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## Useful Chemistry Equations

 % ERROR = Measurement (or average measurement) – Correct (accurate) measurement                  _____________________________________________________________          x 100  Correct (accurate)

 DENSITY = Mass (g or kg) ______  Volume (cm3 or m3- solids and ml or l – liquids)

 PERCENTAGE COMPOSITION = Mass of part                       ______          x100       Mass of whole

 MOLARITY = MOLS of solute ______  Liters of solution

 MOLALITY = MOLS of solute ______  Mass of solvent in KG

 RATE OF REACTION = Difference in quantity ______  Difference in time

 MOLS = Mass in grams ______  Relative formula mass (atomic mass)

 RELATIVE FORMULA MASS (ATOMIC MASS)= (Number of atom 1 )(Mass of atom 1) + (Number of atom 2)(Mass of atom 2) + …..

 CONCENTRATION = Number of moles ______  Volume in liters

 NUMBER OF MOLECULES= Moles of substance X Avogadro’s number

 Wavelength of light emitted from Atom= Energy of photon (j) = Change in Energy= -Rh (1/n(final) squared – 1/n(initial) squared) Rh = 2.179*10-18 Wavelength of light emitted = hc/Energy of photon h = 6.626*10-34 j.s c = 3*10+8 m/s

 SOLUBILITY PRODUCT= [PRODUCT 1]^m[PRODUCT]^n (n and m are the coefficients in the balanced equation of the salt dissolving)

 Speed of Gas = 3RT/M R = 8.31447 J/mol K and M = Molar Mass of molecules and T = Temperature in Kelvin. Answer is in m/s. Rate of GAS A/Rate of GAS B= Molar Mass of Gas B/Molar Mass of Gas A

 IDEAL GAS relationship P.V = n.R.T P = Pressure in either atm or pa. V – volume in liters. n = mols. R = 0.082 (for atm) and 8.314 (for pa). T = Temperature in Kelvin.

 GRAMS TO MOLS (divide by Molar Mass). TO GRAMS (multiply by Molar Mass) MOLS TO MOLECULES (multiply by 6.022×10*23). TO MOLS (divide by 6.022×10*23) MOLECULES

 LIMITING REACTANT To calculate the limiting reactant we need to see which molecule is in excess, the other molecule will be the limiting reactant. To do this we calculate the moles of both reactants and compare them to the balanced equation to see which one will be in excess. For all the moles of molecule A to be used up, how many moles of molecule B do we need? MOLES of molecule A x coefficient of B/coefficient of A = Moles of B to use all of A

 THEORETICAL AND ACTUAL YIELD Theoretical yield is the yield in (grams, moles, etc.) that we calculate using formulas. This is the most (maximum) that could be produced. Actual yield is the yield in (grams, moles, etc.) that is really produced.

 HEAT OF A REACTION To calculate the heat of a reaction using bong energies use this: (SUM of bond energies of the bonds broken) – (SUM of bond energies of the bonds formed)

 TYPE OF BOND To calculate the type of bond use this: electronegativity value of ATOM A – electronegativity value of ATOM  B If the answer is between 0 and 0.3 it is a non polar covalent bond. If the answer is between 0.3 and 1.7 it is a polar covalent bond. If the answers is between 1.7 and 3.5 it is an ionic bond. Any values that is on the borders can be either, or something in between (remember science is an approximation).

 EQUILIBRIUM K = [PRODUCT A]^coefficient in balanced equation [PRODUCT B]^coefficient in balanced equation/[REACTANT A]^coefficient in balanced equation[REACTANT B]^coefficient in balanced equation When K is bigger then 1 we say that the products are favored. When K is around 1 we say that neither one side is favored. When K is less then 1 we say that the reactant side is favored.