Atom Economy and Percentage Yield Flashcards
What is the theoretical yield of a product?
The mass of the product that should be made in a reaction if no chemicals are lost in the process.
Why is the actual mass of product (actual yield) always less than the theoretical yield?
Some chemicals are always lost, e.g some of the solution always gets left on filter paper, or is lost during transfers between containers.
What is the percentage yield?
The actual amount you collect written as a percentage of the theoretical yield. It tells you how wasteful a PROCESS is.
Why doesn’t percentage yield measure how wasteful the REACTION is?
A reaction that has 100% yield could still be very wasteful if a lot of the atoms from the reactants wind up in by-products rather than desired products.
What is atom economy?
A measure of the proportion of reactant atoms that become part of the desired product in the balanced chemical equation.
Sum of the molecular masses of the desired product ÷
sum of molecular masses of all products × 100
Equation for percentage yield?
Percentage yield = actual yield/theoretical yield x 100
Equation for atom economy?
% atom economy = molecular mass of desired product/ sum of molecular masses of all products x 100
What is the atom economy for addition reactions?
Always 100% since no atoms are wasted- the reactants combine to form a single product.
What is a substitution reaction?
One where some atoms from one reactant are swapped with atoms from another.
This type of reaction always results in at least two product- desired and by.
Why do companies in the chemical industry often choose reactions with high atom economies?
There are environmental and economic benefits.
Low atom economy means a lot of waste is produced.
It costs money to separate desired product and more money to dispose waste products safely.
Waste of money is high proportion of reactants end up as waste.
Low atom economy reactions are less sustainable- many raw materials are in limited supply.
