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MCAT Chemistry > Thermochemistry > Flashcards

Thermochemistry Flashcards

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1
Q

First law of thermodynamics

A

Change in internal energy (delta U) = Heat (Q) - Work (W)

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2
Q

Adiabatic process

A

No heat exchange

Delta U = -W

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3
Q

Isothermic process

A

Constant temperature

Delta U = 0 –> Q = W

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4
Q

Isobaric process

A

Constant pressure

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5
Q

Isochoric process

A

Constant volume

Delta U = Q

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6
Q

What are two process functions?

A

Heat (Q) and work (W)

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7
Q

1 cal = ? J

A

4200 J

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8
Q

When is enthalpy (delta H) = Q?

A

At constant pressure

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9
Q

Heat absorbed or released in a given process = ?

A

q = m.c.delta T

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10
Q

What is the specific heat of water?

A

1

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11
Q

Heat capacity = ?

A

m.c

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12
Q

Equation when using a bomb calorimeter?

A

q sample + q oxygen = (-) q surroundings (water)

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13
Q

Equation to use to find equilibrium temperature of two objects?

A

q hot = (-) q cold

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14
Q

Heat of phase change = ?

A

q = m. L (latent heat)

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15
Q

What is held constant in a bomb calorimeter?

A

Volume

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16
Q

What is held constant in a coffee-cup calorimeter?

A

Pressure

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17
Q

Enthalpy (Delta H) = ?
(-) ?
(+) ?

A

Heat transferred into or out of the system
(-) : exothermic
(+) : endothermic

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18
Q

What is the standard enthalpy of formation, DeltaHf?

A

Enthalpy required to produce one mole of a compound from its elements in their standard states.

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19
Q

What is the standard heat of a reaction equal to?

A

Delta Hrxn = Sum of Delta Hf products - Sum of Delta Hf reactants

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20
Q

What is Hess’ law?

A

Delta H = Delta H1 + Delta H2 + Delta H3 …

It works for all other state functions as well.

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21
Q

What is the bond dissociation energy?

A

Average energy required to break a particular type of bond between atoms in the gas phase

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22
Q

Equation for Gibbs free energy? Mnemonic with the fish!!

A

Delta G = Delta H - T. Delta S

Goldfish are horrible without tartare sauce

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23
Q

What is an exergonic reaction? What is Delta G?

A

Spontaneous: Delta G (-)

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24
Q

What is an endergonic reaction? What is Delta G?

A

Nonspontaneous: Delta G (+)

25
Q

When is Delta G temperature dependent?

A

When Delta S and Delta H have the same sign

26
Q

What is the standard gibbs free energy?

A

Delta Grxn = Sum of Delta G products - Sum of Delta G reactants

27
Q

How to calculate the standard Delta Grxn from Keq?

A

Standard Delta G rxn = - RT ln. Keq

28
Q

How to calculate the Delta Grxn from Keq and Q? How to estimate the sign of Delta Grxn?

A

Delta G rxn = RT ln (Q/Keq) = Delta G (standard) + RT.lnQ

If Q/Keq

29
Q

What happens to the volume of a substance as it goes from solid to liquid? Why? What is the exception to this rule?

A

It increases because it becomes less dense

Water

30
Q

How can the entropy change in a reaction be estimated? 2 factors

A
  1. number of moles of reactants and products:
    a. decrease in moles = decrease in entropy
    b. increase in moles = increase in entropy
  2. phase changes
    a. gas to solid = decrease in entropy
    b. solid to liquid = increase in entropy
31
Q

Are explosions spontaneous or nonspontaneous?

A

Spontaneous

32
Q

What is the enthalpy of formation of an element?

A

Always 0

33
Q

Which side of an exothermic reaction is favored at high temperatures?

A

Shift to the left!

34
Q

How to apply Hess’ law to heats of combustion and heats of formation?

A

Heat of combustion = sum of the heat of formation of the products - heat of formation of the reactants

35
Q

What is the heat of formation of O2?

A

0

36
Q

What does the standard heat of formation represent?

A

The heat necessary to synthesize elements in their standard state

37
Q

What unit to use for all of these equations?

A

Kelvin!

38
Q

When asked which conditions are favorable to a certain reactions, what are the 2 things you should check?

A

Moles of gas

Exo or endothermic?

39
Q

What is the equation to calculate entropy?

A

Delta S = Qrev / T

Qrev = heat gained or lost in a reversible reaction
T = temperature
40
Q

When energy is added to a system, does its entropy increase or decrease?

A

Increase

41
Q

When energy is removed from a system, does its entropy increase or decrease?

A

Decrease

42
Q

How to calculate the change in entropy of a system?

A

Add up the change in entropy of the different elements in the system

43
Q

What is the work of a calorimeter equal to?

A

0

44
Q

What is the effect on entropy when particles move from high concentration to low concentration?

A

Increase in entropy

45
Q

If Delta G is (-), then what does this mean for Q?

A

Q is smaller than Keq

46
Q

What does a negative change in entropy mean?

A

It decreases

47
Q

Solvation layer formation effects on entropy? Free energy?

A

Entropy: decrease

Free energy is > 0 –> non spontaneous

48
Q

What is favorable: increasing or decreasing entropy?

A

Increasing

49
Q

When adding hydrophilic molecules to water, is entropy increased or decreased? How is free energy affected?

A

Increased

Free energy spontaneous

50
Q

What is the Delta G of passive transport?

A

(-)

51
Q

What is the Delta G of active transport?

A

(+)

52
Q

What is Delta G standard ‘ ?

A

Standardized for neutral pH = 7

53
Q

What is the pH for standard Delta G?

A

0

54
Q

How can I use the first law of thermodynamics in the cellular environment?

A

Fixed volume and pressure, so Delta U = Q

55
Q

What is the equation for the entropy of the universe? What does it mean?

A

Delta Suniv = Delta S system + Delta S surroundings > 0
Which means: the entropy of a system and its surroundings will NEVER decrease, it will always remain 0 or increase
At constant P and T, the entropy of a system will spontaneously increase

56
Q

What does it mean in radioactive decay if there is no tissue damage?

A

There was no gamma emission

57
Q

When does “all” of a sample is considered to have decayed?

A

7-8 half lives

58
Q

Which nuclear decay can be detected on an atomic absorption spectrum?

A

Gamma radiation

MCAT Chemistry (17 decks)

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