Chem 205 Exam I

add/subtract

lest amount of digits past the decimal

mult/divide

least number of sigfigs

exponents

only numbers past the decimal are significant

last digit is uncertain by 1

basic assumption of sigfigs

homogenous mixtures

evenly spread out

solutions

particles molecule sized (clear)

colloids

particles are larger ex: milk or smoke clouds

gas gas

air

gas liquid

pop/soda

gas solid

H2 in Pd

liquid liquid

H2O and ethanol

liquid solid

Hg in Ag

solid liquid

NaCl(aq)

solid solid

alloys like bronze

like dissolves like

if the IMFs between solvent molecules are similar to IMFs between solute molecules solute is soluble in solvent

enthalpy change at constant pressure

∆H

endo/need energy

∆H>0

exo/gives off

∆H<0

∆solnH

∆Hsolvent-solvent + ∆Hsolute-solute + ∆Hsolute-solvent =

separating solvent molecules

∆Hsolvent-solvent>0 energy is needed to break IMFs

separating solute molecules

∆Hsolute-solute>0 energy is needed to break IMFs

combine solute and solvent molecules

∆Hsolute-solvent<0 energy is given off as they form IM attractions

temp will decrease

if ∆solnH is positive (∆H>0)

temp will increase

if ∆solnH is negative (∆H<0)

molarity

C_B = n_B/V (mol/L)

mole fraction

x_B = n_B/n (none)

mass percent

p_B = 100m_B/m (%)

molality

b_B = n_B/m_A (mol/kg)

colligative properties

properties that depend on the amount of solute dissolved not its identity

4 colligative properties

raoults law, freezing point depression, boiling point elevation, and osmosis

miscible

solute and solvent will mix in any proportion

temperature and pressure

if not miscible amount of solute that dissolves depends on

more soluble

in general solids in liquids at higher T

less soluble

gasses in liquids at higher T

no affect

pressure on solubility of liquids and solids

large effect

pressure on solubility of gasses

saturated

maximum amount of solute has dissolved in solution

henrys law

the solubility of a gas in a liquid at a given temp is directly proportional to the partial pressure of the gas over the solution

henrys law equation

c_B = kp_B

pressure increase

gas particles forced in solution > gas particle leaving solution so gas solubility increases until equilibrium is reached

nonvolatile solute

has no vapor pressure of its own

volatile solute

has significant vapor pressure of its own

if solute is volatile

the vapor pressure of mixture is intermediate between vapor pressure of 2 pure liquids

if solute is nonvolatile

the vapor pressure of solution is ALWAYS lower than that of pure solvent

raoults law for nonvolatile solute +

p_A = x_Ap*_A

raoults law for volatile solute

p = x_Ap*_A + x_Bp*_B

ideal solution

a solution that obeys raoults law and IMFs between solute molecules = IMFs between solvent molecules

more dilute

all solutions get more ideal as solutions get

i

vant hoff factor = moles of particle in solution/moles of solute added

vant hoff factor is

actual extent of dissociation since ionic substance rarely dissociate completely

boiling point

∆T_b = k_bb_Bi

freezing point

∆T_f = -k_fb_Bi

osmotic pressure

∏ = ic_BRT

reverse osmosis

influx of pressure>∏ causing high conc water to move to lower conc water (seawater→pure water)

rate

-1/a ∆[A]/∆t = -1/b ∆[B]/∆t = 1/c ∆[C]/∆t = 1/d ∆[D]/∆t

reaction rate

change in concentration(molarity)/change in time

positive

reaction rates must be

why negative A and B

A/B are reactants so ∆[A] will be negative

why 1/a

to keep rates equal when some are used up more than other

slow down

as time goes on reaction rates

less reactant left to react

why do reaction rates slow down as time goes on?

average rate

involves finite concentrations/finite time

instantaneous rate

rate at a specific point in time