Question

When hydrogen gas is passed over heated copper ($II$) oxide, copper and steam are formed. Write the balanced chemical equation for this reaction and state (i) the substance oxidized and (ii) the substance reduced in this reaction.

Answer 1

Hint: The balanced chemical reaction can be written by checking that both the reactant side and the product side have the same number of atoms of each element.
Reduction is the process of losing oxygen or gaining hydrogen, while oxidation is the process of gaining oxygen or losing hydrogen.

Complete step by step answer:
Let us first write the reactants and products they are given to us on the left and right sides of the equation respectively. The reactant side has copper oxide and hydrogen gas and the product side has copper and steam. Thus, we have:
${H_2} + CuO \to Cu + {H_2}O$
Now let us count the number of atoms of each element on both sides. There are two hydrogens on both sides, two copper atoms on both sides and one oxygen atom on both sides. Hence, since both sides have equal numbers of atoms, the equation is already balanced.
As we know, substances getting oxidized are the ones which gain oxygen. As we can see, hydrogen is gaining oxygen to form steam. Thus, the substance getting oxidized is hydrogen.
Similarly, we know that substances getting reduced lose oxygen. Since in this reaction, copper oxide is losing its oxygen to form copper, the substance getting reduced is copper.
Hence, the set of answers are:
${H_2} + CuO \to Cu + {H_2}O$
(i) Hydrogen
(ii) Copper

Note: These types of reactions, in which oxidation and reduction happen simultaneously, are known as redox reactions. We can also find the substances getting oxidized and reduced by checking the change in oxidation state of each element. Elements which get oxidised attain a higher oxidation state, while the ones getting reduced have their oxidation states lowered.