HIGHER GRADE CHEMISTRY CALCULATIONS
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HIGHER GRADE CHEMISTRY CALCULATIONS
Calculation of percentage yield.
Percentage yield is calculated using the formula:-
percentage yield = x 100
The actual yield is given in the question. The theoretical yield is calculated from the balanced equation.
actual yieldtheoretical yield
Worked example.
In a reaction 320 kg of sulphur dioxide reacted with oxygen to form 360kg of sulphur trioxide. Calculate the percentage yield.
Find the theoretical yield using the balanced equation:-
2SO2 + O2 2SO3
2 mol 2 mol
128.2 g 160.2 g
128.2 kg 160.2 kg
320 kg 399.9 kg
percentage yield = x 100 = 90.0%
360
399.9
Higher Grade Chemistry
Calculation of percentage yield.
Calculations for you to try.
1. 0.5 tonnes of hydrogen reacts with excess nitrogen to form
0.66 tonnes of ammonia.
N2 + 3H2 2NH3
Calculate the percentage yield of ammonia.
N2 + 3H2 2NH3
3 mol 2 mol
6 g 34 g
6 tonnes 34 tonnes
0.5 tonnes 2.83 tonnes
percentage yield = x 100 = 23.32%
0.66
2.83
Higher Grade Chemistry
Calculation of percentage yield.
Calculations for you to try.
2. Ethene reacts with steam to ethanol
C2H4 + H2O C2H5OH
Calculate the percentage yield of ethanol when 140g of
ethene reacts to form 170 g of ethanol.
C2H4 + H2O C2H5OH
1 mol 1 mol
28 g 46 g
140 g 140/28 x 46 g
230 g
percentage yield = x 100 = 73.9%
170
230