Physical Chemistry Part 2 Flashcards
(42 cards)
what is a catalyst?
a catalyst is a substance that increases the rate of reaction without being used up in the process
how does a catalyst work?
a catalyst increases the rate of reaction and is not used up in the process, the catalyst lowers the activation energy and provides an alternative route for the catalyst to follow, this alternative route has an lower energy
What is a homogeneous catalyst
this is a catalyst which catalyses a reaction in the same phase as the reactants - e.g. a liquid catalyst mixed with liquid reactants or a gaseous catalyst mixed with gaseous reactants
what is a heterogeneous catalyst
this is a catalyst for a reaction which is in a different phase from the reactants, e.g. a solid catalyst used in liquid reactants
What is the economic importance of catalysts, how do they benefit us economically
- lower energy demands of the processes - they reduce costs and help the environment - less fossil fuels are needed for the required process this reduces the amount of carbon dioxide
- catalytic converters - they improve air quality by reducing toxic emissions from vehicles and prevent photo chemical smog
describe the economic importance of catalysts in regards to the Haber process
- a lot of energy is needed to break the triple bond in Nitrogen, therefore this needs a high activation energy
- iron is used to catalyse the reaction by weakening the nitrogen bonds and lowering the activation energy therefore costs
what are the disadvantages of catalysts
- toxic substances
- hard to obtain
making Ethanoic acid the old version
- important chemical that is used in the production of goods and services
- important made easily and at low cost
- most ethanoic acid was made by oxidising butane or light naphtha via hydration of ethene
- butane was heated in air using catalyst of manganese, cobalt and chromium ions to produce ethanoic acid
- this was inefficient and produced a low yield of ethanoic acid
How to make ethanoic acid the new way
- Monsanto process
- methanol reacted with carbon monoxide
- used cobalt as a catalyst and iodide ions
- orignally carried out at 300 degrees and 700 atm, there were high energy costs to generate temperature and pressure
- used rhodium as a catalyst instead - lower temperature of 150 degrees and lower pressure of 30 atm
- Cativa process superseded the Monsanto process - iridium catalyst is used - cheaper than rhodium and cuts cost - releases less carbon dioxide into the atmosphere therefore has high environmental benefits
DRAW A BOLTZMANN DISTRIBUTION GRAPH
DRAW IT
What is the Boltzmann distribution
this is the distribution of energies of molecules at a particular temperature this is often shown as a graph
why is it an average distribution of molecular energies - describe why the Boltzmann distribution graph is shaped the way that it is
- some molecules move fast and have high energy
- some molecules move slowly and have low energy
- majority of molecules have an average energy
Describe the important features of a Boltzmann distribution graph
- area under the curve is equal to the total number of molecules in the sample - area does not change with conditions
- there are no molecules in the system with zero energy the curve starts at the origin
- no maximum amount of energy for a molecule the curve gets closer to but does not cross the energy axis
- ## only molecules with a energy greater than the activation energy are able to react
Describe the effect temperature has on a rate of reaction
higher the temperatures the faster the kinetic energy of all the molecules, the more frequent the collisions and the more likely the molecule is likely to overcome the activation energy therefore the rate of reaction increases due to more successful collisions over a certain period of time
- Boltzmann graph shows a second line with a lower activation energy - draw this
DRAW HOW A CATALYST EFFECTS THE BOLTZMANN DISTRIBUTION CURVE
DRAW THIS
Describe how a catalyst effects the rate of reaction
the catalyst lower the activation energy by following an alternative route that requires a less amount of energy
- more molecules will overcome the activation energy and react so there will be a high number of successful collisions in a certain amount of time so the rate of reaction will increase
what is a reversible reaction
this is when a reaction can take place in the forward or reverse direction
What is a state of equilibrium
this is when there is no observable change in the reaction and nothing appears to be happening
- however the system is dynamic and in constant motion
A dynamic equilibrium is when….
- the concentrations of the reactants and products remain constant
- the rate of the forward direction is the same as the rate of the reverse direction
when does an equilibrium only apply
an equilibrium only applies when the system remains isolated
What is an isolated system
an isolated system is when no materials are being added or taken away and no external conditions such as temperature or pressure are being altered
when is the position of the equilibrium established
when the reaction has been occurring for a period of time - this is when the forward and backward reactions are stable and the same therefore the equilibrium is established
A reversible reaction only remains in dynamic equilibrium when…
it is isolated and in a closed system
what are the factors that affect the position of the equilibrium
- concentrations of the reactants or products
- pressure in reactions involving gases
- temperature
