Question

Which statements are true?
1. ${S^{\circ}}$ values of all elements in their states are positive
2. ${S^{\circ}}$ values of all aqueous ions are positive
3.$\Delta {S^{\circ}}$ values for all spontaneous reactions are positive
A) 1 only
B) 1 and 2 only
C) 2 and 3 only
D) All of these

Answer 1

Hint:
Entropy of a substance represents the randomness in the molecules of the element or the compound. ${S^{\circ}}$ gives the standard entropy of the system and is calculated under standard conditions.

Complete step by step solution:
The particles (atoms, molecules, and ions) composing a chemical system undergo various types of molecular motion, namely translational motion, rotational motion, and vibrational motion. The greater is the molecular motion in a system, the greater is the number of microstates of the element possible and thus higher is its entropy.
Considering statement 1,
We know that in standard states, the particles in elements undergo some amount of motion. Since, there is a randomness in the molecules (no matter how small), the entropy of the system will be positive. Thus we can say that statement 1 is true.
Considering statement 2,
We know that ions in an aqueous solution tend to move and thus must have a positive entropy as well. But in aqueous solutions, entropy of ions are calculated relative to the entropy of a hydrogen ion solution. Thus, they can have negative values for entropy as well. Statement 2 is not correct.
Considering statement 3,
For a spontaneous reaction the free energy change must be negative always. Depending upon the values of enthalpy change and the temperature, the entropy change can take either positive or negative values. Statement 3 is not correct.

Thus, the correct answer is A.

Note:
The entropy is zero for a perfectly ordered system with only a single microstate available to it. This criterion is met only by a perfect crystal at a temperature of zero kelvin, that is, the absolute zero, in which each component particle remains fixed in its place within the crystal lattice and exhibits no motion at all.