Exam 2 Flashcards
Standard state
a reference point used to calculate a substance’s properties under different conditions
1 M
1 atm
example of a compound in its standard state
CO2 is a gas in the standard state
Why do reactions proceed to a lower energy state when they reach equilibrium? (mathematically)
G = -RTln(K)
K=1 at equilibrium, so G will equal 0
Why do reactions proceed to a lower energy state when they reach equilibrium? (conceptually)
as a reaction approaches equilibrium Q=K
when Q=K, ln(Q/K)=0 and therefore G=0
*this is still very mathematical
G when Q
reaction has more reactants, needs to shift right towards the products, so G is negative
G when Q>K
reaction has more products, needs to shift left towards the reactants, so G is positive
G when Q=K
system is equilibrium, so G is 0
G when K>1
G is negative
equilibrium is a state where there are more products than reactants, so the reaction proceeds right
Graph when K>1
equilibrium is closer to products
Graph when K<1
equilibrium is closer to reactants
G when K<1
G is positive
equilibrium is a state where there are more reactants than products, so the reaction proceeds left
difference between ΔG° and ΔG
ΔG° is always the same for a reaction since it is standard conditions and only changes with K. K is a set number at equilibrium.
ΔG differs for a reaction since it is related to ln(Q/K) and Q changes. ΔG is the only one that changes as a reaction proceeds and Q changes.
axial hydrogens are _____ to one another
anti
equatorial hydrogens are _____ to one another
gauche
gauche
60 degrees
after a ring flip, what position does an equatorial constituent have?
axial
after a ring flip, what position does a pointing down consitutent have?
pointing down
which way do constituents “move” positions when going from right to left in ring flip?
clockwise
which way do consitiuents “move” positions when going from left to right in ring flip?
counter-clockwise
steric strain
the van der Waals repulsion between a substituent and nearby hydrogens
why is the equatorial position favored in cyclohexanes?
to minimize the steric strain
why is the equatorial position more favored when the size of the constituents increases?
as the steric bulk of the constituents increases, the steric strain also increases, so want to minimize this
relationship between ΔG and A-value
ΔG can be called an A-value when talking about the equatorial vs. axial position
makes sense that as K increases and there are more axial conformations, ΔG becomes more negative and more stable, which means that A-value points to more axial products
^all adds up
A-values
indicate how much the equatorial position is favored over the axial position
Relationship between ΔG and stability
the more negative ΔG is the more stable it is because it has lower free energy
Bronsted-Lowry acid
a substance that can donate a proton (H+)
Bronsted-Lowry base
a substance that can accept a proton
amphoteric
water’s ability to act as an acid or a base
autoionization of water
ionize H2O to give off H+ and OH- ions
equilibrium constant of the autoionization of water (Kw)
1.0 * 10-14
Kw = [H3O+] [OH-]
*when H3O+ > OH- solution is acidic, and vice-versa
Lewis acid
a compound that accepts an electron pair
Lewis base
a compound that donates an electron pair
Arrhenius acid
specifically dissociates into H+ ions in water
Arrhenius base
specifically dissociates into OH- ions in water
What do curved arrows represent?
collisions of molecules that lead to chemical reactions
Where do curved arrows always start?
the Lewis base (electron source)
Why are Lewis bases known as nucleophiles?
their negatively charged lone pairs are attracted to the positive nucleus of other atoms
Why are Lewis acids known as electrophiles?
their partially positive atoms are attracted to electrons
Carbocation
carbon with a formal + charge
often a Lewis acid since positive charge is attracted to electrons
Acetic acid formula
CH3COOH
*weak acid
What do we mean by stable?
lower in free energy
What does the “p” indicate in like pH?
indicates the -log of whatever follows it
for example, pOH = -log (OH)
strong electrolyte
a combined name for strong bases and acids
there is no equilibrium here. reaction goes to completion
inductive affect
ability for electronegative atoms to removed electron density from the other negatively charged constituents through SIGMA bonds
can make a conjugate base more stable
why do stronger acids have a higher K?
they have more stable conjugate bases (weaker) so the reaction wants to go towards the products
in addition, more stable conjugate bases means that enthalpy goes down, so G is most likely negative as well and the reaction will proceed right
what does a lower pKa indicate?
a stronger acid
there is a greater concentration of H+ ions
when is it appropriate to make the size argument when looking at conjugate bases?
if comparing two elements that are actually carrying the negative charge
ex: O- vs. S-
polarizability
the ability to form instant dipoles
relationship between polarizability and size
larger molecules are generally more polarizable than smaller molecules
when can you not use the polarizability argument even when looking at elements carrying the negative charge?
if the elements are in the same row of the periodic table
there is not a big enough size difference
need to be in different rows with different orbitals
what should you look at when you are examining the elements carrying the negative charge but they are in the same row?
electronegativity
do strong acids have a Ka or pKa?
no
there is no equilibrium, so they have no Ka
where does the inductive effect occur?
sigma bonds with two electronegative species sharing electron density
where does resonance occur?
pi-bonds
move electrons through the double bonds
