AP Chem Semester 2 Final Flashcards
How do you find the rate for one component of a reaction from another?
You apply the stoichiometric coefficient
What is the sign of rate?
Rate is always positive
How can you find rate?
You can find it numerous ways depending on the problem
One way is using the change in concentration/change in time, but this only works if rate is constant.
If given a tangent line to the rate curve can you find the instantaneous rate?
Yes you can as the tangent line represents the slope at that point.
What is the reaction order of a molecule?
It is the exponent that decides it’s relationship to the rate. So for
Rate = [Product]^2 the rate order is 2.
How can you determine the reaction order of a substance experimentally?
Double the concentration of the substance, and see how the reaction rate changes.
What are the integrated rate laws for each common order and their corresponding half life formula?
All integrated rate laws take the form -kt + The first statement below.
Zero Order: [Concentration], [Concentration]/2k
First Order: ln([Concentration]), 0.693/k
Second Order: 1/[Concentration], 1/(k*[Concentration])
What is the Arrhenius equation and its constants/variables?
k = Ae^(-E/(R*T))
where A is the frequency factory, E is the activation energy, T is the temperature in Kelvin, and R is the ideal gas constant 8.314.
How can you determine the order of a reaction using a graph?
Look at the half life and see what order it aligns to
How do you find the rate law given the mechanisms if a mechanism which is not the first step is the RDS?
Assume equilibrium for previous steps and solve for the intermediate
How do you classify number of molecules of a given step?
1 reactant -> Unimolecular
2 reactants –> Bimolecular
3 reactants –> Termomolecular
What are the elements of the frequency factor?
Orientation factor p
Collision frequency z
A = p * z
What is an elementary step?
it is any step that composes an overall reaction that can not be broken down into more steps
What is the difference between heterogeneous and homogeneous catalysts?
Heterogeneous catalysts are in a different phase than the reactants, and homogeneous catalysts are in the same phase as the reactants
What is dynamic equilibrium?
The idea is that equilibrium is reached not because the products and reactants are no longer doing forward and backward reactions, but because the rate of the reactions is the exact same.
What is the law of mass action?
For a balanced equation aA + bB -> cC + dD
The equilibrium constant is
K = (C^cD^d)/(A^aB^b)
This is only true at equilibrium
What do different values of K mean?
High K means products aka forward reaction is favored, Low K means reactants aka reverse reaction is favored
What are the rules of K algebra when modifying equations?
If reversing an equation K_new = 1/K_old
If multiplying an equation by n K_new = K_old^n
If adding two equations together K_new = K_old1*K+old2
How do you convert from K_c to K_p?
K_p = K_c*(RT)^(c+d-a-b)
What is the assumed units of K_p
atm
What do you and don’t you include in an equilibrium expression?
Solids and Pure Liquids are not included, Gasses are and Aqueous solutions are
What is Q and how can you use it’s relationship to K to predict change in a system?
Q is the result of the law of mass action equation whenever the products and reactants are not at equilibrium (Note if there are not reactants q isn’t undefined it is infinity). This means Q can be gotten at any point, not just equilibrium.
If Q < K then the reaction will shift right
If Q > K then the reaction will shift left
If Q = K the reaction is at equilibrium
How do you find equilibrium with only the initial concentrations?
Use and ice table
What is a good method for simplifying a equilibrium problem and what is the tolerance for this method?
You can use an x is small approximation
x/(value it was supposed to be subtracted from ) * 100% should be less than 5% for this approximation to be valid
What is the effect of changing volume on equilibrium?
Decreasing the volume causes the reaction to shift in the direction that has the fewer moles of gas particles.
Increasing the volume causes the reaction to shift in the direction that has the greater number of moles of gas particles.
If a reaction has an equal number of moles of gas on both sides of the chemical equation, then a change in volume produces no effect on the equilibrium.
Adding an inert gas to the mixture at a fixed volume has no effect on the equilibrium.
How does temperature effect equilibrium?
In an exothermic chemical reaction, heat is a product.
Increasing the temperature causes an exothermic reaction to shift left (in the direction of the reactants); the value of the equilibrium constant decreases.
Decreasing the temperature causes an exothermic reaction to shift right (in the direction of the products); the value of the equilibrium constant increases.
In an endothermic chemical reaction, heat is a reactant.
Increasing the temperature causes an endothermic reaction to shift right (in the direction of the products); the equilibrium constant increases.
Decreasing the temperature causes an endothermic reaction to shift left (in the direction of the reactants); the equilibrium constant decreases.
What is deltan for a equilibrium equation?
For a balanced equation aA + bB -> cC + dD
deltan = c+d-a-b
What are the general properties of acids and bases?
Acids have the following general properties: a sour taste, the ability to dissolve many metals, the ability to turn blue litmus paper red, and the ability to neutralize bases.
Bases have the following general properties: a bitter taste, a slippery feel, the ability to turn red litmus paper blue, and the ability to neutralize acids.
What is the Arrhenius Definition of acids and bases?
An acid is a substance that produces H+ ion in an aqueous solution
A base is a substance that produces OH+ ions in an aqueous solution
What is the Bronsted Lowry definition of acids and bases?
Acids are proton donors and bases are proton receivers
What are the 7 strong acids?
Hydrochloric (HCl), Hydrobromic (HBr), Hydroiodic (HI), Nitric (HNO_3), Perchloric (HClO_4), Sulfuric (H_2SO_4), Chloric HClO_3
What causes strong and weak acids?
The strength of the attraction between the hydrogen molecules and whatever A^- group it has. The weaker the attraction the stronger the acid
How do you find K_w given an alternative concentration of H_3O+?
Since sqrt(K_w) = [H_3O+] = [OH-] you can just square H_3O+
How do you find pH, pOH, and [OH-] from [H_3O+]
pH = -log[H_3O+]
pOH = 14-ph
OR
[OH-] = 10^-14/[H_3O+]
How does pKa relate to acid strength?
The smaller the pKa, the stronger the acid
How do you calculate the percent ionization of a weak acid?
% ionization = [H_3O+]_equil/[HA]_initial * 100%
How do you find the H_3O+ concentration for different acid solutions?
Strong Strong
Sum the cocentrations of the strong acids
Strong and Weak
Just treat it like a strong acid problem, ignoring the weak acid
Weak and Weak
Find the stronger of the two weak acids, and if it is sufficiently different just treat it as a problem with only that acid. The idea since it is sufficiently stronger it will prevent the formation of H_3O+ from the other one.
How do oxygens affect acids?
More oxygens generally means a stronger acid as it further polarizes the central element causing in turn for that element to further polarize and weaken the OH bond. So for example H_2SO_4 will be more acidic than H_2SO_3.
However, in some cases, having no oxygens is stronger. For example
HBr is stronger than HBrO2
What should you always remember regarding pH?
Higher pH is more basic, not more acidic
What is hydroxide and what is hydronium?
Hydroxide is OH-, Hydronium is H_3O+
How do you deal with base solutions?
The same as you would handle acid solutions
What are the acid base properties of salts?
Anions (negative charge) generally act as weak bases, with the conjugate base anion of a strong acid being a negligible base
Cations (positive charge) generally act as weak acids, with the conjugate acid cation of a strong base being a negligible acid
Additionally, some highly charged metals such as Al and Fe with a 3+ charge can act as a weak acid because their hydrated forms act as a weak acid.
How do you deal with diprotic solutions?
Simply do two consecutive problems, plugging the numbers from the previous table into the next one.
In many cases, you can disregard the second step as the K_a is significantly smaller than the first step
Why are certain substances acidic?
Because of a polar bond they form with hydrogen which causes it to have a positive charge
What is the lewis model of an acid and why is it important?
The lewis model of an acid simply defines an electron pair acceptor and a base as an electron pair receiver. This make it so that substances that don’t even have a hydrogen molecule can be considered an acid. For example, BF_3, CO_2, and Al^3+/B^3+ could be considered an acid. A common lewis acid is an element with an incomplete octet
How do you find the pH of a buffer solution without Henderson Hasselbach?
Set up an ice table, but both the acid and the conjugate base have an initial concentration
What is the henderson hasselbach equation?
To find the pH of a buffer solution we can multiple approximations
- x is small
- the equilibrium concentration of the acid and base will be roughly equal to the initial concentration
from this we simplify the quadratic to
pH = pKa + log(base/acid)
Always ensure x is small is valid
What are the rules of Hess’s law?
If you reverse the reaction multiply G/H by -1, if you multiply a reaction by a coefficient multiply the G/H by that coefficient, if you add the equations add H/G together.
For a general method look for a shopping list of the stuff in the base equation.
Remember that reactants cancel out products and vice versa. So if you have NO + O_3 -> NO_2 + O_2 and want to get NO + O -> NO_2
You would want to use a formula with O_3 on the products side to cancel it.
What are the conditions for a buffer to be effective (aka the range)?
The ratio of base to acid must not exceed 10 or go under 0.1. Aka the range is (pKa-1, pKa+1)
How do you calculate the change in a buffer is an acid/base is added?
Find the number of mols of acid and base that the solution has, subtract mols from one and add it to the other based on the mols of acid or base added, do henderson hasselbach again
How do calculate percent change in a buffer?
Change in pH/original pH
What is buffer capacity and what are its rules?
Buffer capacity is the amount of acid or base that can be added without causing a significant change in pH for the buffer. The greater the absolute concentration (aka the higher the molarity) the greater the buffer capacity. Overall buffer capacity also increases the closer the relative concentrations of the components become more similar
What are the important points of a pH curve and how do you find them?
The initial point, found by doing an ICE table,
The half equivalence point, where pH = pKa and the volume of acid or base added is half of the equivalence point
The equilvalence point, where the number of moles of reactant (acid or base) is equal to the number of moles of the acid or base being used to titrate it
IMPORTANT Why does being at the equivalence point not necessarily mean being neutral?
For strong acids it does cause their conjugate base is negligible. However, for weak acids it does not because it complete converts them to their conjugate base, which after applying an ice table make them basic.
What is an important thing to remember when titrating?
The titrant has volume, so when calculating the molarity of hyonium you must divide by not just the original volume, but additionally the volume of titrant added.
How do you do a basic acid base problem?
Set up the acid base equilibrium equation
HA + H_2O -> A^- H_3O+
Then use K_A = [A-][H_3O+]/[HA]
and solve.
This can be done in reverse for the conjugate base by just doing
K_b = K_w/K_a
And then solving
K_b = [HA][OH^-]/[A^-]
How does polyprotic acid titration differ?
There are two equivalence points
What is K_sp and how do you make a formula for it?
For an equation AB[s) -> aA(aq) + bB(aq)
The equation for K_sp is
K_sp = [A]^a[B]^b
IT IS EXTREMELY IMPORTANT TO REMEMBER TO OMITS SOLIDS HERE
How do you find S from K_sp
For an equation AB[s) -> aA(aq) + bB(aq)
With the balanced equation written, we note that A will increase by aS and B will increase by bS, and both will start with no concentration (in a standard problem)
You can then write out K_sp = [aS]^a[bS]^b
And solve for S
What is S vs K_sp?
S is the molar solubility and K_sp is the solubility product constant
How do you account for a common ion?
Include it in the table as the initial concentration
What is the affect of pH on solubility?
Just remember that acidic solutions will neutralize OH- and basic solutions will neutralize H_3O-, causing the reaction to shift accordingly.
How does precipitation work?
When Q (the reaction quotient) is greater than K the solution is super saturated and will begin to precipitate. This means if you mix two things in a solution, and solve the solubility equation, and Q is greater than K, a precipitate will generally form. You can also use this method to find when something would begin precipitating.
How does selective precipitation work?
Imagine you have Mg^2+ and Ca^2+ in a solution, which can form Mg(OH)_2 and Ca(OH_2) respectively. Since one of those has a different solubility product constant than the other you can find the concentration of OH that would precipitate one but not the other by backsolving the solubility equation
IMPORTANT: You generally want a K_sp difference of at least 10^3 for selective precipitation
What are pH ranges and colors of phenothelein, bromothymol blue and litmus indicators?
From low ph to high ph
phenothelein 8 to 10, White to Red
bromothymol blue 6 to 7.5 Yellow to Green to Blue
litmus indicators 0 to 14, rainbow order
What are spontaneous vs nonspontaneous processes?
Spontaneous processes occur will occur without energy being put into the system. An example of this is rusting
Spontaneous processes require energy to get put into the system to occur
What drive spontaneous processes?
The world likes to become more disorderly.
How do you calculate S?
S = kln(w) where k is the boltzmann constant 1.38*10^-23
When do you use ln rather than log?
Boltzmann S equation, reaction quotient for non-standard gibbs state, for non-standard e-cell state
KEEP WRITING MORE SHIT IN THIS
What should you always remember when calculating G?
Generally S can be in J and H can be in kJ so make sure to convert
What is a macro vs micro state?
A macro state is the overall state of a substance, a microstate is the exact state of each and every particle at a given snap shot of time.
How can you find the number of microstates of gas particles in two bottles?
Count up the different positions each particle can take.
IMPORTANT Each particle should be considered unique, so the state 1,2 | 3,4 is not the same as 2,3 | 1,4
HOWEVER
The number of particles in a given bottle should be considered its own macro state, so a split of 2 | 2 is different than 4|0
What is S for state changes?
What is a reversible reaction in the context of entropy? How do calculate changeS for a such a reaction?
Any reaction where an infitessimally small change in a property can change the direction of the reaction For example water at 0C
changeS = q_rev/T
where q_rev is the heat exchanged with the surroundings in Joules and T is the temperature in kelvin
You can find q using H_rxn by multiplying H_Rxn by the number of mols that are reacting.
OR
changeS = -changeH_system/T
What should be remembered about temp
ALWAYS IN KELVIN
What is the effect of temperature change on entropy? How does this affect endothermic vs exothermic reactions?
Higher temperature generally means higher entropy, lower temperature generally means lower entropy?
Endothermic reactions will thus reduce the entropy of the surroundings
Exothermic reactions will thus increase the entropy of the surroundings
How do you calculate gibbs free energy?
G = H - TchangeS
Where H is the enthalpy, T is the temperature in KELVIN, and S is entropy
REMINDER HERE AGAIN
S is generally in J/k and H is generally in kj, so you MUST and I mean MUST divide the S part by 1000
How can predict spontaneity using entropy?
A reaction is generally spontaneous is entropy is positive and nonspontaneous if it is negative.
How can we predict spontaneity using gibbs free energy?
A decrease in gibbs free energy means a spontaneous reaction, an increase in gibbs free energy means a nonspontaenous reaction
What is the standard state for liquids, solids, gasses, temperature, and aqueous solutions?
For a Gas: The standard state for a gas is the pure gas at a pressure of exactly 1 atm.
For a Liquid or Solid: The standard state for a liquid or solid is the pure substance in its most stable form at a pressure of 1 atm and at the temperature of interest (often taken to be ).
For a Substance in Solution: The standard state for a substance in solution is a concentration of 1 M.
How can we find S, G, and H using standard S’s?
For a formula aA + bB -> cC + dD
Let U represent the given standard we’re using whether than be S,G, or H
dU_D + cU_C - aU_A - bU_B
More generally
S/G/H_rxn = nS/G/H_products - nS/G/H_reactnats
What properties of a molecules effect entropy?
Weight The heavier the element the greater its entropy generally
Complexithy The more complex an element the greater its entropy generally
Symmetry The less symmetrical an element the greater its entropy generally
Dissolution If a material is dissolved in water it will generally have a greater entropy
Allotrope The less constrained an allotrope is the greater the entropy
What is the equation for gibbs energy in a non standard state?
For a formula aA + bB -> cC + dD
Gibbs Free Energy = G_rxn _standard + RTln(Q)
where Q is the reaction quotient
Q = Products/Reactants
for the example formula Q = (C^c * D^d)/(A^a * B^b)
What is the relationship between G and K?
G = -RTln(K) AT EQUILIBRIUM
What is H equal/proportional to?
H = -S_surroundings*T (remember in the G equation the S is the S of the system)
What are the oxidation state rules?
The sum of the charges which compose a molecule must add up to the charge on that molecule (0 if there is no charge)
You can figure out charge by applying these rules
Group 1 Metals are always + 1
Group 2 Metals are always + 2
Oxygen is always -2 unless it is forming F_2O
Hydrogen is always + 1 except in metal hydrides
Fluorine is always - 1
Chlorine is always -1 except in the presence fluorine or oxygen
How do you balance a redox equation?
There is two methods, either brute force, or break the equation into the reduction and oxidation part, and apply stoichiometric coefficients to balance
What is a voltaic cell?
A voltaic cell is a cell which transfers electrons from the anode to the cathode using a spontaneous reaction to create a flow of electricity
What is electrochemical cell notation?
Anode on the left of the double line, Cathode on the right of the double line. To the left of the single line in each is the reactants, and on the right is the products
Inert substances used go on the right
How do you find the anode and the cathode based on electric cell potential?
The lower electric cell potential will be oxidized and the higher electric cell potential will get reduced.
You find the E_cell by doing the following
E_cell = E_cathode-E_anode
How can you use E to predict spontaneity?
E is positive for spontaneous reactions and negative for nonspontaneous reactions
What is SHE and how is it used?
SHE is standard hydrogen electrode. It is a reference point by which all other electric cell potential is based on.
What is relationship between G and E_cell
G = -nFE_cell
Where n is the number of electrons transferred in the balanced equation and F is faraday’s constant 96485.
What is relationship between E_cell and k?
E_cell = ((RT)/(nF)) * ln(K)
How do you find E_cell using the nernst equation under nonstandard conditions?
E_cell = E_cell_standard - ((RT)/(nF)) * ln(Q) where Q is the reaction quotient
How do find the amount of something that can be plated given a current and an amount of time?
Take the current and multiply by the amount of time to get the number of coloumbs,divide this by 96485 C/mol of e to get the mols of e that are transfered. From there divide by the number of mols of electrons transfered during the described process. Since you know how many times the reaction occurred you now have the number of mols of product, multiplied by the molar mass gives you the amount plated.
What are the different functional groups, their postfixes, and their identifiers?
Alkene, -ene, carbon double bond
Alkyne, -yne, carbon triple bond
Alcohol, ol, bond to an OH group
Ether, ether, two carbon not bonded to each other but connected by their bonds to an oxygen
Ketone, one, two carbon not bonded to each other but bonded to a different carbon that has an oxygen double bond.
Phosphate, (either mono or di depending on the amount of goups, 4 Os attached to a P
What are the common alkane names in order from one carbon, all the way up?
Methane, Ethane, Propane, Butane
And from there just the prefix for the number of carbons followed by ane.
What is isomerism in hydrocarbons?
Different hydrocarbon formula, despite being identical empirical formula wise, can be entirely distinct base on the placement of the carbon
What is a hydrocarbon chain called when a single one of its hydrogens is removed?
It becomes an alkyl group
Name of the number of carbons attached to the carbon where hydrogen is being removed (nothing for 1, sec for 2, tert for 3, quat for 4) + hydrocarbon + yl + group
So methane becomes a methyl group
NOTE
The number of carbons attached thing only applies for a hydrocarbon with number of C >= 4. For propane if the middle atom has a hydrogen removed it is isopropyl
What are some properties of hydrocarbons?
They are largely inert other than under specific conditions involving oxygen
Boiling and Melting point increases as their weight increases
Increasing branching reduces boiling point
Less dense than water
No smell
Not high density
How do you name an alkane?
It takes 5 steps
1.
Identify the longest chain of carbon in the molecule. If there are equal length chains pick the one that has more branches
2.
Number the atoms in the longest chain starting at the ends from 1. The carbon labeled 1 should be at the end closest to the first branching point. If both ends are equidistant from a branching point start with the one closest to a second branching point.
3.
Identify the substituents at the branching off points, and attach a number to them according to where they are attached to the longest chain. So for example if a methyl group was attached to the carbon labeled 4, you would call is 4-methyl.
- Write all the substituents in alphabetical order followed by the name of the main chain. If multiple of the same substituent are present at different points take the numbers and list them with a comma in between, followed by the group with a prefix of di,tri,tetra,hepta, and so on. This pre-fix should not be considered when placing them in alphabetical order.
- In cases with a branched alkane within a branched alkane, place paranthesis around the substituent branched alkane and treat it as its own problem. Then, outside the paranthesis write the place of it in the main carbon chain. It is alphabetized according to the first letter of it, including numerical prefixes.
