Semester 2 Exam 2 Flashcards
Explain collision model
molecules must collide in order to react
molecules must be oriented in a certain way during collisions in order for a reaction to occur
many collisions do not lead to a reaction
orientation during collision determines whether atoms are in right position to form new bonds
conditions that affect reaction rate
concentration: more molecules -> more collisions
temp: molecule speed up means more collisions
the more collisions the faster the rxn
if molecules move too ___ they may bounce off of one another without change. why?
slow. Because the energy of the collision needs to overcome the bond energy
___ suggested molecules must have a certain ___ in order to react
Arrhenius, minimum amount of energyA
activation energy?
Ea: minimum energy required to start a rxn
Understand how to read a rxn energy diagram
A catalyst is used to ____ a reaction ____ being consumed
____ activation energy
speed up, without
lowers
look at a graph
Equilibrium is an exact ____ of 2 processes, which are ____ of one another
balance, opposite
chemical equilibrium:
occurs when opposing reactions are proceeding at an equal rate. Concentration of products and reactants remains constant.
rate of product formation = rate of reactant formation
Dynamic state
when the forward and reverse reactions are going on, but at the same speed. There is not a net change in system.
rates are equal, not concentrations
as concentration of reactants decreases the reaction slows, but reverse reaction increases in concentration and speeds up until system comes to equilibrium
basically 2 reactions coming to equilibrium and that state won’t change unless acted upon
dynamic state vs. chemical equilibrium?
Dynamic state refers to a system where processes are occurring continuously, but there is no net change. So, in this state, reactions (like a forward and reverse reaction) are still happening, but they balance each other out, and nothing is added or removed from the system. This doesn’t necessarily mean the system is at chemical equilibrium—it simply means reactions are still happening.
Chemical equilibrium is a special type of dynamic state. It occurs when the forward and reverse reactions happen at the same rate, so the concentrations of reactants and products remain constant over time. Although the reactions continue, there’s no net change in the system.
So yes, once a system is in a dynamic state, it can eventually reach chemical equilibrium if the conditions allow for it, where concentrations of reactants and products become constant.
Equilibrium constant
for
aA+bB-><-cC+dD
Kc =
[C]^c[D]^d
_____________
[A]^a[B]^b
significance of K
if K>1,
K<1,
K = 1
k has units of:
you can interpret it
equilibrium point for rxn lies far to right meaning high concentrations of product
opposite, high concentrations of reactant
neither is favored
no units
If you reverse an equation, you ___ K
invert
if you multiply coefficients in the equation by a constant, ___ K, to that same factor
raise
if you add 2 or more individual rxns to obtain an overall reaction, you ___ the Ks together
multiply
Le Chatelier’s Principle
if a system at equilibrium is disturbed by a change in temp, pressure, or concentration of components in rxn, the system will shift its equilibrium position to counteract the disturbance
3 ways an equilibrium can change
temp
pressure
adding/removing reactants or products
If a substance is added to a rxn the equilibrium will shift to ____ part of added subtance to reestabalish equilibrium
if a subtance is removed, the equilibrium wll shift to ___ that substance
consume
produce more of
Example in notes
IF a system at equilibrium has its volume decreased, its pressure will ____
the system will respond by shifting it’s equilibrium position to ____ the pressure (LC’s princip)
A system can reduce its pressure by ____ # of gas molecules so the equilibrium will move in direction of ____
opposite can happen as well!
increase
reduce
reducing
less gas molecules
example in notes
when temp is increased it is as if it were added as a ____ or ___ to the system at equilibrium.
Predict shift toward reactants or products if temp is raised for endo/exothermic reactions. If lowered?
reactant or product
Endo: product
Exo: reactants
endo: reactants
exo: products
Equilibrium position:
set of equilibrium concentrations
equilibrium ___ depends on initial concentrations, equilibrium ___ does not
position, constant
There is only ___ K for a system at a given temp, but there are an ___ # of EQ positions
one, infinite
what is Kp?
basically the same as Kc but calculated in terms of partial pressures of gasses.
relationship between Kp and Kc?
Kp = Kc[(RT)^Δn]
R = 0.08206 Latm/molk
K is ___ dependent
temperature
in calculation of K, ___ and ___ are not considered
pure liquids and solids
homo/heterogenous EQs
homo: all reactants and products are in same state in EQ
hetero: reactants and products are in >1 state
what is rxn quotient (Q)?
how to use it?
tells us which way the reaction is headed. Calculated just like K with subscripts c or p depending on the equation. The only difference is Q is not at equilibrium.
when Q<k, rxn goes to right
when Q>k, rxn goes to left
if Q=k, rxn is at EQ
Practice ICE table when calculating K
in notes
practice using ICE table to calculate EQ concentrations
in notes
solubility
amount of substance that dissolves in a given quantity of solvent at a given temp
units: mol/L (usually)
solubility is ___ Dependent
temperature
what is Ksp?
how to calculate when
AaBvb -><- aA + bB
solubility product of ionic solid. Shows how soluble an ionic solid is.
Ksp = [A]^a[B]^b
Learn to use ice tables w/ calculating Ksp and solubility!
in notes
If you want to compare Ksp of dissolution of ionic solids, ___ must be same
stoichiometry
Problem #49 ch.16
when determining direction of shift, solve for ___ and compare that to ____. JC WANTS YOU TO DO THIS ON EVERY PROBLEM YOU CALCULATE DIRECTION OF SHIFT
Q, K
5% rule & ice tables
if quantity x is > 5% of the initial value, it is better to use a quadratic equation. If not, we can assume x is negligible compared to the initial value. It’s usually doable when k = super small.
when doing 5% rule, always:
how?
check validity of assumptions in work!
calculate % difference
change/initial * 100
use this formula to compare answer when x is considered, and when x is assumed to be negligible
PRACTICE THIS!!!!
Common ion effect:
what must you do on tests?
solubility of an ionic compound is lower in a solution containing a common ion than in pure water. EQ shifts back left towards salt formation.
calculate solubility in both common ion solution and in pure water, then compare.
solubility rules:
- Most Nitrate (NO3-) salts are soluble
- Most salts with alkali metal ions (Li+, Na+) and ammonium ions (NH4+) are soluble
- Most Chloride, bromide, and iodide salts are soluble. Exceptions are salts with Ag+, Pb+, and Hg2+.
- Most sulfate (SO32-) salts are soluble except for those with Ba, Pb, Hg, and Ca
- Most hydroxides are slightly soluble except for NaOH and KOH
- Most Sulfide (S2-), carbonate (CO32-), chromate (CrO42-) and Phosphate (PO43-) salts are slightly soluble, except for those with conditions in rule 2
Effect of pH on solubility
solubility of an ionic compound with a strongly basic or medium anion increases w/ increased acidity.
similar to the common ion effect
basic anions that have higher solubility in acidic solutions:
OH-
S2-
CO32-
C2O42-
CrO4-
strong acids:
HCl, HNO3, H2SO4, HClO4, HBr, HI
pH in respect to [H+]
[H+] in respect to pH
pH = -log[H+]
[H+] = 10-pH
