lecture 7 Flashcards
S universe equals what
S system + S surroundings
S universe can also be written in terms of gibbs:
S universe = - G // T
what’s gibbs at equilibrium or for reversible change
- or lower than 0
using equation G = H -TS,, how do we find the diff parts
H = pro - rea ( x stoichiometry)
S = pro - rea ( x stoichiometry)
make sure the units are the same
if S pro - S rea is positive,, what does this mean
the system entropy favours products
if H pro - H rea gives a positive number,; what does this mean
the reaction is endothermic
entropy is taken from the surroundings
for a gas,, what happens as pressure increases
as pressure increases,, entropy decreases
it becomes more negative
what is needed for a reaction to be spontaneous
Gibbs must be negative
Gibbs energy change for ideal monatomic gas
G = (5/2) nRT - TS
in gibbs equation G = H - TS,, what increases with temperature (when pressure is constant)
S and H both increase with temperature
equation that shows how small changes in Pressure and Temp induce changes in G
dG = V dp- S dT
if T is constant,, does pressure affect H
nope :)
S is always positive,, so a decrease in temp does what to G
decrease in temp = decrease in G
decrease is larger for systems with higher entropy
- S = dG/dT ) p
if V is always positive,,, increase in pressure does what to G
increase in pressure increases G
this increase is larger for systems with larger volumes
V = dG/dP ) T
grams of smt when u know it’s mr
X gmol-1
where X is the mr
when u have mass in gmol-1
what density units should u have
gm3
x1000 to get from dm to m
change in G for ice when
T = 273k
density = 917gdm-3
Pressure increases from 1 bar to 2 bars
use dG = Vdp - SdT
but T is constant so
dG/ dP ) T === V
find V (mass / density) and multiply this by pressure to get G
gibbs when temp is constant
dG / dP )T = V
using dG = Vdp- SdT
Gibbs when pressure is constant
dG = Vdp - SdT
dG/dT )p = -S
gibbs of a gas when given temp, pressure change
G = nRT ln(p1/po)
what is universal entropy
-G/T
when is 🔺H independent of temperature
when specific heat capacity of products and reactants are equal
how does gibbs change with increasing pressure
it increases
what does gibbs energy do in terms of entropy
reframed entropy changes in terms of energy
what must occur for reactions to occur spontaneously
gibbs must be negative,, it must be less than 0
what does integrated gibbs helmholtz equation describe gibbs
describes how gibbs energy changes with temperature
