chap 12 Flashcards
(26 cards)
first law of thermodynamics
Euni = Esys + Esurr
define enthalpy(H)
thermal enegry at constant pressure qp (kJ/mol)
define exothermic. + or -
transfer of thermal energy from system to surroundings. so system gets colder and surroundings warmer
-qsys=+qsurr
-
define endothermic. + or -
transfers of thermal energy from surroundings to system. so system gets warmer and surroundings colder.
+qsys=-qsurr
+
define state function
independent of the path taken btwn equilibrium states
what is Gibbs function formula?
🔺️G=🔺️H - T🔺️S
where 🔺️G is Gibbs function “free energy” or amount of energy avaliable to do useful work (kJ/mol)
🔺️H = enthalpy qp (kJ/mol)
T = absolute temp (K)
🔺️S = entropy- energy dispersal randomness J/kJ(remember to convert to kJ)energy NOT avaliable to do useful work
define spontaneous process
a process that occurs without continuous outside intervention.(ex:water and dye, airbags, fire, rust)
if spontaneous reverse is nonspontaneous. not always exothermic
define nonspontaneous process
process that only occurs as long as energy is continually added to system(ex: photosynthesis)
the second law of thermodynamics
🔺️Suni=🔺️Ssurr + 🔺️Ssys>0
entropy(disorder) (S) how energy is dispersed in a thermodynamic system.
determining spontaneity
burning wood: 🔺️H enthalpy exo(-) or endo(+)? exo(-)
🔺️S entropy incre(+) or decre(-)? incree(+)
is it spon? 🔺️G=(-) - (+) so 🔺️G=(-) so spontaneous
define accessible microstate
a unique arrangement of the positions and momentums of the particles in a thermodynamic system
what is entropy affected by?
mass, molecular structure, mass distribution, and rigidity. bigger the higher entropy
define entropy (S)
any deviation from the perfect arrangement (absolute zero) you will increase in entropy and gain microstates
define standard molar entropy(S°) °- standard working conditions
the absolute entropy of one mole of a substance in its standard state at a 1 bar(1 atm) and 25°C (298K) always positive based on these conditions some ions in (aq) they’ll be negative standard molar entropy
_____ polarizability = ______ microstates
more, more
______ size/complexity = ______ entropy
larger , larger
entropy(S) _______ with temperature(T)
increases
entropy ____ when volume ___
increases, increases
entropy _______ when the number of independent moles ____
increase, increase
formation of rust:
4Fe(s) + 3O2(g) –> 2Fe2O3(s)
Hrxn = −1648.4 kJ/mol
S°sys = –549.4 J/mol*K
G kJ/mol = -1648.4 kJ/mol - (298K)(-0.5494 kJ/mol x K) = -1484.7 kJ/mol
______ 273K =sponatneous
______ 273K = non spontaneous
above, below
formation of rust: solve for T at equillbrium:
4Fe(s) + 3O2(g) –> 2Fe2O3(s)
Hrxn = −1648.4 kJ/mol
S°sys = –549.4 J/mol*K
G = 0 = - 1648.4 kJ/mol - T(-0.5494 kJ/mol K) T= 3000
beyond this would be nonspon
G°sys S°uni
<0 >0 __________
>0 <0 __________
0 0. __________
spontaneous
nonspontaneous
no change, equillibrium
H S G
- + always <0 ________
- - <0 @ lower temp ____
+ + <0 @ higher temp ___
+ - always >0 ________
always spon
spon at lower temp
spon at higher temp
never spon
