chem 106 quiz 4 Flashcards
rule of thumb for temperature and reaction rate
rate constants double for every 10*C increase
reaction rate is affected by both ? and ?
concentration and temperature
overall, reaction rate is mostly controlled by
activation energy
rates increase ? with temperature
exponentially
rates depend on 3 things
- fraction of molecules with KE > Ea
- collisions/sec
- orientation (fraction of collisions with correct orientation)
Arrhenius Equation
k = A*e^(-Ea/RT)
Arrhenius Plot
lnk vs 1/T
slope = -Ea/R
y-intercept is lnA
to measure Ea experimentally,
find k at at least two temperatures
slope = -Ea/R on plot of lnk vs 1/T
elementary step
one, uninterrupted step
rate law is first order for each reactant
multi-step reactions
slow and fast step
intermediate
slow step is rate determining step
dynamic equilibrium
rate of forward reaction = rate of backward reaction
catalyst
speeds up a reaction by lowering the Ea, changes the mechanism, not consumed in the reaction
two kinds of catalysts
homogeneous (same state/phase as reaction) and heterogeneous (diff. phase)
catalysts (do/do not) affect overall thermodynamics
do not
enthalpy and equilibrium do not change
the equilibrium constant is equal to
k,f / k,r = [product] / [reactant]
for gases, Keq = Kp (use ? instead of ?)
pressure; concentration
pressure for k is always ?
concentration for k is always ?
atm
M
solid concentration doesn’t mean anything, so
exclude it from the calculation of k
the concentration of a pure substance (i.e., water) is not changing, so
exclude it from the calculation of k
a weak base is expected to have a (small/large) k because
small; won’t dissociate much
k will be small for (soluble/insoluble) reactants
insoluble (or not very soluble)
how to use ICE
initial
change
equilibrium
should be able to fill in the blanks
initial of products should be zero
use mole ratios (stoichiometric coefficients)
reaction quotient (Q) predicts
the direction of reaction
if Q = Keq
the reaction is at equilibrium
if Q < Keq
the reaction will shift to the right (to make more products, thus increasing Q)
if Q > Keq
the reaction will shift to the left (to make more reactants, thus decreasing Q)
always check ? when solving for equilibrium pressures
that the Keq values match up
if k=1 reaction favors
neither side
if k>1 reaction favors
products
if k<1 reaction favors
reactants
