Percentage/atom economy

Question 1

%yield =

Answer 1

actual amount,in mol, of product / theoretical amount,in mol, of product x 100

Question 2

Give some reasons why yields of 100% are rarely obtained.

Answer 2

• reaction may be at equilibrium and may not go to completion.
• side reactions leading to by-products
• reactants not pure
• reactants/products left behind in apparatus.
• separation may lead to loss of product.

Question 3

atom economy=

Answer 3

molecular mass of the desired product / sum of molecular masses of all products x 100

Question 4

Define a limiting reagent.

Answer 4

A limiting reagent is the substance in a chemical reaction that runs out first.

Question 5

What is done with by-products?

Answer 5

• By-products are often considered as waste and have to be disposed of. This is costly and poses potential environmental problems.
• By-products may be sold or used elsewhere in the chemical plant.