Thermo Unit:
Formula:
Q = mc∆t
Q = C∆t
∆H = nH
nH = mc∆t
m1H = m2c∆t
Variables:
Q = total heat/ enthalpy (J or kJ)
m = mass (g)
c = specific heat capacity (J/g◦C or kJ/g◦C)
∆t = temp. change (◦C)
Q = total heat/ enthalpy (J or kJ)
C = heat capactity (J/◦C or kJ/◦C)
∆t = temp. change (◦C)
∆H = total heat/ enthalpy (J or kJ)
n = moles (n = cv or m/M) (mol)
H = molar heat/ enthalpy (J/mol or kJ/mol)
n = moles of substance reacting (n = cv or m/M) (mol)
H = molar heat/ enthalpy of substance reacting (J/mol or kJ/mol)
m = mass of water (1g = 1 mL)
c = specific heat capacity of water (J/g◦C or kJ/g◦C)
∆t = temp. change of water (◦C)
m1 = mass of substance reacting (g)
H = molar heat/ enthalpy of substance reacting (J/g or kJ/g)
m2 = mass of water (1g = 1 mL)
c = specific heat capacity of water (J/g◦C or kJ/g◦C)
∆t = temp. change of water (◦C)
∆H = sum of rxns
∆H = total heat/ enthalpy (J or kJ)
Note: different forms of H indicate the type of reaction:
fH = formation reaction
cH = combustion reaction
neutH = neutralization reaction
∆H = ∑nfH(prod.) - ∑nfH(react.)
∆H = total heat/ enthalpy (J or kJ)
∑nfH(prod.) = sum of heats of formations of products
∑nfH(react.) = sum of heats of formations of reactants
% efficiency = energy output x 100
energy input
% efficiency (%)
energy output (J or kJ given off or released by a system)
energy input (J or kJ used or absorbed by a system)
When to use:
If given the specific heat capacity, mass and temp. change of one
substance.
If given the heat capacity, and temp. change of one substance.
If given the molar enthalpy and the amount of one substance
Note: + values mean endothermic
- values mean exothermic
Calorimetry questions:
- if given information about a reacting substance and water
(remember water is present to determine the energy released or
absorbed by the reaction)
- usually asked to find the molar enthalpy (H)
Calorimetry questions:
- if given information about a reacting substance and water
(remember water is present to determine the energy released or
absorbed by the reaction)
- usually asked to find the enthalpy per gram (H)
- usually given mass of something with an unknown molar mass
Hess’s Law of Additivity:
- if given several reactions you can manipulate them to add up
and get the overall reaction energy
- remember:
- if you flip a reaction ∆H also flips (ie. + to -)
- if you multiply a reaction, multiply ∆H also
Hess’s Law:
- if only have a reaction with no other energy information
- remember:
- use data booklet for heats of formations of several compounds
- elements have a heat of formation of zero
If asked for %efficiency and given the energy given off and used
by a system
Electro Unit:
Formula:
E◦net = E◦red + E◦ox
Variables:
E◦net = net voltage of a cell (V)
E◦red = voltage of the reduction half reaction (V)
E◦ox = voltage of the oxidation half reaction (V)
q = It
q = charge (C)
I = current (C/s or I)
t = time (s)
ne= moles of electrons (mol)
q = charge (C)
I = current (C/s or I)
t = time (s)
F = 9.65 x 104 C/mol
n = moles of reacting substance (mol)
m = mass of reacting substance (g)
M = molar mass of reacting substance (g/ mol)
c = concentration of reacting solution (mol/ L)
v = volume of reacting solution (L)
n = moles of reacting substance (mol)
m = mass of reacting substance (g)
M = molar mass of reacting substance (g/ mol)
c = concentration of reacting solution (mol/ L)
v = volume of reacting solution (L)
ne = q
F
or It
F
n=m
M
or cv
n=m
M
or cv
When to use:
If asked to find the voltage of a cell:
- the voltages come from the data booklet
- the oxidation half reaction comes from flipping the reduction half reaction in the
data booklet (remember to flip the voltage sign as well, but you don’t need to multiply
the voltage if reaction was multiplied for equal electron transfers)
Electrical Stoich:
- if given info about an electrolytic process such as running a current and the length
of time
Electrical Stoich:
- if given info about an electrolytic process such as running a current and the length
of time used to produce a solid metal
- need to write the half reaction of the metal (substance) being electroplated or refined
- use the ne to calculate the n of the reacting substance (multiply n by the
coefficient ratios wanted/ given)
- use other common chemistry formulas to convert moles back into mass,
concentration or volume
Redox Titrations:
- need to write the net reaction between the SOA and SRA
- use the ng (of the given substance) to calculate the nw (of the wanted substance) by
multiply ng by the coefficient ratios wanted/ given
- use other common chemistry formulas to convert moles back into mass,
concentration or volume
EAB Unit:
Formula:
pH = -log [H30+]
[H30+] = [SA] or √(Ka [WA])
Ka = [H30+]2
[acid]
pOH = -log [OH-]
[OH-] = x [SB] or √(Kb [WB])
Kb = [OH-]2
[base]
or Kw
Ka
pH = 14 – pOH
[H30+] = 10-pH
[OH-] = 10-pOH
% ionization = [H30+] x 100
[acid]
Variables:
pH = uses decimal places as SD (no units)
[H30+] = concentration of H+
[SA] = concentration of strong acid (mol/L)
[WA] = concentration of weak acid (mol/L)
Ka = ionization constant of an acid (no units)
(in data booklet)
pOH = uses decimal places as SD (no units)
[OH-] = concentration of OHx = number of OH[SB] = concentration of strong base (mol/L)
[WB] = concentration of weak base (mol/L)
Kb = ionization constant of a base (no units)
(NOT in data booklet)
Kw = 1.0 x 10-14
Review formulas from Chem 20
When to use:
Deals with acids (identified by having H+ ions)
SA = strong acids (top 6 in data booklet table) and K a >1
WA = all other acids (Ka <1)
% ionization of an acid (%)
If asked how well an acid ionizes in water
- strong acids are 100%
- weak acids are <100%
Deals with bases (identified having a negative ion charge - also NH3)
SB = strong bases (have OH-)
WB = weak bases (all other elements/ molecules with a negative ion charge)
If asked for ion concentrations and have the pH or pOH of that substance