidation)
- Hydrogen: [tex]\( +1 \rightarrow 0 \)[/tex] (reduction)
This reaction is a redox reaction.
2. Reaction: [tex]\( CuCl_2 + Na_2S \rightarrow 2 NaCl + CuS \)[/tex]
- Copper (Cu): In [tex]\( CuCl_2 \)[/tex], copper's oxidation state is +2. In [tex]\( CuS \)[/tex], copper's oxidation state is still +2.
- Sodium (Na): In [tex]\( Na_2S \)[/tex], sodium’s oxidation state is +1. In [tex]\( NaCl \)[/tex], sodium's oxidation state is +1.
- Sulfur (S): In [tex]\( Na_2S \)[/tex], sulfur’s oxidation state is -2. In [tex]\( CuS \)[/tex], sulfur's oxidation state is -2.
- Chlorine (Cl): In [tex]\( CuCl_2 \)[/tex], chlorine’s oxidation state is -1. In [tex]\( NaCl \)[/tex], chlorine’s oxidation state is -1.
_Changes in oxidation states:_
- No changes in the oxidation states of any of the elements.
This reaction is not a redox reaction.
3. Reaction: [tex]\( CaCO_3 \rightarrow CaO + CO_2 \)[/tex]
- Calcium (Ca): In [tex]\( CaCO_3 \)[/tex], calcium's oxidation state is +2. In [tex]\( CaO \)[/tex], calcium’s oxidation state is still +2.
- Carbon (C): In [tex]\( CaCO_3 \)[/tex], carbon’s oxidation state is +4. In [tex]\( CO_2 \)[/tex], carbon’s oxidation state is still +4.
- Oxygen (O): In [tex]\( CaCO_3 \)[/tex], oxygen’s oxidation state is -2. In [tex]\( CaO \)[/tex] and [tex]\( CO_2 \)[/tex], oxygen's oxidation state remains -2.
_Changes in oxidation states:_
- No changes in the oxidation states of any of the elements.
This reaction is not a redox reaction.
4. Reaction: [tex]\( 2 ZnS + 3 O_2 \rightarrow 2 ZnO + 2 SO_2 \)[/tex]
- Zinc (Zn): In [tex]\( ZnS \)[/tex], zinc’s oxidation state is +2. In [tex]\( ZnO \)[/tex], zinc's oxidation state remains +2.
- Sulfur (S): In [tex]\( ZnS \)[/tex], sulfur’s oxidation state is -2. In [tex]\( SO_2 \)[/tex], sulfur’s oxidation state is +4.
- Oxygen (O): In [tex]\( O_2 \)[/tex], oxygen’s oxidation state is 0. In [tex]\( ZnO \)[/tex], and [tex]\( SO_2 \)[/tex], oxygen’s oxidation state is -2.
_Changes in oxidation states:_
- Sulfur: [tex]\( -2 \rightarrow +4 \)[/tex] (oxidation)
- Oxygen: [tex]\( 0 \rightarrow -2 \)[/tex] (reduction)
This reaction is a redox reaction.
5. Reaction: [tex]\( CH_4 + 2 O_2 \rightarrow CO_2 + 2 H_2O \)[/tex]
- Carbon (C): In [tex]\( CH_4 \)[/tex], carbon's oxidation state is -4. In [tex]\( CO_2 \)[/tex], carbon's oxidation state is +4.
- Hydrogen (H): In [tex]\( CH_4 \)[/tex], hydrogen’s oxidation state is +1. In [tex]\( H_2O \)[/tex], hydrogen’s oxidation state remains +1.
- Oxygen (O): In [tex]\( O_2 \)[/tex], oxygen’s oxidation state is 0. In [tex]\( CO_2 \)[/tex] and [tex]\( H_2O \)[/tex], oxygen's oxidation state is -2.
_Changes in oxidation states:_
- Carbon: [tex]\( -4 \rightarrow +4 \)[/tex] (oxidation)
- Oxygen: [tex]\( 0 \rightarrow -2 \)[/tex] (reduction)
This reaction is a redox reaction.
Conclusion:
The redox reactions are:
- [tex]\( Cd + HCl \rightarrow CdCl_2 + H_2 \)[/tex]
- [tex]\( 2 ZnS + 3 O_2 \rightarrow 2 ZnO + 2 SO_2 \)[/tex]
- [tex]\( CH_4 + 2 O_2 \rightarrow CO_2 + 2 H_2O \)[/tex]
1. Reaction: [tex]\( Cd + HCl \rightarrow CdCl_2 + H_2 \)[/tex]
- Cadmium (Cd): In elemental state (Cd) its oxidation state is 0. In [tex]\( CdCl_2 \)[/tex], cadmium's oxidation state is +2.
- Hydrogen (H): In [tex]\( HCl \)[/tex] hydrogen's oxidation state is +1. In [tex]\( H_2 \)[/tex], hydrogen's oxidation state is 0.
- Chlorine (Cl): In [tex]\( HCl \)[/tex], chlorine’s oxidation state is -1. In [tex]\( CdCl_2 \)[/tex], chlorine’s oxidation state remains -1.
_Changes in oxidation states:_
- Cadmium: [tex]\( 0 \rightarrow +2 \)[/tex] (oxidation)
- Hydrogen: [tex]\( +1 \rightarrow 0 \)[/tex] (reduction)
This reaction is a redox reaction.
2. Reaction: [tex]\( CuCl_2 + Na_2S \rightarrow 2 NaCl + CuS \)[/tex]
- Copper (Cu): In [tex]\( CuCl_2 \)[/tex], copper's oxidation state is +2. In [tex]\( CuS \)[/tex], copper's oxidation state is still +2.
- Sodium (Na): In [tex]\( Na_2S \)[/tex], sodium’s oxidation state is +1. In [tex]\( NaCl \)[/tex], sodium's oxidation state is +1.
- Sulfur (S): In [tex]\( Na_2S \)[/tex], sulfur’s oxidation state is -2. In [tex]\( CuS \)[/tex], sulfur's oxidation state is -2.
- Chlorine (Cl): In [tex]\( CuCl_2 \)[/tex], chlorine’s oxidation state is -1. In [tex]\( NaCl \)[/tex], chlorine’s oxidation state is -1.
_Changes in oxidation states:_
- No changes in the oxidation states of any of the elements.
This reaction is not a redox reaction.
3. Reaction: [tex]\( CaCO_3 \rightarrow CaO + CO_2 \)[/tex]
- Calcium (Ca): In [tex]\( CaCO_3 \)[/tex], calcium's oxidation state is +2. In [tex]\( CaO \)[/tex], calcium’s oxidation state is still +2.
- Carbon (C): In [tex]\( CaCO_3 \)[/tex], carbon’s oxidation state is +4. In [tex]\( CO_2 \)[/tex], carbon’s oxidation state is still +4.
- Oxygen (O): In [tex]\( CaCO_3 \)[/tex], oxygen’s oxidation state is -2. In [tex]\( CaO \)[/tex] and [tex]\( CO_2 \)[/tex], oxygen's oxidation state remains -2.
_Changes in oxidation states:_
- No changes in the oxidation states of any of the elements.
This reaction is not a redox reaction.
4. Reaction: [tex]\( 2 ZnS + 3 O_2 \rightarrow 2 ZnO + 2 SO_2 \)[/tex]
- Zinc (Zn): In [tex]\( ZnS \)[/tex], zinc’s oxidation state is +2. In [tex]\( ZnO \)[/tex], zinc's oxidation state remains +2.
- Sulfur (S): In [tex]\( ZnS \)[/tex], sulfur’s oxidation state is -2. In [tex]\( SO_2 \)[/tex], sulfur’s oxidation state is +4.
- Oxygen (O): In [tex]\( O_2 \)[/tex], oxygen’s oxidation state is 0. In [tex]\( ZnO \)[/tex], and [tex]\( SO_2 \)[/tex], oxygen’s oxidation state is -2.
_Changes in oxidation states:_
- Sulfur: [tex]\( -2 \rightarrow +4 \)[/tex] (oxidation)
- Oxygen: [tex]\( 0 \rightarrow -2 \)[/tex] (reduction)
This reaction is a redox reaction.
5. Reaction: [tex]\( CH_4 + 2 O_2 \rightarrow CO_2 + 2 H_2O \)[/tex]
- Carbon (C): In [tex]\( CH_4 \)[/tex], carbon's oxidation state is -4. In [tex]\( CO_2 \)[/tex], carbon's oxidation state is +4.
- Hydrogen (H): In [tex]\( CH_4 \)[/tex], hydrogen’s oxidation state is +1. In [tex]\( H_2O \)[/tex], hydrogen’s oxidation state remains +1.
- Oxygen (O): In [tex]\( O_2 \)[/tex], oxygen’s oxidation state is 0. In [tex]\( CO_2 \)[/tex] and [tex]\( H_2O \)[/tex], oxygen's oxidation state is -2.
_Changes in oxidation states:_
- Carbon: [tex]\( -4 \rightarrow +4 \)[/tex] (oxidation)
- Oxygen: [tex]\( 0 \rightarrow -2 \)[/tex] (reduction)
This reaction is a redox reaction.
Conclusion:
The redox reactions are:
- [tex]\( Cd + HCl \rightarrow CdCl_2 + H_2 \)[/tex]
- [tex]\( 2 ZnS + 3 O_2 \rightarrow 2 ZnO + 2 SO_2 \)[/tex]
- [tex]\( CH_4 + 2 O_2 \rightarrow CO_2 + 2 H_2O \)[/tex]
