Chemical Energetics II

Question 1

Spontaneous process

2 natural tendencies

Answer 1

Is a process that once started will continue without any external assistance

Tendency to achieve lower energy state and tendency toward state of greater entropy causes spontaneous reactions

Question 2

Entropy

Answer 2

Measure of the disorder in a system, the more disordered it is, the larger its entropy

Question 3

Entropy change and what it means

Answer 3

Measure of change in disorder in system, depending on entropy of final state subtracted by entropy of initial state

Positive entropy change means that final state is more disordered than initial state, while negative entropy change means that initial state is more disordered than final state

Question 4

Factors affecting entropy of system

Answer 4

entropy of solid < entropy of liquid &laquo_space;entropy of gas

temperature increase, entropy of a system increase

no. of particles in system increase, entropy of system increase

mixing in GAS and LIQUID increases entropy but increase/ decrease in disorder in SOLID depending on constituent ions

Question 5

change in state explanation

Answer 5

• molecules in _____ can move more freely/ and more randomly arranged
• more ways to arrange molecules in ___ state than ___ state
• greater disorder hence greater entropy of system
• (in gas) large increase in volume is also accompanied

Question 6

change in number of particles (especially gases)

Answer 6

• increase in number of moles of gaseous molecules in the system from __ to __ moles
• more gaseous molecules which can more randomly, more ways to arrange them
• more ways to distribute energy in system
• disorder increases and entropy increases

Question 7

change in temperature

Answer 7

boltzmann energy distribution broadens (maximum of curve displaced to right and lower, greater spread of kinetic energies)
more possible energy states in which particles can adopt at higher temperature
more ways to arrange energy quanta in the hotter system, hence entropy increases

Question 8

mixing of gas particles

Answer 8

gases mix completely to create a more disordered state
each gas expands to occupy the whole container
more ways for molecules to arrange themselves in larger volume
increase in entropy

Question 9

mixing of liquid particles

Answer 9

liquids of similiar polarities form solution where molecules are randomly mixed
solutions greater disorder than liquids in unmixed state
increased entropy and more ways for molecules to arrange themselves in larger volume of solution

Question 10

dissolution of ionic solid in water

Answer 10

net increase or decrease:

disruption of crystal increases disorder since ions previously rigidly held in solid lattice are free to move about

hydration process decreases disorder because it puts hydrating water molecules into an orderly arrangement

OVERALL DEPENDS ON: charge of ions = how many water molecules can be bonded

Question 11

if nothing

Answer 11

close to zero because:
- reaction does not cause change in number of moles of particles in system
- no phase change in any substance
- little change in number of ways to arrange particles in system
- entropy of system remains almost same