Knowt
Chapter 12: Atom Economy and Percentage Yield
12.1-Atom Economy
Atom economy % of reactants forming useful products
A lot of reactions make more than one product
The atom economy of a reaction tells you how much of the mass of the reactants is wasted when manufacturing a chemical and how much ends up as useful product
Atom economy = relative formula mass of desired products / relative formula mass of all reactants x 100
100% atom economy means that all the atoms in the reactants have been turned into useful products, the higher the atom economy, the greener the process
Calculating the atom economy
Identify the desired product
Work out the Mr of all reactants
Work out the total M of the desired product
Use the formula to calculate the atom economy
High atom economy is better for profits and the environment
Reactions with low atom economy use up resources very quickly
At the same time, they make lots of waste materials that have to be disposed of
This makes them unsustainable
They usually aren’t very profitable
Raw materials are expensive to remove and dispose of responsibly
Reactions with highest atom economy are the ones that only have no product
The reactions have an atom economy of 100%
The more products, the lower the atom economy is likely to be
12.2-Percentage Yield
Percentage yield compares actual and theoretical yield
The amount of product you get is known as the yield
The more reactants you start with, the higher the actual yield will be
But the percentage yield doesn’t depend on the amount of reactants you started with, it’s a percentage
Percentage yield = mass of product actually made(g) / maximum theoretical mass of product x 100
Maximum theoretical mass can be calculated using balanced reaction equation
Percentage yield is always somewhere between 0 and 100%
100% yield means that you get all the product you expected to get
0% yield means that no reactants were converted into products
Industrial processes should have as high a percentage yield as possible to reduce waste and reduce costs
Yield are always less than 100%
In real life, you never get a 100% yield
Some products or reactant always gets lost along the way, and that goes fr big industrial process as well as school lab experiments
Depends on what sort of reaction it is and what apparatus is being used
Not all reactants react to make a product
In reversible reactions the products can turn back into reactant so the yield will never be 100%
For example, in the Haber process at the same time as the reaction N2 + 3H2 - 2NH3 is taking place, the reverse reaction is also happening
This means it never goes to completion
Practice Questions
In an industrial process, a factory produces 158 million grams ammonia from a theoretically possible yield of 200 million grams . Calculate the percentage yield of this process:
158,000,000/200,000,000 x 100
79%
Chapter 12: Atom Economy and Percentage Yield
12.1-Atom Economy
Atom economy % of reactants forming useful products
A lot of reactions make more than one product
The atom economy of a reaction tells you how much of the mass of the reactants is wasted when manufacturing a chemical and how much ends up as useful product
Atom economy = relative formula mass of desired products / relative formula mass of all reactants x 100
100% atom economy means that all the atoms in the reactants have been turned into useful products, the higher the atom economy, the greener the process
Calculating the atom economy
Identify the desired product
Work out the Mr of all reactants
Work out the total M of the desired product
Use the formula to calculate the atom economy
High atom economy is better for profits and the environment
Reactions with low atom economy use up resources very quickly
At the same time, they make lots of waste materials that have to be disposed of
This makes them unsustainable
They usually aren’t very profitable
Raw materials are expensive to remove and dispose of responsibly
Reactions with highest atom economy are the ones that only have no product
The reactions have an atom economy of 100%
The more products, the lower the atom economy is likely to be
12.2-Percentage Yield
Percentage yield compares actual and theoretical yield
The amount of product you get is known as the yield
The more reactants you start with, the higher the actual yield will be
But the percentage yield doesn’t depend on the amount of reactants you started with, it’s a percentage
Percentage yield = mass of product actually made(g) / maximum theoretical mass of product x 100
Maximum theoretical mass can be calculated using balanced reaction equation
Percentage yield is always somewhere between 0 and 100%
100% yield means that you get all the product you expected to get
0% yield means that no reactants were converted into products
Industrial processes should have as high a percentage yield as possible to reduce waste and reduce costs
Yield are always less than 100%
In real life, you never get a 100% yield
Some products or reactant always gets lost along the way, and that goes fr big industrial process as well as school lab experiments
Depends on what sort of reaction it is and what apparatus is being used
Not all reactants react to make a product
In reversible reactions the products can turn back into reactant so the yield will never be 100%
For example, in the Haber process at the same time as the reaction N2 + 3H2 - 2NH3 is taking place, the reverse reaction is also happening
This means it never goes to completion
Practice Questions
In an industrial process, a factory produces 158 million grams ammonia from a theoretically possible yield of 200 million grams . Calculate the percentage yield of this process:
158,000,000/200,000,000 x 100
79%
