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MCAT General Chemistry > Ch 7 - Thermochemistry > Flashcards

Ch 7 - Thermochemistry Flashcards

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1
Q

How are systems classified?

A

based on what is or is not exchanged with the surroundings

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2
Q

What is the difference between an isolated, closed, and open system?

A
  • isolate: exchange neither matter nor energy with the environment
  • closed: can exchange energy but not matter with the environment
  • open: can exchange both energy and matter with the environment
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3
Q

How are processes categorized?

A

based on a single constant property

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4
Q

What is the difference between isothermal, adiabatic, isobaric, and isovolumetric processes?

A
  • isothermal: occur at constant temperature (U = 0, Q = W)
  • adiabatic: exchange no heat with the environment (Q = 0, U = -W)
  • isobaric: occur at constant pressure (flat line in PV graph)
  • isovolumetric (isochoric) occur at constant volume (W = 0, U = Q)
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5
Q

What are state functions?

A
  • describe the physical properties of an equilibrium state
    TV HUGS
  • they are pathway independent and include pressure, density, temperature, volume, enthalpy, internal energy, Gibbs free energy, and entropy
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6
Q

What are standard conditions?

A

defined as 298 K, 1 atm, and 1 M concentration

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7
Q

What is the standard state and what functions are calculate in this state?

A
  • most prevalent form under standard conditions

- standard enthalpy, entropy, and free energy

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8
Q

Where do phase changes exist?

A

at characteristic temperatures and pressures

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9
Q

When do fusion and freezing occur?

A

fusion (meltion) and freeing (crystallization and solidification) occur at the boundary between the solid and liquid phases

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10
Q

When to vaporization and condensation occur?

A

vaporization (evaporation or boiling) and condensation occur at the boundary between liquid and gas phase

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11
Q

When do sublimation and deposition occur?

A

at the boundary between solid and gas phase

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12
Q

What happens at temperatures above the critical point?

A

the liquid and gas phase are indistinguishable and the heat of vaporization is 0

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13
Q

What happens at the triple point?

A

all 3 phases of matter exist in equilibrium

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14
Q

What does the phase diagram graph?

A

the phases and phase equilibrium as a function of temperature and pressure

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15
Q

What is the difference between heat and temperature?

A
  • temperature: scaled measure of the average kinetic energy of a substance
  • heat: transfer of energy that results from differences of temperature between 2 substances
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16
Q

How can you calculate the heat content of a system undergoing heating, cooling, or phase changes?

A

sum of all the respective energy changes

17
Q

What is enthalpy?

A

a measure of the potential energy of a system found in intermolecular attractions and chemical bonds
Hrxn = Hproducts - Hreactants

18
Q

What is Hess’s law?

A

states that the total change in potential energy of a system is equal to the changes of potential energies of the individual steps of the process

19
Q

How is enthalpy calculated?

A

using heats of formation, heats of combustion, or bond dissociation energies

20
Q

What is entropy and how is it calculated?

A

a measure of the degree to which energy has been spread throughout the system or between a system and its surroundings
change in S = Qrev/T

21
Q

When is entropy maximized?

A

at equilibrium

22
Q

What is entropy a ratio of?

A

heat transferred per mole per unit kelvin

23
Q

What is Gibbs free energy derived from?

A

both enthalpy and entropy values for a given system

change in G = chang in H -TchangeS

24
Q

What does the change in Gibbs free energy determines?

A

whether a process is spontaneous or nonspontaneous

  • < 0: rxn proceeds forward (spontaneous)
  • = 0: rxn in dynamic equilibrium
  • > 0: rxn processed in reverse (nonspontaneous)
25
Q

What does Gibbs free energy depend on?

A

temperature,

- temperature-dependent processes change between spontaneous and nonspontaneous, depending on temperature

26
Q

What is the difference between calculating heat transfer when there is or is not a phase change?

A
  • no phase change: q = mcAT

- during phase change: q = mL

27
Q

What is the first law of thermodynamics equation?

A

change in U = Q - W

28
Q

How is standard enthalpy calculated?

A

Hrxn0 = sum of Hf,products - sum of Hf,reactants

29
Q

How is bond enthalpy calcualted?

A

Hrx0 = sum of Hbonds broken - sum of H bonds formed

= total energy absorbed - total energy released

30
Q

What is the second law of thermodynamics equation?

A

change Suniverse = change Ssystem + change S surroundings > 0

31
Q

How is standard Gibbs free energy from equilibrium constant calculated?

A

change in Grxn0 = -RTlnKeq

32
Q

How is Gibbs free energy from reaction quotient calcualted?

A

change in Grxn = change in Grxn0 + RTlnQ = RTln(Q/Keq)

33
Q

What are process functinons?

A

path between equilibrium states

- Q (heat), W (work)

34
Q

What is the difference between specific heat and heat capacity?

A
  • specific heat (c): energy required to raise the temperature of one gram of a substance by 1 C
  • heat capacity (mc): product of mass and specific heat and is the energy required to raise any given amount of substance by 1 C
35
Q

What is the difference between constant-volume and constant-pressure calorimetry?

A
  • constant pressure (coffee cup) is exposed to constant (atmospheric) pressure; as the rxn proceeds, the temperature of the contents is measure to determine the heat of the rxn
  • constant volume (bomb): heat of certain rxns (like combustion) can be measured indirectly by assessing temperature change in a water bath around the reaction vessel
36
Q

What is the difference between endothermic and exothermic process?

A
  • endo: involve an increase in heat content of a system from the surroundings (change in H > 0)
  • exo: a release of heat content from a system (change in H < 0)
37
Q

Which combustion reactions will have the most exothermic standard heat of combustion?

A
  • combustion often involves the reaction of a hydrocarbon with oxygen to produce CO2 and H2O
  • longer hydrocarbon chains yield greater amounts of combustion products and release more heat in the process
38
Q

What relationship is required between Q and Keq in order for a reaction to be spontaneous?

A

Keq > Q

MCAT General Chemistry (12 decks)

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