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Physical Chemistry > Quiz 3: Chapter 4 > Flashcards

Quiz 3: Chapter 4 Flashcards

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1
Q

What does Clausius say?

A

The entropy of an isolated system always increases in the course of a spontaneous process

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2
Q

What is the Clausius equation?

A
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3
Q

What is ΔGsys? What type is it? What type of equation is it? What is it best thought of as?

A
  • ∆𝐺_sys is the change in Gibbs free energy.
  • Gibbs free energy is not a “normal energy” because it is not conserved (if a spontaneous process occurs in the universe, the Gibbs free energy of the universe becomes more negative).
  • The Gibbs equation is an “all-entropy” equation.
  • ∆𝐺_sys is best thought of as the “dispersible amount of energy” or the “maximum non-pV work”.
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4
Q

How do you calculate the free energy change during the expansion/compression of a gas?

A
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5
Q

What is Q?

A

the reaction quotient

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6
Q

What is K?

A

the equilibrium quotient

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7
Q

Describe Q and K at equilibrium

A

At equilibrium ….
the partial pressures of the quotient Q correspond to the equilibrium partial pressures.
Therefore, Q = K and the Gibbs free energy is zero per definition ∆𝐺=0.

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8
Q

What is the standard gibbs free energy equation? What does this value represent?

A
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9
Q

Explain what the ratio of Q and K means for gibbs free energy.

A
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10
Q

What is one way Gibbs free energy can be interpreted?

A
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11
Q

Give an example of a partial molar quantity.

A

chemical potential

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12
Q

What is the best way to rationalize a partial molar property?

A

“the partial molar volume”

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13
Q

What is partial molar volume?

A
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14
Q

What does the partial molar volume depend on?

A

depends on how molecules pack in the liquid

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15
Q

Partial molar volume is ___________

A
  • a derivative
  • The partial molar volume of a substance A is the slope of the plot of the total volume as the amount of A is changed.
  • The partial molar volume is not necessarily positive (addition of MgSO4 into water leads to a slight reduction of the total volume).
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16
Q

How do volumes of mixtures change? How can this change be calculated?

A
  • the total volume of any mixture is the partial molar volumes at the composition of the mixture multiplied by the amounts.
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17
Q

What is chemical potential? What is the equation? What is the graph?

A
  • The chemical potential of a substance A in a mixture is defined as the partial molar Gibbs energy
  • The chemical potential is the contribution of that substance to the total Gibbs free energy
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18
Q

What is the fundamental equation of chemical thermodynamics? What happens to this equation under constant temperature and pressure?

A
  • First two terms are dropped under constant T and P
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19
Q

What is 𝜉?

A

extent of reaction

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20
Q

What are the two interpretations of ∆𝑟𝐺?

A
  • As a derivative and a difference
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21
Q

The free energy change for the reversible and isothermal expansion/compression of an ideal gas is:

A

Entirely entropic

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22
Q

What is the chemical potential of gas A in a mixture of ideal gases?

A
23
Q

How are chemical potential and molar gibbs free energy related?

A
24
Q

What is the origin of the minimum on this graph?

A

The Gibbs free energy of mixing (dilution) give rise to a minimum in the plot of ∆𝑟𝐺 vs the extent of the reaction, which is the equilibrium position defined by K

25
Q

What does the Van’t Hoff equation describe?

A

describes the T-dependence of the equilibrium constant

26
Q

Explain the relationship between enthalpy and the equilibrium constant.

A
27
Q

What is Le Chatelier’s principle?

A

When a chemical system at equilibrium is disturbed, it reattains equilibrium by undergoing a net reaction that reduces the effects of the disturbance (change in concentration, temp, or pressure).

28
Q

When does K change?

A

K will only change when temp is changed

29
Q

For an endothermic reaction ________

A
  • Heat is a reactant
  • According to Le Châtelier’s principle, the equilibrium will shift away from the added heat.
  • Equilibrium constant increases if heat is added as a reactant
30
Q

What is the integrated Van’t Hoff equation?

A
31
Q

What is activity?

A

effective concentration or effective pressure and accounts for non-ideal behavior

32
Q

How do you define the reaction quotient in terms of activities?

A
33
Q

What happens to chemical potential under standard conditions?

A
  • Under standard concentrations the activity always equals 1 and ln(1)=0 so the concentration term disappears
34
Q

What is standard state for ideal gas?

A

The standard state for an ideal gas is the gas with a partial pressure equal to 1 bar.

35
Q

How does pressure relate to activity? (ideal gas)

A
36
Q

What is the equation for activity for real gases? What variable is required and what is it a function of?

A
37
Q

Describe the activity of a pure liquid or solid.

A

The Gibbs free energy of a solid or liquid does not change significantly with pressure. So for a pure solid or liquid at any pressure close to 1 bar:
A = 1

38
Q

How do you find activity for a component of a solution?

A

mole fraction (Xa) = (moles of species A)/(total moles in solution)

39
Q

How does the activity of a real solution compare to the activity of an ideal solution?

A

The activity of a real solution is lower than an ideal solution as concentration increases

40
Q

What do biochemical processes necessitate in relation to activity?

A
  • biochemical processes occur in very complex environments
  • biochemical processes occur at a pH of 7 and not a pH of 0 (1 M H+)
    -therefore Ah+ = 1 at a pH of 7
41
Q

What happens to H+ in the biochemical standard state?

A

activity of H+ = 1 and can be omitted from K

42
Q

What is activity?

A

Total concentration,
- In biological systems we often do not know the concentrations of related species
- Therefore, we define the activity of a molecule as the total concentration of all species of that molecule at pH 7:

43
Q

What is ionic strength?

A
44
Q

How does ionic strength relate to activity?

A

As the ionic strength of a solution increases, the activity coefficient (γ) of an ion decreases according to the Bebye-Huckel theory

45
Q

What is Debye-Huckel?

A
  • only applies to very dilute solutions (<10mM)
46
Q

How are activity coefficients treated in complex solutions?

A
47
Q

What problem arises with activity coefficients of ionic solutions?

A
  • For small uncharged molecules and low concentrations, we often assume an activity coefficient of unity.
  • For ions, even at low concentrations, this approximation is typically not valid.
  • However, ions always come in pairs (overall, a solution is electrically neutral).
  • Therefore, we cannot measure the activity coefficients of cations and anions separately.
  • We can only measure a mean activity coefficient.
48
Q

How do you calculate the chemical potential of an NaCl solution accounting for activity?

A
49
Q

Describe the activity coefficients of ions. What causes them to change?

A
  • Activity coefficients of ions strongly deviate from unity, even at moderate concentrations of ~0.1 M.
  • The activity coefficients are strongly dependent on the valency of the ion (the larger the valency, the higher the rate of decay of 𝛾_±).
50
Q

What does a positive or negative change in enthalpy imply about bond formation?

A

If more energy is produced in bond formation than that needed for bond breaking, the reaction is exothermic and the enthalpy is negative

51
Q

What is Vm?

A

molar volume

52
Q

Vm equations

A

∆Gm = Vm∆p
Vm = molar mass / density

53
Q

What does a change in enthalpy imply about bond formation?

A
  • negative change - bond formation
  • positive change - bond breaking
54
Q

What is the entropy of a process at constant pressure, temperature and surroundings?

A

Physical Chemistry (6 decks)

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