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From Flashcardlet > AP Chem Ch 11-12 > Flashcards

AP Chem Ch 11-12 Flashcards

0
Q

Molality

A

m = mol solute / kg SOLVENT

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1
Q

Molarity

A

M = moles of solute / L of solution

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2
Q

Normality

A

N = nM

Where n = # H+ in acids, #OH- in bases, #e- in redox

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3
Q

% solute

A

Mass solute / mass solution

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4
Q

Mole fraction

A

X solute = moles solute / total moles

X solvent = moles solvent / total moles

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5
Q

Enthalpy of solution

A

Delta H sol =
Delta H 1, expand solute +
Delta H 2, expand solvent +
Delta H 3, combine the solute and solvent
Both Delta H 1 and delta H 2 are positive because they require energy.
Delta H 3 will be negative for like and like solute and solvent, it’ll take more energy for nonlike solute and solvent to dissolve

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6
Q

How enthalpy of solution explains polar-polar and polar-non-polar dissolving rules

A

For a polar-polar solution, delta H1 and delta H2 are both positive, but delta H3 is negative, making the overall enthalpy of solution just slightly positive, making it favorable as it is more probable to find a solution in water in its aqueous state when the energy isn’t that large (entropy)

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7
Q

Factors affecting solubility:

1. Structure effects

A

Hydrophobic - water fearing, non polar
Hydrophilic - water loving, polar
Like dissolves like, so hydrophilic will dissolve in water

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8
Q

Factors Affecting Solubility:

2. Pressure effects

A

Dissolving a gas into a liquid– Henry’s Law
Push the piston in, increase pressure, THIS then increases the number of gas molecules per unit volume. Increases rate gas enters the solution, so concentration of dissolved gas increases. Greater gas concentration causes an increase in rate of escape
Henry’s Law

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9
Q

Henry’s Law

A

C= kP where k is a constant, P is the partial pressure of the gaseous solute above the solution. C is the concentration of the dissolved gas
Gas dissolved in a solution is directly proportional to the pressure of the gas above the solution.
Increase pressure, increase number of gas molecules per unit volume and the gas enters the solution at a higher rate than it leaves

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10
Q

When does Henry’s Law not work?

A

Not ideal for ionic substances that dissolve. Use the Vant Hoff factor

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11
Q

Factors Affecting Solubility:

Temperature

A

Dissolving of a solid occurs more rapidly as temperature increases, however the amount doesn’t correlate to the temp.
No general correlation between T and Solubility for solid or liquid.
For gas, Solubility decreases with increase in T
KE up, Boltzmann –> more equivalents with enough energy to be in gas phase, so less dissolves.

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12
Q

Vapor pressure of solutions (experiment with water and aqueous solution in dome)

A

Place a beaker of pure water and a beaker of an aq solution in a closed environment. Water will be transferred to the solution, as the vapor pressure of the pure solvent is > the VP of the solution.
The net effect is a transfer to our solution to achieve equilibrium.
The prescense of a solute thus lowers the vapor pressure of a solvent.

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13
Q

Raoult’s Law

A

P solution = X SOLVENT * P not solvent
X solvent is the mole fraction of the solvent, moles solvent / total moles.
P not solvent is the expected VP of solvent at given conditions
Works for ideal solutions, but for something like NaCl with I = 2, the vapor pressure decreases two times the expected amount because two ions.

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14
Q

Raoult’s Law for ionic solutes

A

Say we have NaCl dissolving in water. 1 mol of NaCl and 10 mol of water would give X 10/11, but multiply 1 by 2 because I = 2 to get a new X proportion of 10/12

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15
Q

Ideal solutions

A

Solvent-solvent interactions similar to solvent-solute similar to solute-solute
Raoult law works for ideal solutions like ideal gas law does for ideal gases
Can deviate in positive or negative direction

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16
Q

Negative deviation from Raoult’s Law

A

When the VP decreases more than expected. For example, H-bond IMFS. Coincide with large - Delta H solution.

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17
Q

Positive deviation from Raoult Law

A

Weak solute-solvent interactions

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18
Q

Raoult’s Law for liquid-liquid solution

A

P total = PA + PB =

XA * P NOT A + XB*P NOT B

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19
Q

Colligative properties

A

Properties that depend on the number of, not the identity of, solute particles in an ideal solution

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20
Q

Boiling point elevation

A

Normal boiling point of a liquid occurs at the temperature when the vapor pressure = 1 atm. Solute lowers the vapor pressure, so need to heat to a higher temperature to get to 1 atm.
So, a nonvolatile solute elevates the boiling point of the solvent.
Delta T = i * kb * m
Where I is the vant hoff factor, kb is the boiling constant, and m is the molality

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21
Q

Freezing point depression

A

Freezing point lowers when a solute present because the water in the solution has a lower vapor pressure than that of pure ice. So, no ice can form. Need to lower the temperature until the vapor pressure of the solution equals the vapor pressure of the ice.
Delta T = i * kf * m (solute)

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22
Q

Osmosis

A

The movement of water molecules from high to low concentration

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23
Q

Semi permeable membrane

A

Small molecules of water can move through but larger ions cannot

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24
Q

Osmotic pressure

A

The minimum pressure that stops the osmosis
The volume of the solution increases while the volume of the solvent decreases. At equilibrium, there is a greater hydrostatic pressure on the solution than on the pure solvent. Excess pressure is the osmotic pressure.
Pi = iMRT
Where I is vant hoff factor, M is molarity of the solution, R is constant (.0821) and T is temperature in Kelvin

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25
Q

Isotonic solutions

A

Solutions with identical osmotic pressures

26
Q

Hypotonic solutions vs hypertonic

A

Hyper is more solute, hypo is less solute

27
Q

Vant hoff factor

A

I, the number of ions, always needs to be included in the colligative property equations

28
Q

Colloids

A

Suspension of tiny particles in some medium

29
Q

Tyndall effect

A

Light scatters in a colloid but not in a pure substance

30
Q

Nitrogen cycle

A

From the Nitrogen cycle, the Haber Basch Mitasch process, we see how important reaction rates are, as we need to get the reactions done in order to feed the human population

31
Q

High temperature favors what side?

A

Increase temp, increases rate, also pushes equilibrium to favor the reactants (increased temperature favors the side of the reaction with more gas molecules)

32
Q

What side does increased pressure favor in a rxn

A

Favors the products (higher pressure favors the side of the rxn with fewer gas molecules)

33
Q

Kinetics

A

The study of reaction rates

34
Q

Rate

A

The change in a given quantity over a specific period of time
GOAL is to understand the steps by which a rxn is taking place or the rxn mechanism

35
Q

How to calculate rate from graph showing concentration vs time

A

Change in molarity / change in time
That’s the rate at a given time
Use integrated rate laws to get concentration depending on time

36
Q

How do rate and concentration and time influence each other?

A

For non-zeroth order reactions, as time goes on, there is less concentration of the starting material, and collisions are thus less likely to occur, so it takes longer for the rxn. The rate decreases as time goes on and concentration lowers

37
Q

Rate law general equation

A

Rate = k* [A]^n
K is the rate constant, differs for each reaction
N is the order of the reaction, determined experimentally
If more than one reactant, rate = k* [A]^n * [B]^m
Note: need to do initial rates to not use reverse reaction

38
Q

Differential rate law vs integrated rate law

A

Differential shows how the rate of a reaction depends on concentration. Rate = k [A]^n
Integrated rate law shows how the concentration of species in the reaction depend on time.

We study under conditions where reverse reaction is not important – just use reactant concentrations

39
Q

How to determine order of reaction given M and times?

A

Need to plot the data (M vs Time) and get the tangent line at the given point – that’s the rate
If can’t graph, then
If no correlation between M and time, then zeroth
If ln[A] and t produce a linear relationship, then first order
If 1/[A] and t produce a linear relationship, then second order

Can also do slope and see if get same values for different values (pick three points and make sure get same slope when subtract each)

40
Q

How to determine order of reaction given initial concentrations and initial rates? (Method of initial rates)

A

Pick experiments when A has same concentration and B has different
Then rate 2/ rate 1 = [B2]^n / [B1]^n
Plug in and find n
Then do same where b stays same and A changes, and calculate p
Then plug into overall equation – rate = k [A]^p * [B]^n
And calculate k plugging in data from any experiment

41
Q

Overall order of reaction

A

Sum of the individual orders

42
Q

Integrated rate laws

A

How the concentration depends on time. Concentration as a function of time

43
Q

Integrated rate law equations

A

1st and 2nd order are on the reference table –>
1st is with ln vs r and second is with 1 / [A] vs t

Zeroth –>
[A] = -kt + [A0]
[A] vs t

44
Q

Half life

A

Time required for a reactant to reach half its original concentration

45
Q

How to calculate half lives given integrated rate law equation

A

Half life is when half the substance is left, so [A]t = [.5A0]. Plug that in for [A]t and we can then calculate t in terms of k (in terms of A0 as well for 0th and 2nd order reactions)
First order equation is on reference table

46
Q

Reaction mechanism

A

Series of steps in a chemical reaction

Kinetics helps to elucidate a reaction mechanism.

47
Q

Intermediate

A

Species generated and consumed during a reaction.

48
Q

Elementary sep

A

A reaction whose rate law can be determined from its moleculaity, the number of species that must collide to produce the reaction indicated in the elementary step. The coefficient is the order in a given elementary step
Note: rate cannot be in terms of an intermediate. Needs to be a real reactant.

49
Q

Rate determining step

A

Slowest step in a reaction, the rate is dependent on it. The rate of the overall reaction = rate of the RDS

50
Q

Requirements for a reaction mechanism to be applicable

A
  1. The sum of the elementary steps must give the overall balanced equation for the rxn
  2. The mechanism must agree with the experimentally determined rate law.
51
Q

What is rate dependent on?

A
  1. Concentration of material for non-zeroth order –> increase concentration, rate increases
  2. Temperature–> more molecules with high enough Energy
  3. Collisions with higher energy
  4. Orientation of molecules – overcome activation energy
52
Q

How does temperature influence rate of a reaction?

A

Higher temperature speeds up a reaction
Think about boiling at sea level vs altitude. At altitude, Lower pressure in the atm, so boiling point less, and thus it takes longer to boil because less energy in the system.
More collisions at higher temperature

53
Q

Collision model

A

A model used to account for the observed characteristics of reaction rates.
Model is built around the central idea that molecules must collide to react.
Found that only a small fraction of the collisions produces a reaction. This because of a threshold energy, the activation energy, that must be overcome for a reaction to occur.
Energy to break the bonds comes from kinetic energies possesses by reacting molecules before the collision. Kinetic energy changed to potential energy as molecules are distorted during collision to break bonds and rearrange the atoms into the product molecules.

54
Q

Activation energy

A

Energy that must be overcome to produce a chemical reaction.

55
Q

Molecular orientation

A

Important in determining reaction rates
Observed reaction rate is considerably smaller than raye of collisions with enough energy to surmount the barrier. Many collisions, even though they have required energy, still do not produce a reaction. Because of the molecular orientation. While some orientations lead to reaction, others do not. Thus, need a factor in our equation to allow for this.

56
Q

Two requirements for a successful collision

A
  1. Have enough energy, collision energy >= to the activation energy.
  2. Relative orientation of the reactants must allow formation of any new bonds necessary to produce products.
57
Q

Arrhenius equation

A

K, the rate constant, = z * p * e ^ (-Ea/RT)
Z is the collision frequency and p is the steric factor
Ea is activation energy (joules)
R is gas constant (8.31)
T temperature in Kelvin
A = zp
So, k= A * e^ (-Ea/RT)
Ln (k) = -Ea/R (1/T) + ln(A)
Linear relationship of ln (k) vs (1/T) with slope -Ea/R

58
Q

Easier equation for Arrhenius with two different temperatures and K values

A

ln (K2/K1) = (Ea/R) (1/T1 - 1/T2)

59
Q

Catalysts

A

Something added to a reaction to lower the activation energy. Facilitate materials to be oriented correctly
Catalyst not consumed during reaction (amount before = amount after)

Creates a new mechanism with the reaction–> alternate pathway with a lower activation energy than the uncatalyzed reaction

60
Q

Homogenous vs heterogenous catalyst

A

Homogenous –> catalyst and reactant in the same phase (both solids for example)
Heterogenous means they’re in different phases

61
Q

Heterogenous catalysis steps:

A
  1. Adsorption and activation of the reactants.
  2. Migration of adsorbed reactants on the surface
  3. Reaction of adsorbed substances
  4. Escape, or desorption, of the products
62
Q

Adsorption vs absorption

A

Adsorption is the collection of one substance on the surface of another
Absorption is the penetration of one substance into another.

63
Q

How to label energy vs reaction coordinate plot

A

Reactants to peak is activation energy
Reactants to products is delta E
Delta E positive when products have more energy, higher up
Delta E negative when products lower than reactants; products have less energy

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