Yield and atom economy

Question 1

How are atoms gained or lost in a reaction

Answer 1

Trick question, they’re not

Question 2

What is a by-product

Answer 2

When reactants form another, non- desired product

Question 3

What is the by-product in the following reaction and why:

CH4(g) + H2O(g) → 3H2(g) + CO(g)

Answer 3

Carbon monoxide because the carbon and oxygen atoms in the reaction don’t form a useful product

Question 4

What is the atom economy of a reaction a measure of

Answer 4

The amount of starting materials that end up as useful products

Question 5

What is the equation for percentage atom economy of a reaction

Answer 5

((Total Mr of desired product)/(total Mr of all reactants)) x 100

Question 6

What does it mean if the atom economy of a reaction is:
A) 50%
B) 100%

Answer 6

A) 1/2 reactants ended up in desired product

B) All reactants ended up in desired product

Question 7

What is the theoretical yield

Answer 7

Highest possible mass of product that can be made in reaction

Question 8

What 3 places can the theoretical yield be calculated from

Answer 8

1) The balanced equation
2) mass/Mr of limiting reactant
3) Mr of product

Question 9

Give 1 of 3 reasons why the mass of product made is less than the maximum theoretical mass

Answer 9

Any 1 of:
. Reaction reversible —> not going to completion
. Product lost when separated from reaction filter
. React differently than expected

Question 10

What is meant by a PERCENTAGE YIELD of:
A) 100%
B) 0%

Answer 10

A) No product lost

B) No product made

Question 11

What is the equation for percentage yield

Answer 11

((Mass of product s actually made)/(maximum theoretical mass of product)) x 100

Question 12

How does one calculate the theoretical yield of magnesium sulphate in:

Mg + H2SO4 —> MgSO4 + H2

When you have 48 grams of Magnesium

(Just work out mass of MgSO4

Answer 12

.Magnesium. .Magnesium sulphate.
Mass/Ar = moles Moles x Mr = mass
48g/24 = 2mol 2 x 120 = 240g