1. 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 yield theoretical 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:- 2SO 2 + O 2  2SO 3 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

2. 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. N 2 + 3H 2  2NH 3 Calculate the percentage yield of ammonia. N 2 + 3H 2  2NH 3 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

3. Higher Grade Chemistry Calculation of percentage yield. Calculations for you to try. 2. Ethene reacts with steam to ethanol C 2 H 4 + H 2 O  C 2 H 5 OH Calculate the percentage yield of ethanol when 140g of ethene reacts to form 170 g of ethanol. C 2 H 4 + H 2 O  C 2 H 5 OH 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