If we immerse a strip of zinc metal in an equeous solution of copper sulphate we notice that

Options

A. a dark coloured solid deposits on the surface of the zinc
B. blue colour characteristic of the `Cu^(2+)` ions slowly disappears from the solution
C. the enthalpy of reaction is lost to the surroundings as heat
D. All of these

Answer

D

Explanation

Chemical analysis shows that the dark colured deposit is finely divided copper metal abnd that the solution now contains zinc ions. Therefore the reaction is
`Zn(s)+Cu^(2+)(aq.) rarr Zn^(2+)(aq.)+Cu(s)`
This is a redox reaction is which `Zn` metal is oxidized to `Zn^(2+)` and `Cu^(2+)` ion is reduced to `Cu`. Recall that an oxidation is a loss of electrons (an increase in oxidation number) and a reduction is a gain of electrons (a decrease in oxidation number).
Since electrons are transferred directly from `Zn` to `Cu^(2+)`, the enthalpy of reaction is lost to the surroundings. However, if the reaction is carried out using the electrochemical cell then some of the chemical enerfy released by the reaction is converted to electrical energy, which can be used to light a light bulb or run an electric motor.