State a reason why, when hydrogen is passed over heated copper oxide, the resultant product formed, differs in colour from the original reactant.
\[\ce{\underset{\text{Black}}{CuO} + H2 ->[heat]\underset{\text{Reddish brown}}{Cu} + H2O}\]
H2 removes oxygen from CuO and reduces it to Cu metal (reddish brown in colour).
Concept: Oxidation, Reduction and Redox Reactions
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