Cheat Sheet for General Chemistry, Cheat Sheet of Chemistry

Download Cheat Sheet for General Chemistry and more Cheat Sheet Chemistry in PDF only on Docsity! Chemistry 30 – Formulas and Information Thermochemistry: Formula: Variables: When to use: Q = mc∆t 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) If given the specific heat capacity, mass and temperature change of one substance. nH = mc∆t 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) 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) ∆H = ∑nfH(products) - ∑nfH(reactants) ∆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 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 % efficiency = energy output x 100 energy input % efficiency (%) energy output (J or kJ released by a system) energy input (J or kJ absorbed by a system) If asked for % efficiency and given the energy released and used by a system Electrochemistry: Formula: Variables: When to use: E◦net = E◦red + E◦ox 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) 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) q = It q = charge (C) I = current (C/s or I) t = time (s) Electrical Stoichiometry: - if given info about an electrolytic process such as running a current and the length of time ne = q or It F F 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) 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 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 = m or Cv M 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: Variables: When to use: pH = -log [H30+] [H30+] = [SA] or √(Ka [WA]) Ka = [H30 + ] 2 [acid] 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) 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 <1) pOH = -log [OH-] [OH-] = x [SB] or √(Kb [WB]) Kb = [OH - ] 2 or Kw [base] Ka pOH = uses decimal places as SD (no units) [OH-] = concentration of OH- x = 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) pH = 14 – pOH [H30+] = 10-pH [OH-] = 10-pOH Review formulas from Chem 20 If asked for ion concentrations and have the pH or pOH of that substance % ionization = [H30 + ] x 100 [acid] % ionization of an acid (%) If asked how well an acid ionizes in water - strong acids are 100% - weak acids are <100%