Amount of Substance

Equations used in chem unit 1.


Number of moles, mass and Mr.

n = M / Mr 

Number of moles = mass of substance / molecular mass of substance.

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Solution Calculations

n = CV/1000

Number of moles = (concerntration * volume) / 1000

Conc. in mol per dm^3

Vol. in cm^3

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Ideal Gas Equation

PV = nRT

Pressure * Volume = Number of moles * Gas constant * Temperature

Press. in Pa

Vol. in M^3

Gas con. 8.31JK^-1mol^-1

Temp. in kelvin (temp in °C add 273)

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Atom Economy and % Yield

The atom economy of a chemical reaction is a measure of the amount of starting materials that become useful products.

% atom economy = (Mass of desired product / Total mass of reactants) * 100

In practice, it is not always possible to get the calculated amount of product in a reaction:

  • reversible reactions may not go to completion
  • some product may be lost when it is removed from the reaction mixture
  • some of the reactants may react in an unexpected way

The yield of a reaction is the actual mass of product obtained.

% Yield = (Actual mass of product / theoretical mass of product) * 100

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