Module 2 Flashcards
(27 cards)
What is Gibbs free energy?
Gibbs free energy (G) is a thermodynamic quantity that tells us whether a chemical reaction or process will occur spontaneously at constant temperature and pressure.
G = H -TS
When does a reaction occur spontaneously? When does it not?
G < 0, spontaneous
G > 0, non-spontaneous (requires energy input)
G = 0, equilibrium (no net change over time)
At the midpoint of a titration [HA] = …
[HA] = [A-], so pH = pKa
what’s the difference between pKa and pH?
pKa indicates whether an acid is a strong acid or a weak acid.
high pKa = weak acid
low pKa = strong acid
pH indicates whether a system is acidic or alkaline.
high pH = alkaline
low pH = acidic
If the pKa of an acid is high, it is a weak acid, and if the pKa of an acid is low, it is a strong acid.
If the pH of a system is high, the system is alkaline, but if the pH is low, that system is acidic.
Put these from strongest to weakest interactions
hydrogen bonding, ion-dipole, ion-ion, London dispersion, dipole dipole, covalent.
strongest
ion-ion; charged + charged
covalent
ion-dipole; charged + partially charged
hydrogen; type of dipole-dipole, H + electronegative atoms
dipole-dipole; dipole + dipole in polar molecules
London dispersion; temporary dipole + temporary dipole, nonpolar substances
weakest
Why is a covalent bond more stable than a non-covalent bond
covalent bonds require more energy to break, meaning its more stable.
Which atom is the donor and which is the receiver in a hydrogen bond
Atom that the H is from = donor
atom w non bonded electron = acceptor
According to Coulomb’s law, the smaller the distance…
the smaller the distance, the bigger the force (inverse square law)
What is relative permittivity and how does it relate to the screening effect?
the relative permittivity (epsilon, dielectric constant) accounts for force not in vacuum
the screening effect says that the higher epsilon, te lower the force.
E = keq1q2/er (where E is energy and e is epsilon)
give examples of non polar and hydrophobic compounds
benzene and hexane
*C-H => non polar
what is the hydrophobic effect?
The hydrophobic effect is the tendency of nonpolar molecules to clump together in water, while being excluded by water. This effect is a result of the difference in density between water and nonpolar molecules.
what does polarizable mean
can take an induced dipole
give the distance of these:
charge-dipole
dipole induced dipole
charge induced dipole
charge-charge
dipole-dipole
van der waals
charge-charge: 1/r
charge-dipole: 1/r^2
dipole-dipole: 1/r^3
charge induced dipole: 1/r^4
dipole induced dipole: 1/r^5
van der waals: 1/r^6
is an acid a proton donor or acceptor? what about a base?
acid: proton donor
base: proton acceptor
explain what the size of the equilibrium constant means
K > 1, equ favours products
K < 1 , equ favours reactants
Makes sense since
K = [P]/[R]
what is kw and why is it useful
“Kw” stands for the “ionic product of water,” which is a constant value representing the equilibrium constant for the self-ionization of water.
A higher Kw value indicates a greater degree of water dissociation into ions.
It shows the balance between hydronium and hydroxide ions in water.
at room temp, 1 x 10^-14 moml^2 dm^-6 (also at neutral solution, [HA-] = [A-])
what is pKw equal to
pKw = pH + pOH = 14
pH = log(1/H+) = -log(H+)
pH = 3 is ____ more acidic than pH = 4
10 times more
pKa + pKb = …
pKa + pKb = 14
pKa = -log___
pKa = -logka
how does acidity affect the willingness to lose/give protons?
the more acidic, the more it is willing to give a proton. *acids are DONORS
the more acidic a substance is the ___ the ka and the ___ the pKa
the more acidic a substance is the higher the ka and the lower the pKa.
Makes sense:
Ka = [A-][H+]/[HA]
if Ka is big then [A-][H+] is big => more disassociation => more protons given => stronger acid
give the henderson hasselbalch equation
pH = pKa + log [A-]/[HA]
in a titration, the ___ of a titrant is known and the ___ of the analyte is known
the concentration of a titrant is known and the volume of the analyte is known
Goal of titration: finding the conc or Kequ of the analyte (whats in the beaker)
