Thermochemistry Flashcards
what’s the diff between an isolated and closed system?
isolated cannot exchange E with outside
Closed can
open system
can exchange E and matter with outside
what do these mean:
isothermal
adiabatic
isobaric
isothermal is T remains const
adiabatic is no exchange of heat
isobaric is P remains constant
what is calorimetry?
it measures heat changes
q = mcdeltaT
m = mass c = specific heat mc = heat capacity q = heat absorbed or released
what are state functions?
properties that only depend on initial and final states of systme, independent of path
Eg: P, V, T, H(enthalpy), S(entropy), G(free Gibbs), E(energy)
What is enthalpy, H and equations?
H expresses the heat change at constant P.
deltaHrxn = Hprod - Hreact
+ means endothermic
- is exo
what is standard heat of formation?
deltaHf
the enthalpy change that would occur if one mole of a compound was formed directly from its elements in their standard state.
NB the enthalpy change of element in ss is 0!
What is standard heat of rxn?
deltaHrxn = sum of deltaHfprod-deltaHfreact
this happens under stp
Hess’ Law about enthalpies?
they are additive
Br2 (l) –> 2 Br deltaH1
2Br –> Br2 (g) deltaH2
Br2 (l) –> Br2 (g) H1+H2
PS. this would be heat of vaporization!
how can you know delta H for reverse?
opposite of forward
Bond dissoc E
avg E req to break bond in 1 mole gas
Bond breaking is always exo! it takes E to pull them apart, no matter what
Bond formation is always endo
What is heats of combustion?
deltaHcomb
produces co2 and h20
What is Entropy and equation?
deltaS = qrev/T
qrev is heat added to system undergoing reversible process.
T is absoluteT
spontaneous process occurs so that S increases until…
Equilibrium
Gibbs free E
change in free E, max E released by a process
delta G
+
-
0
+ is not spont
- is spont
0 is eq deltaH = TdeltaS
Eq for G, H T, S?
deltaG = deltaH-deltaS
what is deltaGrxn at start? and after the rxn starts?
deltaGrxn = -RT ln Keq
deltaGrxn = deltaGstandard + RT ln Keq
Think of delta G this way…
H2o (l) + heat –> H2o (g) boiling
G = H-TS
l–>g so S is +
endothermic so H +
G will be - and spont if TS>H, and it will be if T>100C, boiling point! Otherwise, it won’t happen, exo
heat of vap and heat of fusion
vap is from l to g
fusion is s to l
keep in mind this is the phase change only, like 0C ice-0C water is fusion
what is work in relation to G?
Work = |deltaG|
can an open system have infinite heat gain?
no, it will come to equilibrium with the environment
only a closed system can gain infinite heat
