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MCAT Chem > Chem #7 > Flashcards

Chem #7 Flashcards

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1
Q

system

A

the matter that is being observed—the total amount of reactants and products in a chemical reaction.

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2
Q

surroundings

A

Surroundings (environment): everything outside of the system

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3
Q

isolated system

A

The system cannot exchange energy (heat and work) or matter with the surroundings; for example, an insulated bomb calorimeter.

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4
Q

closed system

A

the system can exchange energy (heat and work) but not matter with the surroundings; for example, a steam radiator.

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5
Q

open system

A

the system can exchange both energy (heat and work) and matter with the surroundings; for example, a pot of boiling water

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6
Q

process

A

when a system experiences a change in one or more of its properties (such as concentrations of reactants or products, temperature, or pressure)

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7
Q

isothermal process

A

occur when the system’s temperature is constant

 Constant temperature implies that the total energy of the system (U) is constant (delta U = 0).

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8
Q

adiabatic process

A

occur when no heat is exchanged between the system and the environment.

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9
Q

isobaric process

A

occur when the pressure of the system is constant.

 Does not alter the first law but appears as a straight line on the P-V graph.

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10
Q

isochoric

A

experience no change in volume

 Vertical line on the P-V graph, work = 0.

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11
Q

spontaneous process

A

one that can occur by itself without having to be driven by energy from an outside source.
 Spontaneous processes can sometimes be VERY slow.

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12
Q

coupling

A

a common method for supplying energy for nonspontaneous reactions.
• Ex: The combustion of glucose is exergonic; the formation of peptide bonds is endergonic. Energy from combustion of glucose can be stored in the bonds in GTP, which are then lysed to provide the energy for forming peptide bonds.

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13
Q

state functions

A

describe the system in an equilibrium state. They cannot describe the process of the system. Useful for comparing one equilibrium state to another.
o Pressure, density, temperature, volume, enthalpy, internal energy, Gibbs free energy, entropy
o Independent of the path (process) taken, but are not necessarily independent of each other

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14
Q

process functions

A 
the pathway taken from one equilibrium state to another 
o	Work (W) and heat (Q) are the most important ones.
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15
Q

state functions only depend on _____

A

the differences between the final and initial states, not how you get there.

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16
Q

standard conditions

A

defined because systems can be in different equilibrium states at different temperatures and pressure (for measuring the enthalpy, entropy, and Gibbs free energy changes in a reaction).
o 298 K, 1 atm pressure, 1 M concentrations.
o Used for kinetics, equilibrium, and thermodynamics.

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17
Q

standard conditions versus standard temperature and pressure (STP)

A

STP used for ideal gas law and is 273 K, 1 atm

standard conditions is 298 K, 1 atm, 1 M, and is used for kinetics, equilibrium, and thermodynamics.

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18
Q

standard state

A

the most stable form of a substance.

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19
Q

Standard enthalpy, standard entropy, and standard free energy changes

A

the changes that occur when a reaction takes place under standard conditions

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20
Q

process going solid to liquid

A

melting, fusion

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21
Q

process going liquid to gas

A

evaporation, vaporization
: when some of the liquid molecules near the surface have enough kinetic energy to leave the liquid phase and escape into the gaseous phase.
• Endothermic process for which the heat source is the liquid water.
• Each time the liquid loses a high-energy particle, the temperature of the remaining liquid decreases.

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22
Q

process going gas to liquid

A

condensation
: gases returning to the liquid phase.
• Facilitated by lower pressure or higher temperature.
• Vapor pressure of the liquid: the pressure that the gas exerts over the liquid at equilibrium.
• Boiling point: the temperature at which the vapor pressure of the liquid equals the ambient (external, applied, or incident) pressure

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23
Q

process going liquid to solid

A

freezing/solidification/crystallization

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24
Q

process going gas to solid

A

deposition

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25
Q

process going solid to gas

A

sublimation

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26
Q

what is occuring during sweating

A

sweating (vaporization) is an endothermic reaction as energy is required for liquid to vaporize into gas which removes heat from the body

blood vessels vasodilate to get more heat release.

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27
Q

phase diagrams

A

graphs that show the standard and nonstandard states of matter for a given substance in an isolated system, as determined by temperatures and pressures.
 Graphs that show the temperatures and pressures at which a substance will be thermodynamically stable in a particular phase.
• Also show temps and pressures at which phases will be in equilibrium.

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28
Q

triple point

A

all 3 phases are in
equilibrium

the point at which the three phase boundaries meet. The temperature and pressure at which the three phases exist in equilibrium.

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29
Q

critical point

A

where the phase boundary between the gas and liquid phases terminates.
• This is the temperature and pressure at which there is no distinction between the phases.
o Supercritical fluids
o The heat of vaporization at this point and for all temperatures and pressures above the critical point is zero.

ABOVE WHICH THE HEAT OF VAPORIZATION IS 0

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30
Q

phase changes

A

: (solid = liquid = gas) are reversible, and an equilibrium of phases will eventually be reached at any given combination of temperature and pressure.
 Ice to water and water to ice at the same time.
 Phase equilibria: analogous to dynamic equilibria of reversible chemical reactions (concentrations remain the same because the forward and reverse reactions are equal).

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31
Q

The temperature of any substance in any phase is related to the _____ of the molecules that make up the substance.

A

average kinetic energy

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32
Q

boiling point

A

a specific type of vaporization that occurs only under certain conditions. Boiling is the rapid bubbling of the entire liquid with rapid release of the liquid as gas particles.
Only occurs above the boiling point of the liquid and involves vaporization through the entire volume of the liquid.
the temperature at which the vapor pressure of the liquid equals the ambient (external, applied, incident) pressure

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33
Q

what point does the boiling point occur at?

A

the temperature at which the vapor pressure of the liquid equals the ambient (external, applied, or incident) pressure

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34
Q

 The availability of energy _____ (specific way in which the energy of a system can be organized) increases as the temperature of the solid increases.

A

microstates

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35
Q

draw a graph representing heat added and temperature

A

plateaus and inclines

plateau is a phase change

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36
Q

temperature

A

related to the average kinetic energy of particle of a substance.
 The average kinetic energy of the particles in a substance is related to the thermal energy (Enthalpy) of the substance.

37
Q

heat

A

a specific form of energy that can enter or leave a system. The transfer of energy from one substance to another as a result of their differences in temperature.
 Zeroth law of thermodynamics: objects are in thermal equilibrium only when their temperatures are equal.
 Process function

38
Q

sign for a system absorbing heat

A

+

39
Q

sign for a system releasing heat

A

_

40
Q

exothermic

A

the system releases heat

41
Q

endothermic

A

the system absorbs heat

42
Q

under constant pressure, relate q and enthalpy

A

equal

43
Q

calorimetry

A

the process of measuring transferred heat

44
Q

calorimetry: constant pressure

A

coffee cup calorimeter
 Imagine a coffee cup that is sealed and there is reduced loss of heat to the environment. The temperature can be measured as the reaction progresses. The constant pressure is atmospheric pressure.

45
Q

calorimetry: constant volume

A 
bomb calorimeter (decomposition vessel)
	Sample in oxygen container submerged in water. 
	Wcalorimeter = 0.
46
Q

bomb calorimeter

A

constant volume

47
Q

coffee cup calorimeter

A

constant pressure

48
Q

specific heat

A

the amount of energy required to raise the temperature of one gram of a substance by one degree Celsius (or K)
o Of H2O (l): 1 cal / (g)(K)
o Heat capacity: mass x specific heat

49
Q

relate specific heat and heat capacity

A

mass x specific heat = heat capacity

50
Q

discuss a heating curve

A

o Compound is heated to melting or boiling point, stays here a little until all of the sample changes phase, then the temperature will begin to rise again.
o When transitioning at the solid-liquid boundary, the enthalpy of fusion (ΔHfus) must be used.
 Solid to liquid: it is positive cause heat must be added
o When transitioning at the liquid-gas boundary, the enthalpy of vaporization (ΔHvap) must be used
 Liquid to gas: it is positive cause heat must be added
o Latent heat: enthalpy of an isothermal process
o Add up the heats for different steps.

51
Q

can you have heat being added to an isothermal process?

A

YES

phase boundary and latent heat on heating curve

52
Q

enthalpy

A

(H): used to express heat changes at constant pressure.
o State function
o Change in enthalpy is equal to the heat transferred into or out of the system at constant pressure
o Only ΔH can be calculated, not regular H.

53
Q

standard enthalpy of formation

A

formation (ΔH°f): enthalpy required to produce one mole of a compound from its elements in their standard states.
o Standard state is 298 L and 1 atm.
o ΔH°f of an element in its standard state is 0.

54
Q

Standard enthalpy of reaction (ΔH°rxn):

A

the enthalpy change accompanying a reaction being carried out under standard conditions.
o Sum of product standard heats of formation minus reactant standard heats of formation

55
Q

Hess’s law

A

the enthalpy changes of reactions are additive.
o Enthalpy is a state function so as long as you go from reactants to products it does not matter how you get there, the enthalpy change will still be the same.
o Applies to ANY state function, path independent.

56
Q

Bond formation is typically ____while bond breaking is typically _____

A

exothermic
endothermic

Exceptions in biology: ATP: bond breaking is exothermic

57
Q

Bond enthalpies (bond dissociation energies):

A

the average energy that is required to break a particular type of bond between atoms in the gas phase. (kJ/mol of bonds broken)
• Does not matter if an element is in its standard state here or not, still add up all of the bond energies.

58
Q

standard heat of combustion

A 
the enthalpy change associated with the combustion of a fuel. 
•	Typical combustion reactions:
o	Hydrocarbon with H2
o	H2g and Cl2g  HClg
o	F2 is the oxidant
59
Q

second law of thermodynamics

A

energy spontaneously disperse from being localized to becoming spread out if it is not hindered from doing so.
o The entropy of the universe is increasing.

60
Q

entropy

A

the measure of the spontaneous dispersal of energy at a specific temperature: how much energy is spread out and how widely is it spread out.
o When energy is distributed into a system, its entropy increases.
o Pathway independent.
o + entropy, more disorder.
o Heat pack on a wound  dispersal of energy

61
Q

when is deltaG temperature dependent?

A

ΔG is temperature dependent when ΔH and ΔS have the same sign.

62
Q

standard free energy ΔG°rxn

A

): the free energy change of reactions can be measured under standard state conditions.
o ΔG°f: the standard free energy of formation of a compound is the free energy change that occurs when 1 mole of a compound in its standard state is produced from its respective elements in their standard states under standard state conditions.
 Any element is 0.

63
Q

what is the first law of thermodynamics and how are things defined?

A

deltaU = q + w

q and w are heat and work done on the system, respectively.

64
Q

condensation is facilitated by a ___ temperature or a ____ pressure

A

low

high

65
Q

vapor pressure is _____

A

the pressure that a gas exerts over a liquid at equilibrium (it is the vapor pressure OF THE LIQUID)

66
Q

process of going solid to liquid

A

melting or fusion

67
Q

the solid phase of a substance is often found at ____ temperatures and ____ pressures

A

low

high

68
Q

the base boundary that separates the solid and liquid _____ while the phase boundary that separates the liquid and gas _____

A

extends forever

terminates at the critical point

69
Q

a negative slope in a phase diagram for the liquid and solid boundary means that ____

A

the liquid is more dense than the solid

increasing pressure with constant temperature results in melting.

70
Q

____ is a specific form of energy that can leave or enter a system while ____ is a measure of the average kinetic energy of the particles in a system

A

heat

temperature

71
Q

1 cal = ___ J

A

4.184 J

72
Q

Enthalpy is equivalent to heat under constant ____

A

pressure

73
Q

what is another word for bomb calorimeter

A

decomposition vessel

74
Q

on a heating curve, you use the _____ when transitioning from solid to liquid (or vice versa) and you use _____ when transitioning from liquid to gas (and vice versa)

A

enthalpy/heat of fusion

enthalpy/heat of vaporization

75
Q

what is latent heat used for and what is its units

A

used for calculating heat added in an isothermal process (heat curve)
units: cal/g

76
Q

what are the heat capacities for water (solid, liquid, gas)

A

s: 2.18 J/gK
l: 4.18 J/gK
g: 2 J/gK

77
Q

a coffee cup calorimeter is exposed to constant pressure from what

A

the environment

78
Q

the standard enthalpy of formation of an element in its standard state is ____

A

0

79
Q

As compared to Keq values, in Hesses law you can ______ enthalpies

A

add, multiply by coefficients, negative if reverse (same for entropy and Gibbs free energy)

for K values in equilibrium you multiply them for combining reactions, raise to the power for adding coefficients, and take inverse if doing reverse reaction.

80
Q

bond breaking is ____ while bond forming is _____

A

endothermic

exothermic

81
Q

Can combustion reactions occur without O2?

A

Yes, Ex: Fluorine as oxidant

82
Q

what are the units of entropy?

A

J/(mol)(K)

83
Q

the energy of the universe _____ reduced spontaneously

A

can never be

84
Q

the change in free energy is the _______ released by a process, occurring at _______, that is available to perform ______

A

maximum amount of energy
constant temperature and pressure
useful work

85
Q

deltaG is temperature dependent when deltaS and delta H ____

A

have the same sign

86
Q

when water’s vapor pressure equals the ambient pressure, this is known as the ____

A

boiling point

87
Q

entropy is maximized at _____

A

equilibrium

88
Q

longer hydrocarbon chains yield ____ amounts of combustion products and release ___ heat

A

greater

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MCAT Chem (12 decks)

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