Some reactions, like explosions, are very fast, and others, like rusting, are very slow
Rate of reaction:
Measures how much product is formed in a fixed period of time
It is calculated from the gradient, which is found with change in y ÷ change in x
Limiting reactant is the one that gets used up by the end of the reaction.
The product formed is directly proportional to the amount of limiting reactant
Rate of reaction can be increased by: - concentration: as the particles become more crowded, so there is more SUCCESSFUL collisions that take place - temperature: the particles gain more kinetic energy and they move around faster, resulting in more SUCCESSFUL collisions - pressure: this forces the particles closer together, increasing the rate of reaction
These factors increase the collision frequency, which is the amount of successful collisions between the particles each second
Larger surface area results in a higher collision frequency as the particles are more exposed, with the possibility of more collisions. Therefore, powders have a higher rate of reaction, custard powder, flour and sulfur are dangerous in factories as they are combustible for this reason
A catalyst speeds up the rate of reaction and remains unchanged at the end of the reaction
Reacting masses:
The relative atomic mass of elements is found on the periodic table
Atomic mass (Ar) is the largest number shown for each element
Conservation of mass is the total mass of the reactants equals the total mass of the products
Mass is conserved because atoms cannot be created or destroyed, the can only be rearranged into different compounds
In a chemical equation there are the same number of atoms on each side of the equation
Percentage yield & atom economy:
Percentage yield can be calculated with actual yield ÷ predicted yield x 100
Yield can be reduced by loss in filtration, evaporation, and when transferring liquids
Industrial processes require a high percentage yield: - to reduce the waste of reactants - to reduce the cost of the process
Atom economy can be calculated with Mr of desired products ÷ sum of Mr of all products x 100
Industry requires a high atom economy, to reduce production of unwanted products and to make the process more sustainable
Energy:
Bond breaking is endothermic process taking in heat
Bond forming is an exothermic process giving out heat
To decide whether ifa chemical reaction is EXO or ENDO thermic, the energy produced needs to be compared.
Energy diagrams be used to show bond energy changes: - stage 1: Energy breaks down reactant into separate atoms - stage 2: Atoms join together to form new bonds, and release energy
Energy released by fuels:
Energy transferred from fuels can be calculated with energy transferred (in J) = mass of water (in g) x specific heat capacity of water (4.2 J/g) x temperature change (in °C)
To find energy released by fuels: - measure out 1g of fuel - pour 100g water into copper calorimeter - heat water with burning fuel - measure temperature increase - repeat with other fuels to conduct a fair test
The energy released per gram can be found from the equation energy released (in j) ÷ mass of fuel burnt (in g)
Batch and continuous processing:
Batch processing advantages: - makes a fixed amount - batch can be used when needed - easy to change production to a different product
Continuous processing advantages: - makes large amounts - requires less energy to maintain - minimal labour costs
Batch processing disadvantages: - labour intensive - very expensive to run - inefficient production as not always required
Continuous processing disadvantages: - very high initial cost - inefficient process if not used constantly
Drug development:
It can take 10 years to develop a drug
To extract a chemical from a plant it is an expensive process
The process to extract a chemical from a plant: - plant is crushed to break cell walls - boiling in solvent to dissolve compounds - chromatography to separate individual compounds - isolating and purifying to test for useful compounds
It is difficult to get a licence for new drug
Safety precautions must be taken to ensure safety
Each country has strict safety laws to abide by
Long-term trials on humans are required for side effects
Patents expire before costs are recouped and others can make a new version
Allotropes:
Allotropes are different structures of the same element
Fullerenes are carbon structures, they form spheres or tubes.
Fullerenes are used to carry drug molecules around the body, and trap dangerous substances in the body
Diamond, graphite and fullerenes are allotropes of carbon
Buckminsterfullerine contains 60 carbon atoms (C60), and is a sphere of only several nanometers (10-9 metres)
Diamond and graphite:
Diamond and graphite are giant covalent structures of carbon atoms
Giant covalent bonds requires electron sharing
In diamond carbon atoms are covalently bonded to four other carbon atoms in a three dimensional tetrahedral lattice with all the outer shells being shared
In graphite every carbon atom covalently bonds to three carbon atoms in flat hexagonal layers. Breaking covelant bonds requires lots of energy
This leaves a free delocalised electron allowing graphite to conduct electricity
Diamond is the hardest natural substance, it has a high boiling & melting point. This is because the bonds form in different directions
Diamond is used for jewellery as the facets reflect light
Graphite has a high melting & boiling point, but layers can slide over each other. It is used in pencils and as a high temperature lubricant
Nanotubes can be used in catalyst systems, catalyst atoms can be added to the huge surface area of the nanotubes
Nanotubes are used to reinforce graphite in tennis rackets because they are very strong. They can also be used as semiconductors in electrical circuits