Question

brown substance 'X' on heating in air forms a substance Y. When hydrogen gas is passed over heated 'Y' it again changes into 'X'.                                                                                                   

(I) Name the substances X and Y

(ii) Name the chemical processes occurring during the two changes

(iii) Write the chemical equations.

Answer 1

(I) Substance X is 'Copper' and substance Y is 'Copper oxide'.

(ii) The chemical process occurring during the two changes is:-
Oxidation and reduction.

(iii) The chemical equations involved are:-
2Cu (s) + O2 (g) ----> 2CuO
CuO + H2 (g) ----> Cu + H2O


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Answer 2

The brown substance

'X' is copper, which becomes Cu when heated copper oxide is formed. Therefore, compound  "Y"  is copper oxide.  

Explanation:

• This brown substance is copper because it is brown in color and forms copper oxide when it passes through oxygen in the presence of heat and forms copper again when it reacts with hydrogen. The reaction is as follows. It's a combination reaction.

$2Cu + O2----2CuO$

• When hydrogen gas passes through heated copper

(2CuO), a reverse reaction occurs and copper is formed, so the black coating on the surface turns brown. The chemical reaction is as follows:

$CuO + H2 ----- Cu + H2O$

• The reactions performed here are oxidation and reduction. Also known as a redox reaction.

$2Cu + O2 ----- 2CuO$ (oxidation)

2CuO + H2 → Cu + H20  Heating (reduction)

• During this reaction,  copper oxide loses oxygen and is reduced. Hydrogen absorbs oxygen and is oxidized. In other words, one reactant is oxidized and the other reactant is reduced.

Note: it is a redox reaction in which electrons move between two species. Oxidation of molecules by removing hydrogen or binding to oxygen usually releases large amounts of energy. Using this approach, you can easily solve questions related to redox reactions.

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