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CHM1051 > Thermodynamics > Flashcards

Thermodynamics Flashcards

1
Q

law of conservation of energy

A

energy can be converted from one form to another but energy cannot be created or destroyed

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2
Q

thermodynamics

A

the study of the energy of a system

- can predict spontaneous reactions

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3
Q

AU

A

internal energy

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4
Q

AH

A

enthalpy

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5
Q

AS

A

entropy

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6
Q

AG

A

Gibbs free energy

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7
Q

AX are?

A

state functions and are usually a change in energy

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8
Q

state function

A

initial and final states of a system (ignores the journey)

delta = products - reactants

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9
Q

path functions

A
  • heat (q) and work (w) are the consequences of change
  • not predicable from AU (their sum)
  • depend on the way change occurs (path function)
  • the whole journey
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10
Q

system

A

might be chemical reaction and chemicals involved

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11
Q

boundary

A

separates the system and surroundings

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12
Q

universe

A

system and surroundings

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13
Q

temerpature

A

in kelvins - the transfer from hotter to cooler bodies

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14
Q

heat

A

the energy that transfers from hotter to cooler objects

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15
Q

work

A

motion against an opposing force

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16
Q

SI units for energy, work and heat

A

1J = 1Kgm^2s^-2

1J is the amount of KE possessed by a 2kg object moving at speed of one meter per second

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17
Q

open system

A

gain and lose mass or energy across boundaries eg. human body

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18
Q

closed systems

A

can absorb or release energy but not mass across a boundary.

  • mass is constant
  • light bulb
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19
Q

isolated systems

A

cannot exchange matter or energy with the surroundings

  • energy is constant (cannot be created or destroyed)
  • stoppered vacuum flask
  • adiabatic: no heat transfer to surroundings
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20
Q

adiabatic systems

A

heat or matter cannot enter or leave the system

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21
Q

internal energy

A

sum of nuclear, electronic, vibrational, rotational, translational and interactional energy of all the individual particles in a sample of matter

  • =0 in an isolated system - energy (heat, light, sound) can change
  • AU = q + w
  • AU = q - (P deltaV)
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22
Q

enthalpy

A

heat absorbed or evolved by a chemical system and may be determined y temp change or physical change under constant pressure

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23
Q

entropy

A

measure of the number of ways energy is distributed throughout a chemical system. value is related to enthalpy at a particular temperature

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24
Q

Gibbs equation

A

G = H - TS

enthalpy - temperature x entropy

25
Q

exothermic

A

releases energy

  • enthalpy of reactants is higher than enthalpy of products
  • delta H is less than 0
26
Q

endothermic

A

absorbs energy

  • reactants have lower enthalpy than products
  • delta H is positive
27
Q

enthalpy and its equations

A

measure of energy in a thermodynamic system

H = U + pV

enthalpy (J)
internal energy (J)
pressure (Pa)
volume (m3)

but we can’t measure enthalpy of a system so we measure the change

28
Q

measure of change in enthalpy equation

A

AH = q (subscript) p

q is positive with heat supplied (melt ice)
q is negative with heat given out (explosion)

29
Q

+w and -w

A

+w is work done on the system (energy enters) - work done by a wind turbine

-w is work done by the system (energy leaves) - work done by car engine

30
Q

standard enthalpy

A
  • standard values so reactions can be compared
  • pressure 10^5 Pa (gases)
  • concentration 1M (solutions)
  • 25 degrees or 298K usually (not one of the standard states though)
31
Q

standard enthalpy of formation

A

enthalpy change of formation of 1 mol of substance in its standard form from its constitutive elements in their standard states

32
Q

standard enthalpy of reaction

A

sum of the enthalpy of formation of the products - the sum of enthalpy of formation of reactants

33
Q

phase diagrams

A

describes the existence of various phases of matter (solid, liquid, gas) for a substance as a function of pressure and temperature

  • depends on bonding and intermolecular forces
  • accompanied by changes in heat (energy)
34
Q

equation of heat during heating of phase

A

q = mCAT

35
Q

equation of heat during phase transitions

A

q = mAH

constant pressure during changes

  • ice (more ordered) moves to a liquid which is less ordered (endothermic)
  • stream (less ordered) moves to liquid (more ordered) - exothermic
36
Q

why does H2O have a negative slope between solid and liquid?

A

ice is less dense than water

37
Q

what does a bomb calorimeter measure and its equations?

A
  • measures AU
  • constant V AU = q - P delta V so delta V = 0 so AU = q (subscript) v

q reaction = - Ccalorimeter AT

C is the calorimeter constant

38
Q

how does a bomb calorimeter work?

A

combustion causes water to heat. the heat gained by the calorimeter, q calorimeter, = the heat liberated by combustion

q calorimeter (J) = (C calorimeter J/k)(delta T sample k)

39
Q

bomb calorimeter in a closed system

A 
heat is constant 
q system + q surroundings = 0
q reaction (J) = - q calorimeter (J)
40
Q

system and surroundings of a bomb calorimeter

A

system: reaction in calorimeter
surroundings: calorimeter including water

41
Q

what does a coffee cup calorimeter measure? and equation

A

delta H at constant pressure (gas loss) so delta H = q (subscript) p

qp = mCAT

C is the heat for 1g to be heated by 1 degree (4.18J/k for water)

42
Q

Hess’ Law

A

makes use of state functions by sequential reactions

  • try to organise to make one thing from one equation equal something from another and can then determine enthalpy of that reaction
43
Q

what is spontaneity?

A

order to disorder

  • entropy goes from order to disorder (does not relate to exo or endo)
  • less moles to more moles (reactants to products)
  • increase in temp = more disporder
  • change is state: solid to liquid to gas is less orderly
  • solid dissolved in light
  • gas dissolved in liquid goes into the atmosphere
44
Q

spontaneity and entropy

A

AU universe = AU system + AU surroundings

AU sustem = - AU surroundings

45
Q

spontaneous change

A

reactions occur without a constant input of energy

- order to disorder; entropy increases

46
Q

non-spontaneous reaction

A

require work to be done

47
Q

facts about sponteneity

A

exo and endo tell us nothing. delta H is not a good predictor. has nothing to do with rate of the reaction

48
Q

entropy

A

the state of order of a system

49
Q

standard molar entropy

A

the entropy per mole of a pure substance while in its standard state (1atm gas, 1M solution, pure substance)

units are J/mol/k and values are usually tabulated at 298k

  • higher entropy = more disorder
  • higher entropy in ionic solids with weaker bonds
50
Q

equation for standard molar entropy of reaction

A

standard entropy of reaction = standard entropy of products - standard entropy of reactants

take mole ratios into account!!

51
Q

entropy of the surroundings compared to enthalpy of system

A

AS surroundings = -AH system/T

If exo, heat from system to surroundings and AH system is negative
heat creates more disorder so AS surroundings is positive
keep units for AS and AH consistent

52
Q

Gibbs energy and spontaneity

A

standard entropy, enthalpy and Gibbs can be used to determine spontaneity at standard conditions. standard enthalpy of formation of Gibbs and enthalpy are zero at standard states at all temperatures.

standard delta G = standard delta H - T x delta standard S

standard delta G < 0 for spontaneous
G = 0 for equilibrium
G > 0 for non-spontaneous

53
Q

second law of thermodynamics

A

for a spontaneous process the total energy of the universe increases (AS total > 0)

AS universe = AS system + AS surroundings > 0

if AS is negative, the reaction is non-spontaneous

AS = 0 is equilibrium

AS system = -AS surroundings

54
Q

Boltzmann’s formula

A

S = k x ln x w

55
Q

third law of thermodynamics

A

a point at which a perfect crystal can form
enthalpy = 0
k = 0

56
Q

equilibrium constant

A

k = concentrations of products over concentration of reactants

57
Q

when not at equilibrium, k becomes?

A

Q
if only A and B are present initially, Q = 0
Q< k reaction is forwards
Q > k reaction is reversed

58
Q

standard Gibbs free energy and Gibbs free energy

A

delta G reaction = delta standard G reaction + RTlnQ

standard delta G reaction is for standard conditions
this is a correction for non-standard conditions
Gibbs free energy decreases to a minimum equilibrium and then back up (AGr = 0 when K = Q)

59
Q

the reaction isotherm

A

k = e ^ (-AGr/RT)

if AGr = 0, k = 1
G > 0, k < 1 and reactants predominate
G < 0, k > 1 and products predominate

CHM1051 (9 decks)

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