Yield and atom economy

Question 1

Yield

Answer 1

The mass of product produced from a reaction
Could be theoretical, actual or as a percentage

Question 2

Actual yield

Answer 2

the weighted mass/ moles of product that was produced in the reaction

Question 3

Theoretical yield

Answer 3

The maximum mass of a product that can be made with a given mass of reactant

Question 4

How to calculate theoretical yield?

Answer 4

By calculating the mass of the product using moles and the Mr of reactants

Question 5

What conditions must be met to achieve theoretical yield?

Answer 5

The reaction goes to completion (all reactants react)
No side reactions occur
No products lost during filtration

Question 6

Actual yield

Answer 6

Actual mass of product formed
Obtained by measuring rather than by calculation

Question 7

Percentage yield

Answer 7

Shows how much product is obtained relative to the maximum theoretical mass
Displayed as a percentage

Question 8

How to find percentage yield?

Answer 8

Actual yield
—————— x100
Theoretical yield

Question 9

How to calc percentage yield when given the equation and actual yield only?

Answer 9

Determine the theoretical yield using moles and molar ratio
Put numbers into equation to calculate the percentage yield

Question 10

What to remember when calculating the percentage yield?

Answer 10

Sometimes yields are given as moles or as masses, it’s the same process to find % mass but make sure both values are in the same unit (also in terms of kg or g etc)

Question 11

Why might the actual yield not be the same as theoretical yield (or rather, why is the % yield not 100%?)

Answer 11

The reaction = reversible so may not be complete
There are side-reactions that lead to other unwanted products
Product may need to be purified, which may result in loss of product eg by filtration

Question 12

Why do we want a higher % yield?

Answer 12

You want to obtain as much product from the reactants you were given
In manufacturing, for economic reasons to gain more product and reduce production costs

Question 13

Atom economy

Answer 13

The molar mass of the desired product divided by the total molar masses of all products in a reaction
Expressed as a percentage

Question 14

How to calculate the atom economy of a reaction?

Answer 14

Mr of desired product
——————————— x 100
Mr of all products

Question 15

Why do we want to consider the atom economy in a reaction?

Answer 15

Because even if the percentage yield is high, we need to consider how many atoms of the reactants actually make the product we want in order to reduce industry costs

Question 16

If the atom economy is low, what might justify using the process anyway?

Answer 16

If the other products can be sold anyway so won’t be too costly economic wise