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how can rate of reactio be quantitatively determined
by how quick a reactant disappears or how quickly a product appears
what are the 3 main principles of collision theory
molecules must collide successfully to cause chemical change
molecules must collide with sufficient kinetic energy to overcome activation energy
molecules must collide with a suitable orientation
how does state of matter affect reaction rate
gas will react faster than liquid and solid generally
this is due to the fact that in solids and lqiuids other changes must occur before it can react
(i.e. solid must melt)
however a gas can readily react so the reaction occurs quicker
why do aqueous ions tend to react faster than other states of matter
in an ionic solid the strong ionic bonds is hard to separate, requiring energy to be broken
however in solution the ions are already dissociated and the ions only need to collide for reaction to occur
which bond type reacts fastest
ionic is generally quicker than molecular compounds
how does bond strength and number affect reaction rate
the stronger a bond, or the more bonds that exist, the longer the reaction will take
how does concentration affect reaction rate
increasing concentration will increase rate because there is a higher chance of a collision occuring
this is because more particles exist in the same volume
which states can increase concentration
aqueous solutions and gases
NOT solids or liquids
how does gas pressure affect reaction rate
increasing pressure will effectively increase concentration and speed up the reaction
how does particle size affect reaction rate
breaking a substance into smaller pieces increases the surface area to volume ration and therefore increases reaction rate
this is because there is a higher chance of a collision occuring and reacting
how does temperature affect reaction rate
an increased temperature increase the average kinetic energy of a substance which increases the chance of a collision
the increased kinetic energy also means more molecules have sufficient energy to overcome the activation energy
define a catalyst
a substance which upon contact with reactants changes the rate of reaction without being chemically changed itself
how do catalysts improve rate of reaction
they provide an alternate pathway with a lower activation energy and help break chemical bonds in reactants
a lower actiation energy means that at the same temperature, more molecules will have sufficient energy to overcome the acitvation energy
what occurs in engines in real life
there is incomplete combustion because there is not adequate time for a full reaction to occur
this means there is carbon monoxide and volatile organic compounds, as well as nitrogen oxides
what does a catalytic converter aim to do
clean exhaust gases from the engine, to reduce air pollution and reduce ozone gas emissions to therefore help the envrionment
describe the structure of a catalytic converter
there is a catalyst mixture of platinum, rhodium, palladium and aluminium oxide coated onto a honeycomb structure
the porous metal provides a large surface area
where is a catalytic converter located
slightly behind the engine and before the exhaust
what reactions occur in the catalytic converter
hydrocarbons oxidate into carbon dioxide and water
carbon monoxide oxidates into carbon dioxide
nitogen oxides reduce into nitrogen and oxygen
which reaction do 2 way catalytic converters not carry out
they do not reduce the nitrogen oxides
define an enzyme
a biological catalyst which is hihgly specific
how do enzymes work
the specific substrate attaches to the enzyme active site to form enzyme substrate complex, by weak intermolecular forces
bonds quickly rearrange to from new products ands then release
enzyme is left unchanged
how do catalysts improve sustainability
catalyst reduce energy required and minimise environmental impact
because catalysts remain unchanged they also last a long time, reducing the amount which needs to be used
why are nanoparticles a promising catalyst
because they have such a high surface area to volume ration, meaning maximum reaction can occur on a smaller volume and therefore its cheaper
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