Question

Why is the extraction of copper from pyrites more difficult than that from its oxide ore through reduction?

Answer 1

Hint: To solve this question, use the concept of Gibbs free energy. It is a parameter used to measure the energy which is available to do useful work. The reaction with a more negative Gibbs free energy will be more spontaneous.

Complete step by step answer:
Extraction of Copper is generally done from two types of copper ores –
Pyrites ore – It is also known as chalcocite- \[C{{u}_{2}}S\]. It is a sulfide mineral, which occurs as a brass yellow compound.
Oxide ore – It is also known as Cuprite- \[C{{u}_{2}}O\]. It is an oxide mineral which occurs as a dark red to black coloured crystal.
We measure the available/free energy to a work in terms of Gibbs free energy. Lesser the Gibbs free energy, more is its feasibility.
Oxide ore of copper easily gets reduced to form elemental copper. Gibbs free energy is quite low. Gibbs free energy (formation) of Copper Oxide is greater than that of Carbon monoxide. Also, this reaction occurs in a single step.
\[C(s)+C{{u}_{2}}O(s)\to 2Cu(s)+CO(g)\]
The Gibbs free energy for the formation of Copper sulphate is lesser than that of Carbon disulfide and hydrogen sulfide . Hence reduction of copper sulphate to elemental copper is difficult. Also, this reaction occurs in two steps, i.e. by converting it into oxide first through roasting or smelting. And then, convert the oxides to metallic copper via oxidation.
\[C{{u}_{2}}S+{{H}_{2}}\to 2Cu+{{H}_{2}}S\]
\[2C{{u}_{2}}S+C\to 4Cu+C{{S}_{2}}\]
Therefore, we can say that extraction of copper from pyrites is more difficult than that from its oxide ore through reduction.

Additional Information:
A graph between Gibbs Free energy and temperature is known as Ellingham diagram.

Note: Gibbs free energy \[(\Delta G)\] is an extensive property and a state function. It can also be expressed in terms of enthalpy \[(\Delta H)\], temperature \[T\] and entropy \[(\Delta S)\] as –
\[(\Delta G)=(\Delta H)-T(\Delta S)\].
Enthalpy is the total heat change occurring in the system.
Entropy is a measure of randomness or disorder in the system.