OZ2 (Enthalpy Profiles, Maxwell-Bowzmann Curve, Radicalisation + Ozone) Flashcards
define activation energy
the minimum energy required for a reaction to take place between two colliding reactant particles
how do you find the rate of reaction on a concentration time graph
draw a tangent to the curve at the given time and find the gradient of the tangent by using change in y over change in x
how does concentration and pressure affect reaction profiles
an increase in concentration means collisions are more likely so there is a larger chance of collisions occurring with higher energy than the activation energy which increases the rate of reaction. increase in pressure has the same effect as molecules are packed close together.
how does temperature affect reaction profiles
as temperature increases, thermal energy is converted to kinetic energy
molecules move faster and further
there are more collisions with more energy which is higher than the activation energy
so more successful collisions occur increasing the rate
how does the presence of a catalyst affect reaction profiles
provides a lower activation energy so the reaction occurs quicker, increasing the rate.
what are the benefits of catalysts
they lower energy costs, temp and pressures so are cheaper
they have a higher atom economy
more sustainable as they reduce carbon dioxide emissions
what does the dip in the energy profile represent
the intermediate being formed which is less stable (higher in energy) than the products and reactants
define homogenous catalysts
catalysts in the same physical state as reactants and products
what is the maxwell-boltzmann distribution curve
the plot of the number of molecules against kinetic energy
the curve is asymptotic as it doesn’t reach the x axis because there is no maximum value for the kinetic energy of a molecule
the total area under the curve represents the total number of molecules in the sample so the area must remain constant
how does temperature affect the M-B curve
the distribution shifts to the right when temperature has increased because a greater proportion of molecules have a greater kinetic energy so a bigger proportion have energy greater to activation
how does concentration, pressure and surface area affect the M-B curve
successful collisions are more frequent but the energy of individual particles is unchanged so the shape does not change
how does the presence of a catalyst affect the M-B curve
remains unchanged in shape but the position of activation energy is shifted to the left so a higher proportion of molecules have sufficient energy to react
why do haloalkanes have polar bonds
the halogen atoms are more electronegative than the carbon
how to determine a primary, secondary or tertiary haloalkane
depends on the position of the halogen on the carbon chain
when are amines produced
when one or more H atoms in ammonia is replaced with an alkyl group
p s or t depending on how many alkyl groups are bonded to the nitrogen atom
describe the trend of boiling point and reactivity of haloalkanes
induced dipole forces increases down the group so BP increase
electronegativity of halogens decrease down the group so CF is the most polar which attracts the nucleophile in NS so you can expect CF to be the most reactive
the greater the halogen Mr, the lower the bond enthalpy so reactivity increases
explain nucleophilic substitution
the nucleophilic is an electron donor
substitution is the one functional group being replaced by a different functional group
which molecules are used to produce an alcohol, a nitrile or amines
potassium hydroxide solution, potassium cyanides, ammonia
define homolytic fission
each receives one electron from the bonded pair, single headed arrow
define heterocyclic fission
one receives both electrons from the bonded pair, forming a negative and positive ion, double headed arrow
what does UV do when alkanes react with halogens
it breaks down the halogen bonds, producing reactive intermediates (free radicals) to produce haloalkanes
what does UV cause CFCs to produce
halogen radicals which catalyse the breakdown of ozone
why are chlorine radicals considered catalysts in the breakdown of ozone
they are regenerated in the second propagation so even a small amount released is very damaging to the environment
what is ozone depletion due to and what does the ozone layer do
pollutants and greenhouse gases and it absorbs UV, most of the ozone is in the stratosphere
what is photochemical smog made by
sunlight reacting with nitrous oxides, other vehicle emissions and ozone
