Thermochemistry

Question 1

what’s the diff between an isolated and closed system?

Answer 1

isolated cannot exchange E with outside

Closed can

Question 2

open system

Answer 2

can exchange E and matter with outside

Question 3

what do these mean:
isothermal
adiabatic
isobaric

Answer 3

isothermal is T remains const
adiabatic is no exchange of heat
isobaric is P remains constant

Question 4

what is calorimetry?

Answer 4

it measures heat changes

q = mcdeltaT

m = mass
c = specific heat
mc = heat capacity
q = heat absorbed or released

Question 5

what are state functions?

Answer 5

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)

Question 6

What is enthalpy, H and equations?

Answer 6

H expresses the heat change at constant P.

deltaHrxn = Hprod - Hreact
+ means endothermic
- is exo

Question 7

what is standard heat of formation?

Answer 7

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!

Question 8

What is standard heat of rxn?

Answer 8

deltaHrxn = sum of deltaHfprod-deltaHfreact

this happens under stp

Question 9

Hess’ Law about enthalpies?

Answer 9

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!

Question 10

how can you know delta H for reverse?

Answer 10

opposite of forward

Question 11

Bond dissoc E

Answer 11

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

Question 12

What is heats of combustion?

Answer 12

deltaHcomb

produces co2 and h20

Question 13

What is Entropy and equation?

Answer 13

deltaS = qrev/T

qrev is heat added to system undergoing reversible process.
T is absoluteT

Question 14

spontaneous process occurs so that S increases until…

Answer 14

Equilibrium

Question 15

Gibbs free E

Answer 15

change in free E, max E released by a process

Question 16

delta G
+
-
0

Answer 16

+ is not spont
- is spont
0 is eq deltaH = TdeltaS

Question 17

Eq for G, H T, S?

Answer 17

deltaG = deltaH-deltaS

Question 18

what is deltaGrxn at start? and after the rxn starts?

Answer 18

deltaGrxn = -RT ln Keq

deltaGrxn = deltaGstandard + RT ln Keq

Question 19

Think of delta G this way…

Answer 19

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

Question 20

heat of vap and heat of fusion

Answer 20

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

Question 21

what is work in relation to G?

Answer 21

Work = |deltaG|

Question 22

can an open system have infinite heat gain?

Answer 22

no, it will come to equilibrium with the environment

only a closed system can gain infinite heat