Unit 3 Flashcards
What are industrial processes designed to do?
Maximise profit and minimise the impact on the environment
Environmental considerations of industrial processes
-Minimise waste
-avoid the use or production of toxins substances
-designing products which will biodegrade if appropriate
Factors influencing industrial process design
-availability, sustainability and cost of feedstock (s)
-opportunities for recycling
-energy requirements
-marketability of by-products
-product yield
Feedstock
a chemical used to make other chemicals
Raw material
a substance that is removed from the planet and processes to make the feedstock
by-product
a product also made in the reaction which isn’t the main desired product
What is percentage yield?
The percentage of product you made compared to how much you should have made
% yield=actual yield/theoretical yield x100
How can percentage yield be improved?
-avoid wastage
-use more pure reactants (as reactants contain impurities)
-use the most accurate equipment for our measurements
What is atom economy?
A measure of the proportion of reactant materials/converted in the final desired product
AT=mass of desired product/total mass of reactants x100
Excess calculations
-In a chemical reaction with more than one reactant
-A reaction stops when one of the reactants is used up
-There is (almost always) a reactant which there is far too much of—>in excess
-In order to ensure that costly reactant(s) are converted into product, an excess of less costly reactant(s) can be used
-The other reactant dictated how much product is made and the one we use for mole ration—>limiting reagent
What is the molar volume of a gas?
Its volume per mile (litres per mol)
Same for all gases at the same temperature and pressure
Value is temperature and pressure dependent
mv=V/n
Why do reaction rates have to be controlled in industrial processes?
If the rate is too low then the process will not be economically viable
If the rate is too high there will be a risk of explosion
What are the conditions required for chemical reactions to go ahead to form products
Particles collide with each other
—>
-collisions have enough energy
-correct orientation
COLLISION THEORY
5 ways to change rate of reaction
-particle size/surface area
-concentration
-temperature
-pressure (gases only)
-using catalysts
What happens when the Surface area is changed?
increase surface area—>speed of reaction increases
more surface area—>bigger area for collisions to occur
What happens when the Concentration is changed?
increase concentration—>speed of reaction increases
more particles—>more collisions—> more successful collisions
Reaction progresses—>reactants get used up—>less possible collisions—> rate decreases
What happens when the Temperature is changed?
Temperature increases—>speed of reaction increases
higher temperatures—>more energy—>faster movement—>more successful collisions
kinetic energy is increased—>pushing more molecules over the activation energy and increasing the speed of reaction
What happens when the Pressure is changed?
Pressure increases—>spread of reaction increases
high pressure—>smaller space—> more collisions—>more successful collisiobs
What is enthalpy?
-Energy stored in the bonds of molecules
-Enthalpy must be involved when a chemical reaction proceeds
-A measure of the chemical energy in a substance
-For industrial processes chemists must be able to predict the enthalpy change
-Endo may be costly as heat energy must be supplied
-Exo can lead to thermal explosions if heat energy is not removed preventing a rise in temp
Graph-reactant lower than product
The reactants need extra energy to equal the energy of the products so have to take energy from around it
-endothermic +
Graph-reactants higher than products
The reactants have too much energy to make the products so they have to disperse it
-exothermic -
🔺H=
H products - H reactants
To find energy required to make the products
What is activation energy?
Energy required for reactants to become products
Ea
The minimum energy required by colliding particles to form an activated complex and can be calculated from potential energy diagrams
What is the activated complex?
An unstable arrangement of atoms formed at the maximum of the potential energy barrier during a reaction
Catalysts
Lower the activation energy required for a reaction, making it easier to form the activated complex to form
Enthalpy does not change
Relative rate
R=1/t
Increasing temperature effect
increases kinetic energy, pushing more molecules over the activation energy and increasing the speed of reaction
Catalyst effect
Reduce activation energy, meaning now more particles have energy above the sea, so more successful collisions will lead to a faster reaction
What is the enthalpy of combustion of a substance?
The enthalpy change when one mole of the substance burns completely in oxygen
Molar bond enthalpy
The energy required to break one mole of bonds in a diatomic molecule
Mean molar bond enthalpy
The average energy required to break one mole of bonds, for a bond that occurs in a number of compounds
What can bond enthalpy we be used for?
To estimate the enthalpy change occurring for a gas phase change reaction
By calculating the energy required to break bonds in the reactants and the energy real eased when new bonds are formed in the products
What if C is given in solid form for enthalpy of combustion?
DATA BOOKLET
BOTTOM OF P11
What does Hess’ Law state?
That the enthalpy change for a chemical reaction is independent of the route taken
In a closed system, when do reversible reactions attain a state of dynamic equilibrium?
When the rates of the forward and reverse reactions are equal
At equilibrium, what are the concentrations of reactants and products?
They remain constant but are rarely equal
Which is endo and which is exo?
Bonds forming and bonds breaking
bonds forming-exo
bonds breaking-endo
What happens when you increase and decrease the temperature of an equilibrium
Increase-equilibrium shifts to the endo sidetaking in extra heat
decrease-equilibrium shifts to exo side releasing heat
What happens if you increase concentrations of products and reactant in an equilibrium?
Reactants-shifts to the right to use reactants up
Products-shifts to the left
What to look out for being added to an equilibrium?
acids
alkalis
silver nitrate and silver halides (precipitate) -> if a halide is in reaction
What do catalysts do to an equilibrium?
Speed up how quickly equilibrium is established but do not change the position
What substances are affected by pressure?
gases
What happens when you increase pressure of an equilibrium?
Shifts to the side where there are less moles of gaseous substances
What is chromatography?
A technique used to separate the components present within a mixture.
It separates substances by making use of differences in their polarity or molecular size (bigger molecules travel shorter distances)
Chromatography-How can the identity of a component be indicated?
Either by distance travelled or by the time it has taken to travel through the apparatus (retention time)
Rf=
distance travelled component/distance travelled by solvent
Why is pencil used in chromatography?
If ink was used the solvent will carry it too
Gas chromatography
Uses an inert (unreactive) gas
The larger the peak the more of the substance present
If detector is overloaded (cannot see full peak) this means we need to:
-inject less of the sample
-dilute the sample
larger samples (formula mass is larger) will appear later
What does volumetric analysis involve?
using a solution of accurately known concentration in a quantatative reaction to determine the concentration of another substance
What is titration used to determine, accurately?
The volumes of solution required to reach the end-point of a chemical reaction
What is an indicator used to show?
When the end-point of a reaction is reached. Titre volumes within 0.2cm^3 are considered concordant
What is a standard solution?
A solution of accurately known concentration
Preparation of standard solution
The weighed sample is dissolved in a small volume of deionised water in a beaker and the standard solution is transferred to a standard flask. The beaker is rinsed and the rinsing also poured into the standard flask
The flask is made up to the mark adding the last few drops of water using a dropping pipette. The flask is stoppered and inverted several times to ensure through mixing of the solution
We use deionised water because tap water contains dissolved salts that may react with our sample and affect the concentration of the solution
How to prepare a burette for titration?
rinse the burette with the solution to be put in it
fill burette above the scale with solution
filter funnel used should be removed
tap opened/some solution drained to remove air bubbles
solution run into scale reading should be made from the bottom of meniscus
