3d Flashcards
what conditions are needed the measure the temp dependence of U
we need V to be constant,, so W is 0,,
so dU = dQ
aka change in internal energy = change in heat exchange
bc U = q+w
and if w = 0 bc volume is constant,, (expansion = increase in volume) constant vol = no work bc no expansion so U = Q
Cv,m aka molar heat capacity at constant volume =
(dQ/dT)V
when N = 1
when we have state A and state B,, how can we find the heat difference between the 2.
we do Qb - Qa
where Qb is the heat of state b and Qa is the heat of state A.
=
Ub - Ua+ p(Vb - Va)
= (Ub+ pVb) - (Ua+ pVa)
what is enthalpy
H
sum of internal energy + pV
equation for enthalpy // what it is // the equation for the definition
H = U + pV
change in enthalpy in terms of q
Hb - Ha = qb - qa
if we have 3 diff reaction that link,, how can we find delta H if we are given delta for all 3 reactions
delta H3 = delta H2 + delta H1
hess law
enthalpy is independent of route taken to get there,, there can be many different steps but they all end up giving the same total enthalpy
temp standard state
298.15k
pressure standard state in bar and pa
1 bar
100,000 pa
moles in standard state
1 mol kg-1
enthalpy of formation equation weird way
(- rea - rea ) + pro + pro
aka pro - reactants
Cpm equation involving enthalpy, temp and pressure
(dH/dT)p
what is enthalpy a function of. aka enthalpy is enthalpy bc of what (when t isnt standard value)
a function of temperature
relation of H and T (when t isnt standard temp)
H(T P N) - H ( To P N)
u just put the values in for the diff compounds
what effects H and what is thr equation that links them all
H is affected by U and pV
so delta H = deltaU + delta(PV)in
in an ideal gas,,, U and PV are function of what
temperature
to make pressure a factor that effects a gas,, what must happen
there must be intermolecular forces of attraction,, these are not present in an ideal gas
so we think of van der waals interactions
do solids and liquids have a large or small volume change
solids and liquids have a small volume change
why do solids and liquids have a small volume chnage
bc they have a low compressability
delta H for liquids and solids,, due to pressure being an effect bc they have van der waals and low compressability
delta H = V deltaP
not exactly tho. its an approx
the progress of a reaction can be written as what
a single parameter:
E but curly ish
if we have A + B –> 2C ,, write how we find thr change in molar quantities of the reaction
we do
dNa/-1 = dNb/-1 = dNc/-2
which gives dE
aka the small change of extent of rea
equation for reaction velocity
dE / dT
Nk =
NAo - E
aka the moles of smt = initial moles - extent of reaction.
makes sense tbhh,, u look at how many moles u had to begin with and then u take away the extent of the reaction to see how much u have currently.
how do we find Na
NAo - E
how do we find Nb
NB = NBo - E
how do we find Nc. if c is the product and its stoich is 2
Nc = NCo + 2E
extent of a reaction and finding number of moles: if its a reactant with a stoichiometry of 1,, whatdo we do to fing it
moles = initial moles - 1E
bc its got a stoich of 1 and as the reaction takes place,, reactants decrease.
so we subtract the extent of reaction
finding extent of a reaction: how do we find current moles of a product with a stoichiometry of 3
current moles = initial moles + 3E
3 bc it has a stoichiometry of 3
and u add the extent of a reaction bc its a product,, and as the reaction occurs,, ur getting more product,, do u add extent of reaction!!!
U in terms of everything that affects it including E
U = U ( T V E)
if we have many diff chem reactions,, what else will we have many diff things of
we wll have many diff extents of reaction
one for each reaction im guessing
for us to add // subtract to the value of intiial moles to find the current moles
what does (dU / dE) VT mean
its the amount of heat evolved per unit change in the extent of reaction.
aka how heat change chnages with a ddiff extent of reaction.
bc this is in the dQ reaction
if dQ = …. (dU / dE) VT is negative,, what does this mean
it means that the reaction is exothermic
bc this is how the heat evolved changes as the ectent of reaction changes
so - heat = loss of heat = exothermic
and if its positive that means as the reaction goes on,, the heat evolved is positive so its endothermic as it would need to get heat from somewhere ,, aka the surroundings
how do we express H in terms of extent of reaction
H = H ( T p E)
heat of reaction per unit time change of E is the derivative of H wrt E =
H PT = (dH / dE ) pT
2nd law of thermodynamics
entropy of an isolated system will always increase over time
what is the change in internal energy if we return back to the original state,, and the system is closed
0 change in internal energy
there is no change
what is the equation that represents that change in internal energy for a closed system when there is a cycle,, is 0
theta (long curvy line) dU = 0
if we have a box type structure on a graph,, with p beig on the y axis and V being on the X axis,, and the corners being A B C and D going clockwise. A–> B will be the same,, but opposite to
C –> D
what is needed to get from A–> B is opposite of that needed to get from C–D bc its a carnot cycle.
in the box example we’re taling about a carnot cycle, to get from A –> B it absorbs heat so to get from C –> D it must
return the heat // get rid of it
do the opposite of what it did.
the work to get from AB issss=
Wab = N R theta1 ln ( Vb/Va)
theta 1 being the heat absorbed to get from A to B
if A to B was isothermal ,, no change in temp,, Wab would beeee
Wab = Q ab
Wcd would be
- Qcd
bc ur removing heat bc ur going to the lhs of the x axis,, which is a lower volume.
WBC is what compared to WDA
WBC = - WDA
what the total work done by the carnot cycle calculated using
all the different work. work done by each edge of the box to get to the different edges.
overall process eddiciency =
fancy n
overall process efficiency equation =
W / Qab
overall process efficience cannot exceed what
1
bc u cannot convert more than 100%
u do 1 - x to see how much was acc converted going between the diff states // corners
overall process efficacy equation in terms of 1 and the route taken to get to the different corners
u have 1 - ( theta 2 / theta 1)
efficacy of smt is dependent on what
theta 1 and theta 2
aka heat absorbed and returned in order to get to the diff states // corners of the box.
(Q1/T1) < (Q2/T2) means its what
it means its an irreversible processss!!!
what must occur for the process to be deemed as reversible
Q1/T1 = Q2 / T2
they must equal eachother to be reversible
what changes in reversible reactions and by how much
temp, pressure, vol can change
by ‘d’ infinetesly small amounts
irreversible reactions: t1 and q1 vs q2 and t2,, what is bigger than what
Q1/T1< Q2/T2
bc T1 is larger than T2.
the values arent equivalent meaning the values dont change by an infinitesily small amount like in a reversible reaction!!!!
so it must be an irreversible reaction.
in a carnot cycle,, the reversible cycle (infinitesity small changes) issss
the outside of the 2 boxes stuck together by an edge!! aka lowkey the circumference of it
in a carnot cycle,, when 2 cycles are combined,, where the 2 cucles combine,, what happens
these are the 2 adiabatic processes and they cancel out due to sign inversion
how do we offset the isotherm process in carnot cycles
we combine two of them
this offsets the isotherm processes by a infinitesimal temperature amount.
so that heat absorbed from A to A’ at T1 is Q1
and heat absorbed a;onh A’ to B at T1 + deltaT is Q’1
any process that has a closed path and chnages with infinitesimal small changes: we use the equation:
curly theta dQ/T = 0
which is the gibbs formula
bc DQ/T is a variable state
which gives us a measure of reversibility :
variable state = variables that describe the state of a dynamical system : yhh okay so shows reversibility bc we can see the state of the reaction!!
variable. smt that doesnt have a fixed pattern // changes.
