Lesson 3: Limiting reactants/ Percentage Yield atom economy

Question 1

If there is a limiting quantity of reactant, how does that effect the product that is made?

Answer 1

• Less moles/ mass of the product would be made.

Question 2

Why do we use an excess of one reactant in a chemical reaction?

Answer 2

• To ensure all of the other reactant is used up.

Question 3

What is the reactant that is fully used up in a reaction called and why?

Answer 3

• The Limiting Reactant because it “limits” the amount of product that can be made.

Question 4

Give 3 reasons as to why it’s not always possible to obtain the calculated amount of product, even though atoms aren’t gained/ lost in a chemical reaction.

Answer 4

1.) The reaction may not go to completion because it is reversible.
2.) Some of product may be lost when it is separated from the reaction mixture.
3.) Some reactants may react in different ways to the expected reaction.

Question 5

What is the amount of product obtained known as?

Answer 5

• The amount of product obtained is known as the yield.

Question 6

What is percentange yield?

Answer 6

• The amount of product made compared with the theoretical amount that could be made.

Question 7

What is atom economy (atom utilisation?)

Answer 7

• Atom economy is a measure of how many starting atoms (materials) end up as useful products.

Question 8

Why is it useful to for reactions to have a high atom economy?

Answer 8

1.) By mimising the production of unwanted products, we save money.
2.)Increased sustainability by not wasting resources

Question 9

How might chemists deal with unwanted products?

Answer 9

• Unwanted products are a waste of money
• Chemists try to find uses for these by- products eg. in other reactions.
• That way, money is not wasted.