Download Chem 30 Formulas

Chemistry 30 – Formulas and Information
Thermochemistry:
Formula:
Q = mc∆t
nH = mc∆t
∆H = ∑nfH(products)
- ∑nfH(reactants)
% efficiency =
energy output x 100
energy input
Variables:
When to use:
Q = total heat/enthalpy (J or kJ)
m = mass (g)
c = specific heat capacity (J/g◦C or kJ/g◦C)
∆t = temperature change (◦C)
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)
∆H = total heat/ enthalpy (J or kJ)
∑nfH (products) = sum of heats of formations of products
∑nfH (reactants) = sum of heats of formations of reactants
If given the specific heat capacity, mass and temperature change
of one substance.
% efficiency (%)
energy output (J or kJ released by a system)
energy input (J or kJ absorbed by a system)
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)
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 released and used
by a system
Electrochemistry:
Formula:
E◦net = E◦red +
E◦ox
Variables:
When to use:
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 (Faraday’s Constant)
n = moles of reacting substance (mol)
m = mass of reacting substance (g)
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 Stoichiometry:
- if given info about an electrolytic process such as running a current and the length
of time
Electrical Stoichiometry:
- 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,
ne = q or It
F
F
n = m or Cv
M
n = m or Cv
M
M = molar mass of reacting substance (g/mol)
c = concentration of reacting solution (mol/L)
v = volume of reacting solution (L)
concentration or volume
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)
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
Equilibrium of Acids & Bases 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 or Kw
[base]
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)
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)
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
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)
Review formulas from Chem 20
If asked for ion concentrations and have the pH or pOH of that substance
% ionization of an acid (%)
If asked how well an acid ionizes in water
- strong acids are 100%
- weak acids are <100%