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CHEM/OCHEM (MCAT) > Thermodynamics and Kinetics > Flashcards

Thermodynamics and Kinetics Flashcards

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1
Q

Define thermodynamics.

A

study of the flow of energy during chemical processes

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2
Q

Define open system.

A

exchanges matter and energy with its surroundings

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3
Q

Define closed system.

A

exchanges ENERGY but NOT MATTER with its surroundings

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4
Q

Define isolated system.

A

exchanges NEITHER MATTER NOR ENERGY with its surroundings

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5
Q

What is an extensive property? Provide examples.

A

an extensive property depends on the amount of matter present in the system

e.g. mass, volume, internal energy, enthalpy, entropy, free energy, heat capacity

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6
Q

What is an intensive property? Provide some examples.

A

a property that does not depend on the amount of matter present in the system

e.g. temperature, density. melting point

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7
Q

In thermodynamics, what is the difference between a process and a path?

A

process = net difference between final and initial states

path = complete series of steps taken to get from the initial to the final state

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8
Q

What is the Zeroth Law?

A

if 2 systems are each in thermal equilibrium with a third system, they must all be in thermal equilibrium with each other

i. e. all 3 systems would be at the same temperature
e. g. if A and B are in equilibrium and B and C are in equilibrium, then A and C must also be in equilibrium

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9
Q

What is the difference between state function and path function?

A

state function = property that depends only on final and initial states (independent on path)

path function = property that depends on the way in which the change is carried out (dependent on path)

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10
Q

List some state functions.

A

energy
pressure
temperature
volume

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11
Q

List some path functions.

A

heat
work
distance
frequency

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12
Q

What are 6 types of internal energy? Define them

A

electronic energy = attraction between electrons and their nucleus
intermolecular potential energy = intermolecular forces
rest mass energy = mass and energy are theoretically interchangeable(E= mc^2)
vibrational energy = vibration of atoms around bonds
rotational energy = rotation of molecule around its centre of mass
translational energy =movement of the molecule

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13
Q

In the formula for pressure-volume work, what are the units of pressure?

W = -PdeltaV

A

P= kPa

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14
Q

Define internal energy.

A

sum of all the kinetic and potential energy in a system

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15
Q

What is the formula used to find internal energy?

A

delta E = E final - E initial

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16
Q

There are only 2 ways to transfer internal energy. What are they?

A

heat or work

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17
Q

What is the First Law of Thermodynamics? What is the resulting formula?

A

total energy of the system and the surroundings is CONSTANT–> energy change in system must equal sum of the heat exchanged to/from the system and the work done on/by the system

delta E = q+ W

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18
Q

What sign is given to endothermic processes?

a) (+)
b) (-)

A

a) (+)

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19
Q

What sign is given to exothermic processes?

a) (+)
b) (-)

A

b) (-)

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20
Q

Define enthalpy (H). What are the units? What is the formula?

A

total energy transferred during a chemical process, including the change in internal energy of the system (E) plus any energy (work) that is required to make room within the surroundings for the products of the rxn

units: Joule

delta H = delta E + W

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21
Q

Kinetic control leads to:

a) the “easiest” product
b) the most stable product

A

a) the “easiest” product

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22
Q

Thermodynamic control leads to:

a) the “easiest” product
b) the most stable product

A

b) the most stable product

23
Q

What is Hess’ Law?

A

total enthalpy of an overall reaction is equal to the sum of the enthalpy changes for the individual steps

delta H of reaction = sum of delta H

24
Q

What is the standard enthalpy of formation (delta Hf) of a pure element in its standard state?

A

zero

25
Q

What information does the thermodynamic quantity “entropy” (S) provide us with?

A

number of microstates (ways a system can exist) available to the system

26
Q

Delta S is POSITIVE when the number of microstates _________________.

a) decreases
b) increases
c) remains constant

A

b) increases

27
Q

Delta S is NEGATIVE when the number of microstates _________________.

a) decreases
b) increases
c) remains constant

A

a) decreases

28
Q

ice melting into water is an example of:

a) increasing entropy
b) decreasing entropy
c) constant entropy

A

a) increasing entropy

29
Q

steam condensing is an example of:

a) increasing entropy
b) decreasing entropy
c) constant entropy

A

b) decreasing entropy

30
Q

List the following in order of decreasing entropy:

liquid, solid, gas

A

gas&raquo_space;> liquid > solid

31
Q

TRUE or FALSE: a given substance is more entropic at lower temperature.

A

FALSE –> greater entropy at higher temperature (more kinetic energy and movement of particles, and more microstates)

32
Q

TRUE or FALSE: a sample of gas in a large volume is more entropic than it is in a small volume.

A

TRUE

33
Q

Fill in the blank with “smaller” or “larger”:

A ___________ molecule has a greater entropy than a ___________ molecule.

A

A LARGER molecule has a greater entropy than a SMALLER molecule.

34
Q

Fill in the blanks with either “reactants” or “products”:

An increase in the number of moles of gaseous ____________ compared to gaseous ____________ means an increase in entropy.

A

An increase in the number of moles of gaseous products compared to gaseous reactants means an increase in entropy.

35
Q

What is the second law of thermodynamics?

A

Any spontaneous process increase the entropy of the universe.

36
Q

What is the delta S (entropy) for a reversible process?

a) = 0
b) > 0
c) < 0

A

a) = 0

37
Q

What is the delta S (entropy) for an irreversible, spontaneous process?

a) = 0
b) > 0
c) < 0

A

b) > 0

38
Q

What is the Third Law of Thermodynamics?

A

The entropy of a perfect crystal at 0K is zero. (no motion, no disorder)

39
Q

What are the 3 laws of thermodynamics?

A

First Law: Total energy of the system and the surroundings is CONSTANT.

Second Law: Any spontaneous process INCREASE THE ENTROPY of the universe.

Third Law: The entropy of a perfect crystal at 0K is zero. (no motion, no disorder)

40
Q

The fact that the system and the surroundings cannot be returned to their previous condition indicates that the original process must have been:

a) spontaneous
b) reversible
c) irreversible
d) endothermic
e) exothermic

(Select all that apply.)

A

a) spontaneous

c) irreversible

41
Q

When the change in free energy (delta G) is NEGATIVE, the reaction is ____________ in the direction written.

a) spontaneous
b) non-spontaneous

A

a) spontaneous

42
Q

When the change in free energy (delta G) is POSITIVE, the reaction is ____________ in the direction written.

a) spontaneous
b) non-spontaneous

A

b) non-spontaneous

note: it is spontaneous in the OPPOSITE direction that it is written

43
Q

If the equilibrium constant for a forward reaction is Kc = [A][B]/[C] what is the equilibrium constant for the reverse reaction?

A

Kc of reverse reaction = 1/Kc of forward reaction = [C]/[A][B]

(i.e. Kc of reverse rxn is the inverse of the Kc of forward rxn)

44
Q

If Q < K:

a) the forward reaction is being favoured
b) the reverse reaction is being favoured
c) the system is at equilibrium

note: Q = reaction quotient; K = equilibrium constant

A

a) forward reaction is being favoured
explanation: since there is less product (Q) than at equilibrium, then more product needs to be made to reach equilibrium…therefore, forward reaction favoured

45
Q

If Q > K:

a) the forward reaction is being favoured
b) the reverse reaction is being favoured
c) the system is at equilibrium

note: Q = reaction quotient; K = equilibrium constant

A

b) the reverse reaction is being favoured
explanation: since there is more product (Q) than at equilibrium, then less product needs to be made to reach equilibrium…therefore, reverse reaction favoured

46
Q

If Q = K:

a) the forward reaction is being favoured
b) the reverse reaction is being favoured
c) the system is at equilibrium

note: Q = reaction quotient; K = equilibrium constant

A

c) the system is at equilibrium

47
Q

What is Le Chatelier’s Principle?

A

When a system is disturbed from a state of equilibrium, it will SHIFT the position of equilibrium in the direction that REDUCES the effect of the disturbance.

48
Q

TRUE or FALSE: Changes in volume and pressure for gases changes the value of k (equilibrium constant).

A

FALSE –> change in V or P for gases does not affect value of k

49
Q

What do the concentration-time graphs look like for 0th, 1st, and 2nd order reactions? Draw the graphs?

A

See page 258 in chem cc.

50
Q

The transition state complex (activated complex) is the most ______a/b_______ in the reaction pathway. It appears at the _____c/d_____ point on the reaction pathway vs. energy graph.

a) stable
b) unstable

c) lowest
d) highest

A

b) unstable

d) highest

51
Q

What is a reaction profile?

A

a plot of energy (y-axis) vs. progress of reaction (x-axis)

52
Q

TRUE or FALSE: In general, if you increase the temperature of a reaction, you decrease the rate of the reaction.

A

FALSE –> increase temperature, increase rate

53
Q

What is the rate-determining step of a reaction?

a) fastest step
b) slowest step

A

b) slowest step

CHEM/OCHEM (MCAT) (10 decks)

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