Question

Which of the following has the highest entropy?
(A) Mercury
(B) Hydrogen
(C) Water
(D) Graphite

Answer 1

Hint: We will check each of the options for the state in which they occur at room temperature. The entropy sequence for different states is: Gas > Liquid > Solids. This is so because in a gaseous state the particles are loosely bonded while in solid state the particles are strongly bonded.

Complete step by step answer:
-First of all we will see what entropy is.
Entropy is an extensive property of any thermodynamic system. Basically it is the measure of the randomness or disorderness of a system. From the thermodynamic point of view entropy describes the behaviour of any system on the basis of its thermodynamic properties like temperature, heat capacity, pressure and entropy. This description is also done for the equilibrium state of the systems.
We should also remember that entropy is a thermodynamic function which depends on the state of the system, not the path followed by it. We represent entropy by ‘S’ and in standard state as ${S^ \circ }$. Its SI unit is J/Kmol.
-For an isolated system, entropy is higher because it has greater entropy. When during a chemical reaction a reactant breaks down into more number of products, entropy also increases. Also the entropy of any system at higher temperatures is much more than that at lower temperatures.
Also the entropy order of various states is: Gas > Liquid > Solid
The entropy of gaseous state is highest because the particles are loosely bound with each other and so their randomness is higher. But in solid state the particles are much strongly and closely bonded to each other so randomness in this state is lowest.
-We will now check for the options and identify their states to check which of them has the highest entropy.
For (A) Mercury: It is the only metal present as liquid at room temperature.
For (B) Hydrogen: Hydrogen is present in gaseous state at room temperature and so will have high randomness. So, its entropy will be highest.
For (C) Water: At room temperatures water is present in liquid state.
For (D) Graphite: At room temperature graphite is found in solid state. Hence its randomness will be the least.
In the above discussion we have seen that only hydrogen is present in a gaseous state and so its randomness is high. Hence its entropy will also be the highest among all other options.

Hence the correct option will be: (B) Hydrogen.

Note: During a reaction there occurs an entropy change which can be calculated as sum of the entropy change of system and surroundings. The sign of the value of $\Delta S$ tells us whether the reaction is spontaneous or nonspontaneous.
If $\Delta {S_{total}}$ = positive (+ve); the process is spontaneous and a spontaneous process is thermodynamically irreversible.
 If $\Delta {S_{total}}$ = negative (-ve); the process is nonspontaneous.
If $\Delta {S_{total}}$ = 0; the process is at equilibrium.