Topic 7 Flashcards
(42 cards)
Define yeild
The mass of a product made in a chemical process
Theoretical yields. In any chemical reaction :
No atoms are gained or lost
The total mass stays the same
This means that for a given mass of a limiting reactent you can make only a maximum mass of a product. This is the theoretical yield
What’s the actual yield
Is the mass of product that you really get at the end of a chemical process. This is always less than the theoretical yields
How do you calculate percentage yield
Actual yield X 100
—————
Theoretical yield
Reasons for obtaining the theoretical yield
incomplete reactions:
Reaction has not finished
Reaction reaches equilibrium
Side reactions: competing, unwanted reactions, so by-products are also made
Practical losses during the experiment:
Losses during purification eg filtration
Losses during transfers eg liquid left begin in containers
What is atom economy
A way of measuring the number of atoms wasted when making a substance
How can you calculate atom economy
Total Mr of desired products
_______________________________ x100
Total Mr of all products
What do you need to know to calculate atom economy
The balanced equation for the reaction
The relative formula masses, Mr of the products
100% atom economy
The atom economy of a process is 100% if all atoms in the reactants can be converted to the desired products. This happens when
There is only one product such as in the manufacture of ammonia :
N2 (g) + 3H2 (g) reversible 2NH3 (g)
All of the by-products are used eg as feedstock (reactants) for other processes
Industrial processes
In general, the higher the atom economy the lower its impact on the environment. Processes with high atom economies are usually preferred because they -
Produce less waste
Conserve limited resources
Such processes are more sustainable
This means that they allow us a good standard of living today without reducing the chances is this in the future
What does Avogadro law state
Equal volumes of all gases, at the same temperature and pressure have the same number of molecules
This means one mole of any gas occupies the same volume at a given temperature and pressure
The volume occupied by a gas depends on
The number of particles present
The temperature of the gas
The pressure of the gas
What’s the molar volume
The volume occupied by one mole of any gas at room temperature and atmospheric pressure (rtp)
Value for the molar volume, Vm, is
24 dm3/mol
24000 cm3/mol
Ammonium chloride decomposed when it’s heated. What’s the chemical formula
NH4CL(s) -> NH3 (g) + HCL (g)
Ammonia and hydrogen chloride combine when cool. What’s the equation
NH3 (g) + HCL (g) -> NH4CL (s)
At equilibrium
Rate of forward reaction = rate of backward reaction
When can a reversible reaction reach equilibrium?
When it’s in a closed system
A chemical equilibrium is a
Dynamic equilibrium
The forward and backward reactions keep going
What is the haber process
Is a reversible reaction between nitrogen and hydrogen to form ammonia
Atmospheric pressure and temperature for have process
200 atmospheres pressure
450C
Change in the equilibrium
TemperTure increased
What’s the effects?
Moves in the direction of an endothermic reaction
Rate of reaching equilibrium is increased
Pressure increased in equilibrium
What are the effects
Moves in the direction of the fewest molecules of gas Rate increased (if reacting gases are present) to equilibrium
Concentration of a reacting substance is increased in an equilibrium.
How does this effect?
Moves in the direction away from the reacting substance
Rate of reaching equilibrium increases
