Chemistry 132 Midterm

kinetics
refers to the rate at which a chemical reaction occurs (reaction rate)
reaction rate
the change in concentration of a reactant of product over time
rate law
the math expression relating the reaction rate to the rate constant and the reaction constant
reaction orders
x & y
are partial reactions that state the control on the rate of the reaction by each of the reactants individually
the overall reaction =
the sum of all the powers of all the partial reactions
reasons for different reactions
0^0 = a catalyst, thus independent of [reactant]
1^0 = increase collision rate which is dependent of [reactant]
2^0 = a) increase in collision rate
b) more effective collisions
c) a lower activation energy
d) often exothermic so an even lower activation energy
isolation method
how to determine the rate law by measuring the dependency of the reaction rate to the concentration of each reactant
Savante Arrhenius described
quantitatively the collision theory
Arrhenius Equation #1
k = Ae^(-Ea/RT)
Arrhenius Equation #2
derived by taking the natural log of equation #1
ln (k) = ln (A-Ea/RT)
Arrhenius Equation #3
determining Ea from two different T’s and k’s
ln (k1) = ln (A-Ea/RT1)
ln (k2) = ln (A-Ea/RT2)
ln (k1-k2) = Ea/R (ln( A-1/T1) – (ln(A – 1/T2))
Subtract these two and eliminate A
ln (k2/k1) = -Ea/R ((1/T2 – 1/T1))
About reversible reactions (4)
1) may occur slowly or rapidly
2) only products are formed
3) reactant disappear to the point of LR
4) con use stoichiometry of balanced chemical equation to find the moles of the product
About equilibrium reactions (5)
1) may occur slowly or rapidly
2) both products and reactants produced
3) stoichiometry not useful in finding moles
4) Equilibrium (keq)
5) ratio of reactants to products is useful in finding moles
Equilibrium
dynamic state where two processes are occurring at the same time in a system until no farther net change occurs
how to find moles in aequilibrium reaction
though stoichiometry is not useful, there is a relationship that there must be less of the initial reactants than products, thus a ratio of reactants to products is useful
equilibrium constant (k)
a quantitative expression of the distribution of reactants vs products for a system at equilibrium
k = 1
a 50:50 distribution of P and Rs
k < 1
reactant concentration is greater than product concentration
k > 1
product concentration is greater than reactant concentration
concentration values used in k
solutions: molar concentrations (M)
pure liquids or solids: 1 (H2O = 55.5M)
gases: partial pressure (p*atm)
how constant is k?
initial reactant concentration- no effect on k
pressure – no effect (except gases)
catalyst- no effect on k
temperature- does effect k; k is dependent on T
Neutralization Reaction Summary:
Strong acid with strong base –
weak acid with strong base-
strong acid with weak base-
Strong acid with strong base- pH = 7.0
weak acid with strong base- pH > 7.0
strong acid with weak base- pH < 7.0
pH for CH3COOH
8.72 pH
main differences between strong acid and strong base versus weak acid and strong base (3)
1) weak acid & strong base starts at a higher pH
2) inflection point is harder to hit with a weak acid & strong base
3) equivalence point is greater than 7.0 with a weak acid & strong base
Le Chatelier’s Principle
1884
if stress is applied to a system in equilibrium, the system will behave in a manner that relieves the stress to restore equilibrium
concentration
increase in concentration increases the rate of the reaction, so an increase in reactants –> R
temperature
rate of the reaction increases about 2x for each 10C increase in temperature
exothermic reactions
evolve heat since less energy is involved in bonds joining the product atoms together than required to bond reactant atoms
endothermic reactions
absorb heat so forward reactions are favored when heat increases. this is due to more energy being required for forming the product bonds
pressure
rate only effected when the reactants or products are gases. So an increase in pressure is equivalent to the increase in concentration.
catalyst
though it is a reaction enhancer, there is no effect on reactant, so no effect on k
in the spectrophotometic analysis of commercial aspirin lab we used _____ to analyze the percent composition of commercial grade aspirin
visible electromagnetic radiation, or white light
Plank relationship equation
E = hv
wavelength
distance between two crests of a wave
frequency
the number of crests passing a given point in space each second
wavelength is usually measured in
Angstroms ( 1A = 10^-10 m)
polychromatic light
white light, or sunlight, composed of wavelengths of various colors
monochromatic light
light of a single wavelength
when white light comes in contact with an object it may be
1) reflected by
2) absorbed by
3) transmitted through
light transmitted or reflected through an object will appear as
the complementary color
Beer’s Law equation
A = abc
A: absorbance
a: molar absorptivity
b: path length
c: concentration
in Le Chat lab, the solution with the darkest color has the
highest concentration of FeSCN2+
rate-controlling step
the slowest step in the mechanism
molecularity
number of particles that collide
in the Kinetic Study of an Iodine Clock Reaction lab, the order of reaction and the specific rate constant, k, was determined by
the Method of Initial Rates
In the Kinetic Study of an Iodine Clock Reaction lab, the presence of I2 is detected by
observing the deep blue color it forms with the starch indicator
In the Determination of an Equilibrium Constant lab, why is the cork wrapped in foil
to block the gas from escaping through the cork’s large pores
Decantation
The separation of a liquid from a solid by careful pouring, allow the solid to settle to the bottom of the container.
Extraction
A separation process used when only one component of a mixture is soluble in a specific added solvent. After adding the solvent, the insoluble components can be recovered by removing the solvent using decantation or filtration.
Why is water capable of dissolving other substances?
The reason for it is because of waters highly polar nature. The electrons in a water molecule aren’t distributed equally but are concentrated near the oxygen atom and less concentrated near the hydrogen.
Electrolyte
A substance that conducts electricity when dissolved in water. Strong electrolytes conduct strong ions whereas weak electrolytes do not.
Solubility
The maximum mass of a solute that can dissolve in a mixture.
Miscibility
When both solute and solvent are liquids