chem 2 exam

Solution

homogenous mixtures where a solute is dispersed throughout a solvent

more moles

lower molar mass

when you see % by mass choose

100 g of solution and use mass percent to get mass of solute

how to calc molar mass

divide g by moles

solute

dissolves

if nonelectrolyte, i equals

1

solvent

does the dissolving

How do we express concentrations in solutions qualitatively

dilute, concentrated

How do we express concentrations in solutions quantitatively

mass percentage/ppm/ppb

mole fraction

molarity and molality compare

solute to the whole using different units

mass percent ex

5% nacl

if we had 100 g of solution, 5g would be NaCl and 95 g would be water

Mass percent equation

(mass of solute/total mass of solution) x 100

unitless

density of water at room temp

1g/mL

ppm and ppb equations

ppm= (mass of solute/total mass of solution)x 10^6

ppb= (mass of solute/total mass of solution)x 10^9

Mole fraction

x= moles of solute/total moles of solution

max is 1→ pure substance

molarity

depends on temp bc volume changes with temp

M=moles of solute/L of solution

molality

does not depend on temp bc the mass of the solution will no change with temp

m=moles of solute/kg of solvent

1 kg

1×10³

Colligative Properties

physical properties of solutions that depend on the quantity of solute particles present

they do NOT depend on the identity of the particles

what are the four Colligative Properties

osmotic pressure

vapor pressure lowering

boiling pt elevation

freezing pt depression

osmosis

net movement of a solvent from an area of low solute concentration to an area of high solute concentration

solvent moves through a semipermeable membrane

solute cannot pass through membrane

semipermeable

solvent can cross the membrane but solute cannot

osmosis is from

low to high concentration

osmotic pressure (pi)

the pressure needed to stop the movement of solvent throught the membrane

force generated from osmosis

osmotic pressure equation

v= volume (L)

n= moles

R= ideal gas constant→ 0.0821

T=temp (K)

M=molarity

ex of osmotic pressure

salt concentration of blood cells

when the solution concentrations on both sides of the membrane are equal they are

isotonic

when the concentrations are unequal, the more concentrated solution is ___ and the less concentrated solution is ___

hypertonic

hypotonic

reverse osmosis

used to remove contaminants from solutions

similar to filtration

applied pressure forces the solution through a membrane permeable to water, but not permeable to dissolved components

van’t Hoff Factor

i=moles of particles in solution/moles of fu dissolved

osmotic pressure equation using van’t hoff factor

pi=iMRT

vapor pressure

pressure exerted by vapor above a liquid in a closed container

explain this

from left-right: stronger IMGS

boil at lower temp if pressure is lower

equation:

The vapor pressure of a solution containing a nonvolatile solute is ___ than the vapor pressure of the pure solvent

lower

the solute-solvent interaction make is difficult for the

solvent particles to escape into the vapor

raoult’s law

phase diagram for a solution

The graph shows how adding a nonvolatile solute changes the phase behavior of a solvent.

The solute lowers vapor pressure, which causes the solution to have a lower freezing point and a higher boiling point than the pure solvent.

These effects are called colligative properties because they depend on the number of dissolved particle

the boiling pt of a solution is

higher than that of a pure liquid

boiling pt eleavation formula

m=molality

the freezing point of a solution is

lower than that of the pure liquid

freezing pt depression equation

Solubility of gases generally

decreases as the temp increases

solubility depends on

IMFs and thermodynamic properties of the solvation process

Henrys Law

C= solubility

K is henrys law constant

P is the partial pressure

solubility is directly proportional to

the pressure of a gas over the solution

strong electrolytes

soluble ionic compounds, strong acids, strong bases

weak electrolytes

weak acids, weak bases, slightly soluble ionics and very few covalents

nonelectrolytes

organic compounds and most covalents

strong acids

HCl, HBr, HI, HClO4, H2SO4, HNO3

strong bases

group 1 hydroxides, Ca(OH)2, Ba(OH)2, Strontium hydroxide

weak acids

HC2H3O2, HF, HClO, HNO2, H2CO3, H3PO4, H2S

Photochemical smog

a mixture of gases formed when sunlight interacts with compounds produced in internal combustion engines

the speed and timescale of reactions can be studied by

chemical kinetics

kinetics

the rate at which chemical reactions occur

we can use kinetics to understand

the rate at which reactions occur

the factors that influence reaction rate

the reaction mechanism, or exactly how the reaction occurs

Rate of reaction

proportional to the rate of reactant collisions: rate collisions/time

collision theory

the reacting species must collide in an orientation that allows contact between the atoms that will become bonded together in the product (steric factor)

the collision must occur with adequate energy so that atoms can rearrange and form new bonds (and new chemical species)

Collision theory conditions

molecules must collide

molecules must collide in the proper orientation

molecules must collide with sufficient energy

reaction rate

how rapidly a reaction occurs, usually expressed as concentration/time (M/s)

Factors affecting reaction rates

physical states of the reactants → # collisions, energy

concentration of reactants → # collisions (more stuff, more likely things are to collide)

temperature → # collisions, energy (more temp, more energy)

surface area→ # collisions, orientation (bigger the molecule, the morelikely it is to running into something)

catalysts → orientation, energy

rates of reactions can be determined by

monitoring the change in concentration of either reactants or products as a function of time

rate=

change in concentration/change in time

rate of disappearance

reactants

negative

rate of appearance

products

positive

in general for a reaction:

three types of reaction rates

average rate

instantaneous rate

initial rate

average rate

calculated by subtracting an initial concentration and time from any subsequent concentration and time

instantaneous rate

the rate at any given pt in time

corresponds to the slope a line tangent to the concentration v. time

would have to draw the tangent line and calculate the slope

initial rate

the instantaneous rate at t=0

a general rate law can be written

k[A]^m[B]ⁿ

describes the rate of reaction as a function of concentration of teh reactants

k

rate constant

m and n

the reaction order

the overall order is the

sum of the exponents

when the concentration doubles

the initial rate doubles

we can gain information about the rate of reaction by

seeing how the rate changes in inital concetrations of reactants

integrated rated laws

provide a way to determine concentration as a function of time

zero order equation

first order equation

second order equation

when calculating exponents for a rate

choose the reactions where one of the rates cancels

always put the bigger rate on top

to calculate total mols/mass of solution

add the mols/g of solute and solvent together

for first order reactions, no matter what the astarting concentration is

it will take the same amount of time to reach the desired concentration

Half life

the time required for one-half of a reactant to react

Half life zero order

half life first order

half life second order

slope=

y2-y1/x2-x1= -k

transition state

a proposed high-energy transient state between products and reactants

acitvated complex

specific chemical species in the transition state

what is always soluble

acids, ammonia, Na, K, NH4, nitrates, and acetates

all chlorides are soluble except

AgCl, HgCl2 and PbCl2

all bromides are soluble except

AgBr, PbBr2, HgBr2

all iodides are soluble except

AgI, PbI2, HgI2

All sulfates are soluble except

PbSO4, HgSO4, SrSO4, BaSO4, Ag2SO4, CaSO4

all sulfides are insoluble except for

Group 1, 2 and ammonium

all hydroxides are insoluble except

group 1, ammonium, ba, sr, and ca

all carbonates, phosphates, and sulfites are insoluble except

group 1 and ammonium

reaction profile

allows use to visualize the energetics and progress of a reaction

exothermic reaction profile

Ea→ activation energy

delta H: difference in energy between products and reactants; negative

endothermic reaction profile