Exam 2 Flashcards
Lectures 17-26
Osmosis
selective passage of solvent molecules through a porous membrane from a more dilute solution to a more concentration one
* solvent flows from more dilute solution to a more concentrated one
Osmotic pressure
pressure required to stop osmosis
Hypotonic solution
has a lower concentration of particles than the cell
What happens if a cell is placed in a hypotonic solution
water (solvent) rushes into cell, cell swells, and bursts
Hypertonic solution
has a higher concentration of particles than the cell
What happens if a cell is placed in a hypertonic solution
water moves out of the cell, causing it to shrink
Balancing equations (4 points)
- if only C, H, O in equation, balance it in that order
- balance a free element at the end
- balance a metal before a nonmetal
- don’t seperate polyatomic ions
Combustion
reactant: oxygen
product: CO2 and H2O
rate
how much a quantity changes in a given time
thermodynamics
whether free energy was released or absorbed
collision theory
collision frequency
collision energy
collision orientation
What are the 4 factors that affect rate?
- concentration of reaction
* direct - temperature
* direct - physical state
* 2 liquids = more collisions
* 1 solid 1 liquid = less - catalyst
* not consumed
* only small amount needed
orient molecules so correct orientation is greater
For each __ rise in temp, the rate of reaction __
10 degrees celcius
doubles
rate expression
gives relationship between the different rates of change of reactants and products of the same reaction
* reactions are negative
* products are positive
differential rate law
relationship between rxn rate and reacatant concentration
Which factor affects k?
temperature
Which factor does not change k?
concentration
How do you find order of the reaction?
add the exponents of the reactants
Sign for rate of appearance and disappearance
appearance=+
disappearance=-
Half-life
time it takes for half the substance to disappear
relationship between order for half life and concentration
0 - direct
1st - no relationship
2nd - inverse
zero order half life gets longer or shorter, why
half life gets shorter with time
rate is constant, so it takes shorter time to make substance disappear
For first order half life, which factors depend on concentration and which ones don’t
depend on concentration: rate *rate=k[A]
does not depend on concentration: k and half-life
Second order half-life gets longer or shorter, why
half-life is getting longer with time because it is dependent on collision, and lower concentration means less collusions
activation energy
minimum amount of energy to START a reaction * lowest activation energy is most stable and fastest
transition state
when molecules collide effectivelt, they form an activated complex
* partially broken and partially formed bonds
* unstable
* transitional species: partly between reactant and product
How do you find the overall order of the reaction?
add the exponents of the reactants
remember
- check if the equation is balanced
- don’t forget k in rate
- for elementary reactions (NOT overall reaction), the order can be determined from the coefficients
- if it says “second decay”, you have to do it twice
- include units for k
- some equations line up with y=mx+b
- make R into kJ if needed
sig fig rule with logs
sig figs in answer after decimal point is the same number of sig figs in log
ex. log 4.000 (4 s.f.) = 0.6021(4 s.f. to right of the decimal point)
integrated rate law
used to determine how long a reaction takes or how much reactant or product is present at a given time
key words to know to use the integrated rate law
“How long”
frequency factor
of collisions with correct orientation to react
how does temperature affect half life of radioactive decay vs chemical reactions
doesn’t affect half life of radioactive decay
affects half life of chemical reactions
catalyst
consumed then produced
intermmediate
produced then consumed
unimolecular
reactant is 1 molecule
bimolecular
reactant is 2 molecules
termolecular
reactant is 3 molecules
Which molecules are in the rate law?
molecules that are in the overall equation
3 conditions to validate a mechanism
- sum of elementary reactions must equal overall balanced equation
- rate law for slow step can’t have any intermmediates (if slow step is first, it will never have intermmediates in the rate law b/c intermmediates are produced then consumed (products aren’t included in the rate law; however, if the slow step is not the first step, it could have intermmediates)
- slow step must have same rate law from experimental data
When do you vs do not subsitute?
- substitue when there is a fast initial rate followed by slow step w/ intermmediates
- don’t substitute when there is a slow initial step w/ intermmediates
2 conditions to check when writing the overall rate law
- if the molecules are included in the overall equation, include it in the rate law
- is the slow step first w/ intermmediates? if not first step w/ intermmediate, need to substitute
intermmediates
not reactants or products
catalysts
- increase rate of forward and reverse reactions
- a catalyzed rxn yields the product more quickly but it’s the same amount of product
enzymes
- biological catalyst
- most are proteins
*bind substrate (reactants) in active site and orients it for rxn
*highly specific
(1 enzyme: 1 reaction) - doesn’t alter amount of energy consumed
How do enzymes attract and hold substrate?
weak non-covalent interactions ex. hydrogen bonding, hydrophobic interactions, ionic interactions
lock and key model
- enzyme = lock
- substrate = key
Why is the lock and key model not the best model
the substrate has to fit perfectly for the enzyme to work
* if no strong interactions, enzyme and substrate complex will fall apart so no products will be produced
induced fit enzyme model
- active site is flexible pocket whose shape changes to accomodate substrate molecule
- after, product doesn’t fit in active site and is released
binding energy
free energy released in forming multiple weak bonds + interactions between an enzyme and its substrate
How do enzymes lower activation energy?
*puts molecules in close proximity to react and collide
* analogy: wingman
saturated
so much substrate that the rate is limited by enzyme availability; all active sites are occupied
competitive inhibitor
competes w/ substrate for active site on enzyme and is a similar structure as the enzyme
* solution: increases concentration of substrate because this increases chance
noncompetitive inhibitor
bind to location other than active site, changing shape of enzyme; substrate can’t bind to enzyme anymore
* solution: move inhibitor
irreversible inhibitor
inhibitors covalently change active site permanently
* solution: wait for more enzyme
what stays the same in competitive inhibition
Vmax
what stays the same in non-competitive inhibition
Km
Lineweaver-Burk plot
* x-axis (units)
* y-axis (units)
* x-intercept
* y-intercept
x-axis: 1/[S] (m/M)
y-axis: 1/V (1/micro moles)
x-intercept: -1/Km
y-intercept: 1/Vmax
Michaelis-Menten plot
* x-axis (units)
* y-axis (units)
* x-intercept
* y-intercept
- x-axis: [S] (mM)
- y-axis: V (micro moles)
- x-intercept: Km
- y-intercept Vmax
emission
particles goes on right side of arrow
* emission means release
* look for “decay”, “production”, “formation”
capture
particle goes on left side of arrow
* look for “absorption”, “bombardment”
gamma decay
no particles emitted
What order is radioactive decay?
1st order
how does length half-life length affect temperature
shorter half-life means more nuclei decay every second which means hotter
does temperature affect rate of change in radioactive decay
no
How to find grams of excess reactant?
substract moles of product, do moles to moles of excess reactant and convert that into grams of the excess reactant
from a graph, how do you know which step is the rate-determining step and how do you know the intermmediates
*the one with the highest activation energy
* the bumps are the steps, so look at which bumps the intermmediate is in between
what is the slope for differential and integrated rate law
order and half life
- 0 = half life decreases over time
- 1st = half life remains constant
- 2nd = half life increases over time
how to write the rate law when there are 3 reactants
hold the other 2 reactants constant
