Consider the following reaction:
[tex]\[CO_2(g) + H_2(g) \longrightarrow CO(g) + H_2O(l)\][/tex]

What is being oxidized?
A. carbon
B. carbon dioxide
C. oxygen
D. hydrogen



Answer :

To determine what is being oxidized in the reaction:

[tex]\[\text{CO}_2(g) + \text{H}_2(g) \longrightarrow \text{CO}(g) + \text{H}_2\text{O}(l)\][/tex]

we need to analyze the changes in oxidation states of the elements involved in the reaction.

1. Oxidation State of Carbon in CO₂ (carbon dioxide):
- In CO₂, each oxygen has an oxidation state of -2.
- Since there are two oxygens, the total oxidation state contributed by oxygen is \(2 \times -2 = -4\).
- To balance this, the oxidation state of carbon must be +4.
- Thus, the oxidation state of carbon in CO₂ is +4.

2. Oxidation State of Hydrogen in H₂ (molecular hydrogen):
- In its elemental form, hydrogen has an oxidation state of 0.
- Thus, the oxidation state of hydrogen in H₂ is 0.

3. Oxidation State of Carbon in CO (carbon monoxide):
- In CO, oxygen has an oxidation state of -2.
- To balance this, the oxidation state of carbon must be +2.
- Thus, the oxidation state of carbon in CO is +2.

4. Oxidation State of Hydrogen in H₂O (water):
- In H₂O, oxygen has an oxidation state of -2.
- There are two hydrogens, each usually having an oxidation state of +1.
- Thus, the oxidation state of each hydrogen in H₂O is +1.

Now, we compare the changes in oxidation states from the reactants to the products:

- Carbon:
- It goes from +4 in CO₂ to +2 in CO.
- A decrease in oxidation state means that carbon is being reduced, not oxidized.

- Hydrogen:
- It goes from 0 in H₂ to +1 in H₂O.
- An increase in oxidation state means that hydrogen is being oxidized.

Hence, the element whose oxidation state increases is hydrogen. Therefore, the substance being oxidized in this reaction is hydrogen.

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