Chem 30 Formulas - 123 PDF

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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: Variables: ◦ ◦ ◦ E = net voltage of a cell (V) E net = E red + E ox E = voltage of the reduction half reaction (V) ◦ net ◦ red ◦ ox

E

q = It ne = q or It F F

= voltage of the oxidation half reaction (V)

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)

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 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)

n = m or Cv M n = m or Cv M

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)

- use other common chemistry formulas to convert moles back into mass, 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 Ka >1 WA = all other acids (Ka...