2. Percentage Yield
A number between 0 and 100 to show how
successful the practical work has been at
producing the desired product.
Equation:
%age Yield = Mass actually produced x 100
Mass expected from
amount of reactant used
3. Example Calculation
CH4 + 2O2 -> CO2 + 2H2O
1. Known Masses 10.0g 19.8g
2. Moles of Moles CH4 = Mass = 10.0 = 0.625 moles
reactant used Mr 16
3. Moles of 1 mole of CH4 makes 2 moles of H2O
Product So 0.625 moles of CH4 makes 1.25 moles H2O
expected (0.625 x 2 = 1.25)
4. Mass of water Mass of H20 = moles x Mr = 1.25 x 18
expected = 22.5g
%age yield = Mass found x 100 = 19.8 x 100 = 88%
5. %age yield
Mass expected 22.5
4. What Can Affect the Yield?
• Transferring the reaction mixture will cause
some product to be lost.
• Spills and splashes will cause some product to
be lost.
• Reaction may not be entirely complete
– Not waiting long enough
– Not mixed properly
– Reaction may not reach 100% complete.
• Product may be wet or contain impurities.
5. Atom Economy
• A number between 0 and 100 that shows how
economically a reaction produces the desired
product.
• The higher the number the more economical
the reaction is.
• No practical work is required to find the atom
economy of a reaction.
6. Equation
% Atom Economy = Mass of desired product from equation x 100
Total mass of products from equation
Since the total mass of reactant is the same as the total mass of
products you can also use:
% Atom Economy = Mass of desired product from equation x 100
Total mass of reactants from equation
7. Example Calculation
C + 2H2O -> CO2 + 2H2
In this reaction the desired product is hydrogen, H2
1. Mr values 12 18 44 2
2. Assume equation number of moles react, so reacting masses are:
1 x 12 = 12g 2 x 18 = 36g 1 x 44 = 44g 2 x 2 =
4g
3. Total mass of Total mass of products = 44 + 4 = 48g
products
A.E. = Product mass x 100 = 4 x 100 = 8.3%
4. Atom Economy
All products 48
