Chem 30 Formulas



Chemistry 30 – Formulas and Information

Thermochemistry:

|Formula: |Variables: |When to use: |

|Q = mc∆t |Q = total heat/enthalpy (J or kJ) |If given the specific heat capacity, mass and temperature change of one substance.|

| |m = mass (g) | |

| |c = specific heat capacity (J/g◦C or kJ/g◦C) | |

| |∆t = temperature change (◦C) | |

|nH = mc∆t |n = moles of substance reacting (n = cv or m/M) (mol) |Calorimetry questions: |

| |H = molar heat/ enthalpy of substance reacting (J/mol or kJ/mol) |- if given information about a reacting substance and water (remember water is |

| |m = mass of water (1g = 1 mL) |present to determine the energy released or absorbed by the reaction) |

| |c = specific heat capacity of water (J/g◦C or kJ/g◦C) |- usually asked to find the molar enthalpy (H) |

| |∆t = temp. change of water (◦C) | |

|∆H = ∑nfH(products) - ∑nfH(reactants) |∆H = total heat/ enthalpy (J or kJ) |Hess’s Law: |

| |∑nfH (products) = sum of heats of formations of products |- if only have a reaction with no other energy information |

| |∑nfH (reactants) = sum of heats of formations of reactants |- remember: |

| | |- use data booklet for heats of formations of several compounds |

| | |- elements have a heat of formation of zero |

|% efficiency = |% efficiency (%) |If asked for % efficiency and given the energy released and used by a system |

|energy output x 100 |energy output (J or kJ released by a system) | |

|energy input |energy input (J or kJ absorbed by a system) | |

Electrochemistry:

|Formula: |Variables: |When to use: |

|E◦net = E◦red + E◦ox |E◦net = net voltage of a cell (V) |If asked to find the voltage of a cell: |

| |E◦red = voltage of the reduction half reaction (V) |- the voltages come from the data booklet |

| |E◦ox = voltage of the oxidation half reaction (V) |- 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) |Electrical Stoichiometry: |

| |I = current (C/s or I) |- if given info about an electrolytic process such as running a current and the length of time |

| |t = time (s) | |

|ne = q or It |ne= moles of electrons (mol) |Electrical Stoichiometry: |

|F F |q = charge (C) |- if given info about an electrolytic process such as running a current and the length of time used to |

| |I = current (C/s or I) |produce a solid metal |

| |t = time (s) |- need to write the half reaction of the metal (substance) being electroplated or refined |

| |F = 9.65 x 104 C/mol (Faraday’s Constant) |- use the ne to calculate the n of the reacting substance (multiply n by the |

|n = m or Cv |n = moles of reacting substance (mol) |coefficient ratios wanted/ given) |

|M |m = mass of reacting substance (g) |- use other common chemistry formulas to convert moles back into mass, concentration or volume |

| |M = molar mass of reacting substance (g/mol) | |

| |c = concentration of reacting solution (mol/L) | |

| |v = volume of reacting solution (L) | |

|n = m or Cv |n = moles of reacting substance (mol) |Redox Titrations: |

|M |m = mass of reacting substance (g) |- need to write the net reaction between the SOA and SRA |

| |M = molar mass of reacting substance (g/mol) |- use the ng (of the given substance) to calculate the nw (of the wanted substance) by multiply ng by the|

| |c = concentration of reacting solution (mol/L) |coefficient ratios wanted/ given |

| |v = volume of reacting solution (L) |- 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+] |pH = uses decimal places as SD (no units) |Deals with acids (identified by having H+ ions) |

|[H30+] = [SA] or √(Ka [WA]) |[H30+] = concentration of H+ |SA = strong acids (top 6 in data booklet table) and Ka >1 |

| |[SA] = concentration of strong acid (mol/L) |WA = all other acids (Ka ................
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