Chemical Energetics 2

Question 1

What is a spontaneous process?

Answer 1

A spontaneous process is one that once started, will continue without any external assistance.

Question 2

What are the two tendencies behind spontaneous processes?

Answer 2

The tendency to achieve a lower state of energy and the tendency toward a state of greater entropy.

Question 3

What is entropy of a system?

Answer 3

A measure of the disorder of matter and energy in the system. The more ways matter can be arranged and the more ways energy in the system can be dispersed, the more disordered the system is and the larger is its entropy.

Question 4

What is the equation for entropy change?

Answer 4

ΔS = Sfinal - Sinitial

Question 5

What does the value of entropy change say about the disorder of the system?

Answer 5

ΔS<0, final state is less disordered than initial state

ΔS>0, final state is more disordered than initial state

Question 6

What are the factors affecting entropy of a system?

Answer 6

1. Change in temperature
2. Change in phase
3. Change in number of particles
4. Mixing of particles

Question 7

How does a change in temperature affect entropy?

Answer 7

An increase in temperature increases entropy because of the broadening of the Boltzmann energy distribution, there are more energy states in which the particles can adopt at a higher temperature.

Question 8

How does a change in phase affect entropy?

Answer 8

Ssolid

Question 9

How does change in number of particles affect entropy?

Answer 9

The entropy increases as number of particles increases. With more particles, there are more ways to arrange the particles and more ways to distribute the energy in the system, creating greater disorder. For processes that result in an increase in number of moles of gaseous particles, entropy increases more significantly.

Question 10

How does mixing of particles affect entropy?

Answer 10

1. Mixing of gases: Entropy increases as the gas expands to occupy the whole container and there are more ways for molecules to arrange themselves in the larger volume.
2. Mixing of liquids: Entropy increases as there are more ways for molecules to arrange themselves in the larger volume of solution, causing the solution to have a greater disorder than the individual liquids unmixed.
3. Dissolution of an ionic solid in water: Dissolving ions involves disruption of the lattice and hydration of ions. The disruption increases disorder as the previously rigidly held ions are free to move about. The hydration decreases disorder as water molecules are put in an orderly arrangement around the ions. The more highly charged the ions, the more water molecules are ordered about the ions, the lower the entropy.

Question 11

What are the equations for Standard Gibb’s Free Energy change and Gibb’s Free Energy change?

Answer 11

ΔG⦵=ΔH⦵-TΔS⦵

ΔG=ΔH-TΔS

Question 12

How do the signs of ΔG⦵ and ΔG show if the reaction is spontaneous?

Answer 12

If ΔG⦵/ΔG<0, reaction is exergonic and the reaction is spontaneous.
If ΔG⦵/ΔG>0, reaction is endergonic and the reaction is not spontaneous.
If ΔG⦵/ΔG=0, the system is at an equilibrium.

Question 13

How does temperature affect spontaneity of a reaction?

Answer 13

ΔH<0 and ΔS>0, it is spontaneous at all temperatures.
ΔH>0 and ΔS>0, it is spontaneous at high temperatures.
ΔH<0 and ΔS<0, it is spontaneous at low temperatures.
ΔH>0 and ΔS<0, it is not spontaneous at all temperatures.