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Chem year 1 > 137A - thermodynamics > Flashcards

137A - thermodynamics Flashcards

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1
Q

what is isobaric

A

reaction at constant pressure

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2
Q

what is isochloric

A

reaction at constant volume

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3
Q

what is a state function + examples

A

just values (doesn’t matter how you got there) e.g. enthalpy, entropy, pressure

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4
Q

what is a path function

A

value when it matters how you got there e.g. health, work done

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5
Q

what is an extensive property

A

properties dependant on amount of “stuff” you have e.g. mass, internal E, heat capacity

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6
Q

what is an intensive property

A

properties not dependant on amount of “stuff”/ molar properties e.g. specific heat cap, molar enthalpy

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7
Q

how many degrees of freedom does every atom have

A

3

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8
Q

how many degrees of freedom does a molecule have

A

3N (N= number of atoms in molecule)

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9
Q

why do linear molecules only have 2 rotational degrees of freedom not 3

A

because rotating around z doesn’t make any difference

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10
Q

equation for working out vibrational degrees of freedom for linear molecule

A

x= 3N-5

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11
Q

equation for working out vibrational degrees of freedom for non-linear molecule

A

X=3N-6

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12
Q

What is an isolated system

A

no transfer of matter or energy

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13
Q

what is an open system

A

matter or energy can be removed or added

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14
Q

what is a closed system

A

cannot take matter but can transfer energy In heat or work

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15
Q

what is an adiabatic system

A

no transfer of energy by heat, but work can be done on system by surroundings+ visa versa

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16
Q

What are energy levels are rarely populated unless at very high temperatures

A

vibrational. At low temps only translational are occupied. As temp increases distribution increases over more levels

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17
Q

Describe the spacing in energy levels. Why are transitional levels well populated?

A

translational are very closely spaced, then rotational, then vibrational which are higher in energy. Relative population of levels depends on the energy gap between them

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18
Q

How much does each degree of freedom contribute to the molar internal E

A

RT/2

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19
Q

What is the internal E of a diatomic gas with 6 degrees of freedom

A

E= 3RT

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20
Q

Why do vibrational degrees of freedom not contribute to the internal E

A

only active degrees of freedom contribute; vibrational levels are largely spaced and rarely occupied

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21
Q

define the terms of the first law of thermodynamics

A

△U= internal energy
q= energy in heat
w= energy in work

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22
Q

What is the first law of thermodynamics

A

the internal energy of an isolated system is constant

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23
Q

How many degrees of freedom does N2 have and its molar internal E at 25°

A

3x2= 6
3 trans, 2 rot, 1 vibrational
3+2=5 x (RT/2) = 6190Jmol-1

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24
Q

How many degrees of freedom does O3 have and its molar internal E at 25°

A

3x3= 9 degrees freedom
3 trans, 3 rot, 3 vib
3+3=6 x (RT/2) = 7.4kJmol-1

25
Q

units of internal E

A

kJ/ J

26
Q

units of molar internal E

A

kJmol-1 or Jmol-1

27
Q

Why can’t you use equipartition theory to determine the internal energy of ethanol at room temperature

A

It’s a liquid at room temperature, equipartition theory tells us about ideal gases

28
Q

if the system is doing work on the surrounding the work done is positive/negative

A

negative/exothermic (energy transferred from system to surroundings)

29
Q

if the surroundings is doing work on the system the work done is positive/negative

A

positive/ endothermic (energy transferred from surroundings to system)

30
Q

if work done is negative, the internal E of the system rises/falls

A

falls

31
Q

if the reaction is exothermic does the internal E of the system rise/fall

A

fall

32
Q

if the reaction is endothermic does the internal E of the system rise/fall

A

rise

33
Q

what is isothermal expansion

A

temp remains constant when a gas expands

34
Q

label the terms (enthalpy change at constant pressure)

A

△H= enthalpy change
△U = change in internal E
p△v = work done

35
Q

How else can this equation be written as when containing the ideal gas law

A

△H = △U + △nRT

36
Q

what is the work done when something expands

A

work done by system on surroundings, which means work done is negative

37
Q

**what does this equation mean w = -w

A

w = -w
w= work done on system
-w= work done by system

38
Q

define the heat capacity of a material

A

amount of energy required to raise the temp of a material by 1K

39
Q

why are heat capacities at constant pressure bigger than heat capacities at constant volume (Cp = Cv + R)

A

because if we are at constant pressure the gas has to do work in expanding

40
Q

does heat capacity vary with temperature

A

yes

41
Q

how much does each transitional DOF contribute to the heat capacity

A

1/2 R

42
Q

how much does each vibrational DOF contribute to the heat capacity

A

R

43
Q

Define the terms (relation between enthalpies at 2 different temps) △H (T) = △H (T2) + Cp x(T-T2)

A

△H= enthalpy at first temp
△H (T2) = enthalpy at second temp
Cp = difference in heat capacity between products and reactants are constant pressure

44
Q

what temp are standard enthalpies of formation measured at

A

25°

45
Q

what phase change is △H vapourisation

A

liquid to gas

46
Q

what phase change is △H fusion

A

solid to liquid

47
Q

why does enthalpy of vapourisation> fusion

A

it takes more E to go from liquid to gas than solid to liquid (complete bond breaking)

48
Q

Heat capacity units

A

JK-1mol-1

49
Q

what is a bomb calorimeter

A

container where volume of the system cannot change but pressure can when the reaction happens

50
Q

when a bomb calorimeter is involved in a question with a heat capacity, is the heat capacity Cv or Cp

A

Cv (capacity at constant volume)

51
Q

what is the second law of thermodynamics (entropy)

A

the entropy of a system tends to increase

52
Q

what does this equation say

A

the entropy increase is greater at lower temperatures for a given amount of heat

53
Q

what does it mean if a reaction is spontaneous

A

will happen without needing work being done

54
Q

equation to work out total permutations in a system

A
55
Q

example of macrostate arrangement

A
56
Q

what is a microstate arrangement

A
57
Q

equation for the probability of any given microstate occurring

A

no. micro states (we care about)/ total no. permutations

58
Q

**label units in the equation: q= Cp x n x △T

A

q= energy in form of heat
Cp= heat capacity
n= moles
△T= change in temp

59
Q

Consider a system with two bulbs and 20 particles. How many micro states are there where all 20 particles are in one

A

2 microstates (all in bulb A or all in B)

Chem year 1 (26 decks)

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