module 5 physical chem Flashcards
acid
proton donor
base
proton acceptor
conjugate acid base pairs
HA + OH –> H2O + A
HA & A acid base pair 1
OH- & H2O acid base pair 2
basic equations
acid + metal –> salt + hydrogen
acid + oxide –> salt + water
acid + carbonate –> salt + CO2 + water
acid + hydroxide –> salt + water
pH equation
pH = -log[H+]
[H+] is concentration of H+ atoms
[H+] equation
[H+] = 10-pH
10 to the power of -pH
Diluting pH
X10 everytime to drop down pH
1 –> 2 X10
Ka expression
Ka= [H+] [A-]
[HA]
Ka= [H+]2
[HA]
Ka equation
Ka= 10-PKa
PKa equation
-log(Ka)
working out [H+] conc with Ka
[H+] = Ka x [HA]
Kw
ionic product of water
1 x 10-14
working out [H+] in alkali
you are given OH conc (overall conc)
[H+] = 1 X 10-14 / [OH-]
then put into pH equation (-log[H+] )
working out [H+] in alkali
method 1
you are given OH conc (overall conc)
[H+] = 1 X 10-14 / [OH-]
then put into pH equation (-log[H+] )
working out [H+] in alkali
method 2
you are given OH conc
put into equation POH = -log[OH-]
then do 14 - POH = pH
Rate of reaction definition
change in conc of reactant or a product per unit time
Ways to measure rate of chemical reaction
Volume of gas production
Measure loss in mass
Measure increase in mass
Measure colour change
Zero order reaction (conc&rate)
changing the concentration of the reactant has NO affect on rate of reaction
(straight horizontal line on graph)
First order reaction (conc&rate)
Rate of reaction is directly proportional to the conc of the product
-doubling conc doubles rate
1:1
Straight diagonal line through origin
Second order reaction (conc&rate)
Rate of reaction will equal concentration squared
2:1
Curved horizontal line up
Rate constant K
Rate = K [A][B][C]
constant that links the rate of reaction with conc
concentration has powers depending on order
Overall order
All orders added together
Indices
Zero order (conc&time)
Half life decreases over time
straight diagonal line downwards on graph
first order (conc&time)
Half life is constant over time
Downwards curve on graph
Second order (conc&time)
Half life increases over time
Steep downwards curve on graph
Calculating rate constant from half life
K = ln2 / t 1/2
Clock reaction
Chemical reaction where one of the chemical products initially has a low conc but gradually increases with time
-amount of time it takes for mixture to change colour
Rate determining step
The slowest step in the reaction mechanism of a multistep reaction
step with largest activation energy
Creating a multi step reaction
compounds in the rate equation must be in the first step of the multi step reaction
Maxwell boltzman curve
higher temp = higher proportion of molecules with activation energy
Arrhenius equation
K = Ae to the power of -Ea/RT
e = 2.718
A = pre exponential factor
R = gas constant 8.312
T = temp (kelvin)
Ea = activation energy
Rearranged arrhenius equation
K = -Ea/R x 1/T + lnA
Arrhenius equation with graph
Y = M X + C
lnk = -Ea/R 1/T + lnA
Kc
used to calc the exact position of equilibrium
1 equal lies halfway
greater than 1 equilibrium lies to right
less than 1 equilibrium lies to left
Kc = [products]
[reactants]
Practical techniques used to study equilibrium
-Colorimetry
-Titration
homogenous
where all reactants and products are in the same state eg all (g)
heterogenous
where products and reactants are in different states
Kc equations don’t include solid and liquid states
