The Yield of a Reaction

Question 1

what are the three reasons why the mass of a reaction product may be less than the maximum to be possibly obtained

Answer 1

• the reaction may be reversible and so may not be complete
• there are side reactions that lead to unwanted products
• the product may need to be purified which leads to a loss of product

Question 2

what are the three main factors that the yield of a reaction of a reaction is referring to

Answer 2

• theoretical yield
• actual yield
• percentage yield

Question 3

what is the difference between how yield is measured in labs and in industry

Answer 3

• in labs, grams would be used as smaller portions are being used
• but in industry, kilograms or tonnes would be used
• as they are reacting substances in very large quantities

Question 4

how do you calculate theoretical yield

Answer 4

• using the equation
• you calculate the mass of the desired product using some maths
• assuming there is no loss and the reaction is complete

Question 5

magnesium phosphate is prepared in the reaction 3Mg + 2H3PO4 = Mg3(PO4)2 + 3H2. what is the theoratical yield of magnesium phosphate obtainable from 5.62g of magnesium, given that the Mr of 3Mg = 72 and Mg3(PO4)2 = 262

Answer 5

• you need to find the moles of 3Mg youre working with
• Mr of 3Mg = 72gmol-1
• moles = mass /Mr
• so 5.62 / 72 = 0.078 mols
• Mr of the other one = 262g
• so 262 x 0.078 = 20.4g

Question 6

this reaction is used to obtain methanol from carbon monoxide and hydrogen: CO + 2H2 = CH3OH. given that he obtains 4.07 tonnes of methanol starting from 4.32 tonnes of CO, what is the percentage yield

Answer 6

• ideally you should convert the tonnes into grams but cba
• Mr of CO = 28g
• moles = mass / Mr
• 4.32 / 28 = 0.154 mols
• Mr of CH3OH = 32g
• 32 x 0.154 = 4.982g
• (4.07 / 4.982) x 100 = 82.4%