Chemical energetics: Thermodynamics

Question 1

Entropy

Answer 1

A measure of the randomness or disorder of a system

Question 2

Factors affecting entropy, S

Answer 2

1. volume of gas
2. Melting / boiling
3. temperature of the system
4. Change in number of particles
5. Dissolving of a solid

Question 3

When volume of gas increases,

Answer 3

1. gas will spontaneously expand to occupy the entire container
2. In a larger volume of space, there are more ways to arrange the gas particles in the system
3. Gas expands from a less disordered system to a more disordered system
4. This gives rise to greater disorder
5. Hence, entropy of system increases, ^S is positive

Question 4

During melting / boiling,

Answer 4

1. solid lattice breaks down / molecules break away from the liquid’s surface
2. there are more ways to arrange the particles in the system
3. from a less disordered solid phase to a more disordered gaseous phase
4. This gives rise to greater disorder
5. Hence, entropy of system increases, ^S is positive

Question 5

When temperature of system increases,

Answer 5

1. system possesses more KE,
2. resulting in more ways to DISTRIBUTE the energy among the particles
3. It changes from a less disordered system to a more disordered system
4. This gives rise to greater disorder
5. Hence, entropy of system increases, ^S is positive

Question 6

When number of particles increases,

Answer 6

1. There is an increase in total number of gaseous molecules
2. There are more ways to arrange these particles in the system
3. It changes from a less disordered system to a more disordered sytem
4. This gives rise to greater disorder
5. Hence, entropy of system increases, ^S is positive

Question 7

When a solid dissolves,

Answer 7

1. Increase in disorder in the system due to ions breaking away from the lattice and arranging itself in the aqueous solution is greater than the decrease in disorder in the system when the water molecules surround the ions
2. There are more ways to arrange the particles in the system
3. It changes from a less disordered system to a more disordered system
4. This gives rise to greater disorder
5. Hence, entropy of system increases, ^S is positive

Question 8

Go Home To Sleep

Answer 8

^G = ^H - T^S

Question 9

Spontaneity

Answer 9

^G < 0 : reaction is energetically feasible. reaction is spontaneous

^G > 0 : reaction is not energetically feasible. reaction is not spontaneous

^G = 0 : reaction is in equilibrium. rate of forward reaction = rate of backward reaction

Question 10

Limitation of using ^G to determine spontaneity

Answer 10

Only valid under standard conditions