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Chemistry > Thermochemistry > Flashcards

Thermochemistry Flashcards

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1
Q

System

A

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

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2
Q

Surroundings/Enviornment

A

everything out side the system

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3
Q

If we are looking at the coffee as the system and the cup as the enviornment, what heat transfer are we studying?

A

Heat transfer between coffee and the cup

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4
Q

Isolated System

A

Environment and System do not exchange energy (heat/work) or matter

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5
Q

Closed System

A

System and Environment exchange energy but not matter

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6
Q

Open System

A

system and environment exchange both energy and matter

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7
Q

First Law of Thermodynamics

A

change in internal energy of a system is equal to the sum of heat added to the system minus work done by the system

U = Q - W

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8
Q

Isothermal Process

A

temperature is constant

Internal energy, U, is constant = 0

Work done by system = heat added to the system

Q = W

hyperbolic

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9
Q

Adiabatic Process

A

No heat exchange; Q = 0

change in internal energy of the system is opposite of work done by system

U = -W

extremely hyperbolic

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10
Q

Isobaric Process

A

Pressure is constant

no affect on first law

flat line

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11
Q

Isovolumetric/Isochoric Process

A

Volume is constant

no work is performed ; W = 0

change in energy is equal to energy placed into the system

U = Q

vertical line

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12
Q

Spontaneous Process

A

occurs by itself without having to be driven by energy from an outside source

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13
Q

State Functions

A

pressure, density, temperature, volume, enthalpy, internal energy, gibbs free energy, entropy

when the state of a system changes, one or more of these will change

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14
Q

Standard Conditions

A

298k

1 atm

1 M

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15
Q

Phase Changes

A

are reversible, and an equilibrium of phases will be given for a combination of temperature and pressure

ex: 0 degrees C and 1 atm pressure ic e and water are at equilibrium soice absorbs heat to become water but the water lsoes heat and becomes ice keeping relatively equal amounts

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16
Q

Phase equilibrium are analogous to the dynamic equilibrium of _________: the concentration of reactants and products are constant because the rates ____ and _____ are equal.

A

reversible chemical reactions

forward

reverse reactions

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17
Q

Not all molecules possess the same instantaneous speeds, meaning not the same instantaneous kinetic energy values. In the liquid phase, the molecules near the surface of the liquid have _________ to leave the liquid phase and enter the ______. This is known as _______.

A

enough kinetic energy

gas

evaporation/vaporization

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18
Q

Evaporation is an ________ process where the heat source is ______

A

endothermic process

liquid water

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19
Q

Boiling

A

a specific type of vaporization where the entire liquid bubbles and there is rapid release of liquid to gas particles once the BP is met

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20
Q

Condensation

A

gas molecules forced back to liquid molecules based on pressure or low temperature

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21
Q

Vapor Pressure

A

pressure exerted on the liquid by the gas

increases as temperature increases because mroe liquid particles can escape into gas

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22
Q

Boiling point

A

where vapor pressure is equal to the ambient/applied pressure

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23
Q

Whereas pure crystalline solids have ditinct _______, amorphous solids like glass, plastix, chocolate _______ over a _______ of temperatures due to their less ordered molecular structure

A

melting points

melt/solidify

range

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24
Q

Sublimation

A

solid to gas directly

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25
Q

Deposition

A

gas to solid directly

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26
Q

Triple Point

A

temperature and pressure where all 3 phases are in equilibria

27
Q

Critical Point

A

between liquid and gas phase where there is no distinction between liquid and gas

called supercritical fluids

density of liquid and gas are equal

28
Q

Temperature

A

avg kinetic energy of particles in a substance

29
Q

Enthalpy (Thermal ENergy)

A

heat under constant pressure

30
Q

Heat

A

transfer of energy from one substance to another resulting from a difference in temperatures

31
Q

Endothermic

A

process where system absorbs heat

delta Q > 0

32
Q

Exothermic

A

process where system releases heat

delta Q < 0

33
Q

q = mcdeltaT

A

m = mass

c = specific heat of substance

q = heat absorbed or released

34
Q

Specific Heat

A

amount of energy required to raise the temperature of one gram of substance by one degree Celsius/Kelvin

35
Q

Heat capacities

A

reason why it is less heat to raise temp of glass of water than a pool

= mass * specific heat

36
Q

Constant Pressure Calorimeter

A

incident pressure (atmospheric pressure) is e kept constant

temperature is measured as reaction progresses with no gain/loss of heat to the environment

37
Q

Constant Volume Calorimetry

A

no work is done as W = p* delta V

no heat is exchanged between the calorimeter and universe so Q calorimeter is 0

deltaUsys + deltaUsurr = deltaU cal = Q - W = 0

delta U sys = - delta U surr

qsys = -qsurroundings

38
Q

Heating Curves

A

When a compound is ehated, temperature rises until the melting/boiling point is reached.

Here temp stays constant until all of the sample is converted to the next phase and then temp begins to rise again

39
Q

When phase changes occur, the heat added does not change the _____ but is used to _____

A

temperature

overcome the attractive forces holding the phase

40
Q

Enthalpy of Fusion (latent heat of Fusion)

A

transition during solid-liquid boundary

determines the heat transferred during phase change

+ when going from solid to liquid as heat is added

  • when going from liquid to solid as heat must be removed
41
Q

Enthalpy of Vaporization (latent heat of vaporization)

A

transition during liquid-solid boundary

determines the heat transferred during phase change

+ when going fromn liquid to gas as heat is added

  • when going from gas to liquid as heat is lost
42
Q

q = mL

A

m = mass

L - latent heat, enthalpy essentially of the process

43
Q

The total amount of heat needed to cross multiple phase boundriesis a _____ of the heats for changing the temperature of each of the respective phases and the heats associated with phase changes.

A

summation

ex: energy required to make ice cube melt at 40 degrees

q1 = heating to the transition temperature (q=mcdeltaT)

q2 = heat generated during phase change (q=mL)

q3 = heat generated to a temperature(q=mcdeltaT)

44
Q

Enthalpy Change of a Reaction

A

deltaH reaction = Hproducts - Hreactants

+ = endothermic process

  • = exothermic process
45
Q

Enthalpy cannot be measured, only _______

A

deltaH

46
Q

Standard Enthalpy of Formation (deltaHf)

A

enthalpy required to produce one mole of a compound from its elements in standard state

47
Q

Standard Heat of a Reaction (deltaHrxn)

A

enthalpy change accompanying a reaction being carried out under standard conditions

deltaHrxn = sum( deltaHf,prod ) - sum(deltaHf,react)

48
Q

Hess’s Law

A

states that enthalpy changes of reactions are additive

deltaHrxn = deltaH(reactants->elements) + deltaH(elements->products)

remember to add the deltaHrxns together and flip sign if flipping direction of the reaction (even multiply if need to)

arrange to cross out uncessary atoms/elements

49
Q

Bond Dissociation Energy

A

average energy required to break a particular type of bond between atoms in the gas phase (endothermic reaction

50
Q

Bond breaking has the same enthalpy as bond formation but is _____

A

opposite

51
Q

Standard Heat of Combustion (delta H combo)

A

enthalpy change associated with the combustion of a fuel

52
Q

Second Law of Thermodynamics

A

energy is spontaneously dispered from being localized to becoming spread out when not hindered

53
Q

Entropy

A

how spontaneous the dispersion of energy at a temperature is

deltaS = Qrev/T

Q rev = heat gained/lost in a reversible process

delta S of products and reactants can be used to find deltaSrxn like entropy (products - reactants)

54
Q

When energy is distributed into a system at a given temperature, its entropy _____ . When energy is distributed out of a system, its entropy _____ .

A

increases

decreases

55
Q

Gibbs Free Energy

A

measure of the change in enthalpy and entropy as a system undergoes a process

tells if a reaction is spontaneous or not

deltaG = deltaH - T*deltaS

T*deltaS represents the total amount of energy absorbed by a system when its entropy increases reversibly

56
Q

Movement towards the equilibrium position is a _____ in Gibbs Free Energy (G <0) and is ______. The reaction RELEASES energy and is called ________.

Movement away from the equilibrium position is an ____ in Gibbs free energy (G > 0) and is _______. The reaction is ___ and ABSORBS energy.

A

decrease, spontaneous, exergonic

increase, nonspontaneous, endergonic

57
Q

At equilibrium, deltaG is ______ and deltaH = T*deltaS

A

0

58
Q 
delta H         delta S
\+                         +
\+                        -
-                         +
-                         -
A

1) spontaneous at HIGH Temperature
2) nonspontaneous always
3) spontaneous always
4) spontaneous at low temperature

59
Q

Remember, rate of a reaction is dependent on Ea, _______, not delta G

A

activation energy

60
Q

When a reaction occurs with a Kinetic and Thermodynamic product, at first the ____ product will be dominant due to the low _____.

Over time, ____ will be apparent because of the low ____.

A

Kinetic, activation energy

Thermodynamic, gibbs free energy

61
Q

Free Energy of Reaction

A

deltaGrxn = deltaGproducts - deltaGreactants

62
Q

Deriving standard free energy change from equilibrium constant

A

deltaGrxn = -RT ln Keq

T in kelvins

R is ideal gas constant

greater the value of Keq, the more postive the ln and the more negative the deltaG

63
Q

Determining Free Energy change for a reaction in Progress

A

deltaGrxn = deltaGrxn(standard) + RTlnQ = RTln(Q/Keq)

64
Q

If Q/Keq is less than 1, then free energy will be ______ and ______

If Q/Keq is more than 1, then free energy will be more _____ and _____. If this were the case, the reaction will move in the ____ direction until ______ is reached.

If Q/Keq is = 1, then free energy is ____ and ____ is met.

A

negative, spontaneous

positive, nonspontaneous

opposite , equilibrium

0, equilibrium

Chemistry (9 decks)

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