Question

Ethanol, C2H5OH, will combust in air according to the equation below. C2H5OH(l) + 3 O2(g) → 2 CO2(g) + 3 H2O(g) ΔHo = –1270 kJ/molrxn (a) Is O2(g) oxidized in the reaction, or is it reduced? Justify your answer in terms of oxidation numbers.

Answer 1

Answer:

O2(g) was Reduced

Explanation:

It is necessary at this point to restate the working definitions of oxidation and reduction.

Oxidation refers to increase in oxidation number. A chemical specie is oxidized in a chemical reaction if there is a positive increase in its oxidation number from left to right in the reaction.

A chemical specie is said to be reduced when there is a decrease in its oxidation number from left to right in a reaction. Hence reduction refers to a decrease in oxidation number.

Now let us focus on O2(g). Its oxidation number on the left hand side is zero. On the right hand side, its oxidation number decreases to -2. This shows a decrease in oxidation number. From our premises above, we can safely conclude that O2(g) was reduced in the reaction.