C5 + C6.1 (Acidents Happen :( ) Flashcards
What is the yield
The mass of a product made in a chemical reaction
What is theoretical yield
The maximum mass it is possible to make from the given reactants
How do you calculate theoretical yield
Find the moles in your equation and multiply the moles of your product by its mr
What is actual yield
The mass of a product that you actually make in a chemical reaction (usually less than theoretical yield)
How do you calculate percentage yield
(Actual yield ÷ theoretical yield) ×100
What range can percentage yield be between
0% and 100%
What affects percentage yield
If the reactants react in different than expected ways
The reaction may not go to completion - some of the reactants do not react
(Common in reversible reactions)
Some products may be lost when separated from the mixture to be purified
What is atom economy
A measure of how many atoms in the reactants form a desired product
If there is one product the atom economy would be 100%
How do you calculate atom economy
(total mass of desired product ÷ mass of reactants) ×100
What is a reaction pathway
Multiple reactions you can choose to create a desired product - with some being more efficient
What factors effects which reaction pathway you use
Yield of product
Atom economy of the reaction
Usefulness or otherwise, of by-products
Rate of reaction
Equilibrium position, if a reversible reaction
Cost
Environmental factors
What are by-products
Additional products made during your reaction - not the one you intended to make
How do you convert cm^3 to dm^3
Divide the cm value by 1000
What two ways can you calculate the concentration of a soluton. - g/dm^3 and mol/dm^3
Concentration = mass ÷ volume
Concentration = moles ÷ volume
C =n/v
What is a titration
A method in which a neutralisation reaction is used to determine the concentration of an acid or alkali
What are concordant results
Results within 0.1 of each other
What is a meniscus
The curve in the surface of a liquid
How do you set up a titration experiment
Use a volumetric pipette to measure out 25cm^3 of your alkali solution and put it into a conical flask
Attach you burette vertically to ensure accurate readings (preventing parallax error)
When you have filled the burette - by pouring the acid through a filter cone (25cm^3 of acid) - add indicator (2-3 drops) to your alkali
What safety equipment is needed for titrations
Safety gogles
How do you do a titration (once set up)
First take an initial burette reading, from the bottom of the meniscus and release the tap, whilst swirling the flask, until you see the indicator change colour.
Record the final reading and use them to find the total acid used.
This is your rough titration
Re-fill the burette and repeat for a more accurate titration. This time release the acid to a few cm^3 before the final value of your rough titration and slowly release the drops. Repeat this step and use your concordant results to calculate the mean titre used
You must have at least two concordant titres
How can you use results from your titration
You can use them to calculate the concentration, often in mol/dm^3
This is because you know the concentration of one liquid and the liquids used. By using the volume and the mol of your substance you can calculate the concentration
- find the mol of your known concentration
- use a balance equation to find the mol of your second liquid
Use c=m/v to find the concentration
What is molar volume
The volume occupied by one mole of a gas
24dm^3
How can you use molar volume to calculate gasses volume
Volume (dm^3) = mol × molar volume
What two things can you calculate with molar volume (gases)
The volume of a gaseous reactant or product (if you know the amount)
The amount of a gaseous reactant or product if you know the volume
What is the rate of reaction
A measure of how quickly reactants are used or products are formed
How is gas measured
Using a gas syringe
As the syringe fills, the plunger moves outwards and you can record the gas it contains (cm^3).
How does temperature affect rate of reaction.
↑temp = ↑average ke of particles
This means there are more frequent successful colisions
Increase of 10°C
Ror doubles
What is needed for a reaction to happen
If reactant particles collide
The colliding particles have enough energy to react
How can you use reaction time
Reaction time is inversely proportional to rate of reaction
Therefore by using 1/reaction time you can calculate the rate of reaction
Why are reactions faster at higher concentrations / pressure
The particles are more crowded, so there are more frequent successful collisions
How does surface area to volume ratio effect the rate of reaction (e.g as a powder)
If the surface area is greater :
More reactant particles are available for collisions
More successful collisions can occur more frequently
What is a catalyst
A substance that increases the rate of reaction without being used up
How do catalysts increase rate of reaction
They speed up the reaction by reducing the activation energy
What is collision theory
The theory that reactions can only take place when particles collide with enough energy (activation energy)
What happens to the rate of reaction, when temperature increases by 10°C
The rate of reaction will double
What is activation energy
The minimum energy needed for particles collide successfully
What is a reversible reaction
A reaction where the products can react together to form the reactants
What are the two types of reaction in reversible reactions
Forward reactions and backwards reactions
If the forward reaction is exothermic what type of reaction is the backwards reaction
It is endothermic
What is needed for a reversible reaction to be in equillibrium
It needs to be in a closed system (e.g a covered flask)
What is dynamic equillibrium
When a reversible reaction is at equilibrium, the rate of forward and backward reactions are equal
As these reactions are happening simultainiously it is a dynamic equillibrium
How do the concentrations of substances change in dynamic equillibrium
The concentrations remain constant
What is the equilibrium position
A description of the relative amounts of reactants and products in a mixture at equillibrium
Where is the equilibrium position when the reactants concentration is greater than the products
To the left
Where is the equilibrium position when the reactants concentration is lower than the products
To the right
What happens to the equillibrium position if you change the concentration of a substance in equillibrium
The equilibrium position moves away from the substance you have increased in concentration
What happens to the equillibrium position if you change the presure of a system in equillibrium
Pressure ↑ = moves in the direction of the fewest moles of gas
What happens to the equillibrium position if you change the temperature of a system in equillibrium
The equilibrium position moves in the direction of the endothermic change
What is La chatliers principle
If a system at equilibrium is exposed to a stress the system will shift to reduce that stress
Describe what happens if you increase the concentration of A
A→←B
(Reversible reaction)
The reaction becomes unbalanced so the forward reaction will speed up to use up the reactants
The equilibrium has been shifted to the right, to produce more products
Why does the equilibrium position change
As the reaction always wants to be in equilibrium, so it has to change to make the rate of reaction equal
How do you choose suitable pressures for a reaction
Using a high pressure for some reactions can speed up the rate of reaction
However working at pressures too high is expensive and can be dangerous
How are temperatures chosen for reactions
Specific temperatures are chosen based off of whether the reaction is endo or exothermic.
However s temperature cannot be too low as that will reduce the rate of reaction
What is the harber process
A process to manufacture ammonia from nitrogen and hydrogen
N2 + 3H2 →← 2NH3(g)
How are the raw materials for the harber process manufactured
Nitrogen → fractional distillation of liquified air
Hydrogen → reacting with a natural gas such as methane, with steam
What are fertilisers
Substances that replace mineral ions used by plants when the grow
What are npk fertilisers / what ion do the replace in the soil
Nitrogen → nitrate or ammonium ions
Phosphorus → phosphate ions
Potassium → potassium ions
What are the ideal conditions for the harber process
200 atmospheres (200Mpa)
Temperature of 450°C
An iron catalyst