Yield and atom economy (3.3)

Question 1

3 reasons

Why is it not always possible to obtain the calculated amount of a product?

Answer 1

• the reaction may not go to completion because it is reversible (completion impossible in reversible reaction)
• some of the product may be lost when it is separated from the reaction mixture
• some of the reactants may react in ways different to the expected reaction.

also gas product may be formed, which escapes into the atmosphere

Question 2

What is the yield?

Answer 2

the amount of a product obtained

Question 3

What is the formula for the percentage yield?

Answer 3

% yield = mass of product actually made / maximum theoretical mass of product x 100

when we calculate mass in balanced equation, we calculate theoretical mass, not actual

Question 4

What is the atom economy (atom utilisation)?

Answer 4

a measure of the amount of starting materials that end up as useful products

Question 5

2 reasons

Why is important to use reactions with a high atom economy?

Answer 5

• for sustainable development
• for economic reasons

Question 6

What is the formula for atom economy?

Answer 6

atom economy = relative formula mass of desired products / sum of relative formula mass of all reactants x 100

Question 7

In most cases, the reaction pathway chosen will be the one with the (…) atom economy

Answer 7

greater/highest

may also be based on the yield, rate, equilibrium position and usefulness of by-products

Question 8

5 things

What are some factors that could affect which reaction pathway is chosen?

Answer 8

• atom economy
• the yield
• rate
• equilibrium position
• usefulness of by-products

probably not mandatory to know all, just get a general idea and set to level 5