Chapter 18, Problem 1SAQ

Interpretation Introduction

Introduction: A gas has greater entropy than a solid because in a gaseous state, the molecules are free to move in any direction while in solid state, the movement of molecules are restricted.

Answer to Problem 1SAQ

Solution:

The reaction given in option (a) will have a positive $\Delta S_{sys}$.

Explanation of Solution

The phase transition is from solid to gas during the chemical reaction, so entropy increases and $\Delta S_{sys}$ will be positive.The number of moles of gas decrease during a chemical reaction; 12 mol of gas have decreased to 6 moles, so the entropy decreases and $\Delta S_{sys}$ will be negative.

The number of moles of gas decrease during a chemical reaction; 2 mol of gas have decreased to 1 mol, so the entropy decreases and $\Delta S_{sys}$ will be negative.

The number of moles of gas decrease during a chemical reaction; 3 mol of gas have decreased to 1 mol, so the entropy decreases and $\Delta S_{sys}$ will be negative

Conclusion

Thus, the reaction given in option (a) will have a positive $\Delta S_{sys}$ and the correct answer is option (a).