Chapter 5 - Kinetics Flashcards
define collision theory
the idea that for a reaction to take place, particles must collide with the required energy or more, and with the right orientations
more collisions will result in a greater rate of reaction
what factors affect the rate of reaction
catalysts
temperature
concentration (liquids)
pressure (gases)
surface area (solids)
define activation energy
the minimum energy required for a particle to start breaking bonds
the minimum energy for a reaction to take place
what is a transition state
the species that exist on the peak of a curve on an enthalpy diagram
at this point, some bonds are made and some are being broken
describe the motion of particles in any gas or solution
particles all move with different speeds, however their average speed depends on the temperature of the solution
what are the axis of a maxwell boltzmann distribution graph
the y axis is the fraction of particles with energy E
the x axis is the energy E
what can be concluded from a maxwell boltzmann distribution graph
no particles have zero energy
most have intermediate energies ( the peak of the cureve)
few particles have high energies
the energy a particle can have has no upper limit
what can be concluded from marking the Ea on a maxwell boltzmann distribution graph
the number of particles with or more than the required Ea to react
this shows the proportion of particles that will react when the activation energy is supplied
how does temperature change the appearance of a maxwell boltzmann distribution graph
at higher temps, the peak is lower and moves to the right
how will using a catalyst look like on an enthalpy diagram and on a maxwell boltzmann distribution graph
the peak (the transition state) will be lower on an enthalpy diagram, however the overall energy change will not change
the line showing Ea will be more to the left, hence the area beneath the graph to the right of the Ea will be greater and a greater proportion of particles will be able to successfully collide
what changes about the energy distribution of the particles when the temperature is higher and why is this important for rares of reaction
a higher proportion of particles have the required Ea to react
this is the reason for why increasing the temp will increase the rate of reaction
what is a catalyst
a substance which increaces the rate of reaction without being chemically changed or used up
how do catalysts work
they provide an alternate reaction pathway which requires less activation energy
what catalyst is used in the haber process
iron
what catalyst is used in making nitric acid
platinum and rhodium
what catalyst is used in hardening of fats with hydrogen
nickel
what catalyst is used in cracking hydrocarbon chains from crude oil
aluminium oxide and silicon dioxide zeolite
what catalyst is used in catalytic converters in cars
platinum and rhodium
what catalyst is used in esterification
H^+ ions
how do catalytic converters work
in adsorption, the gases bond to the metal atoms which hold the molecule sin the right positions to react together.
then after reacting the products break away from the metals in desorption
what is a zeolite
a mineral which has an open pore structure so that it can trap singular molecules in small spaces which can change their structure and reactivity
how are fats hardeened
nickel is added to unsaturated fats then hydrogen is bubbled through the fat which hardens it to the desire of the manufacturer
the nickel is then filtered off
why are CFCs harmful
they are harmful to the ozone layer because they are unreactive and stay in the atmosphere for a long time until they decompose into chlorine atoms
chlorine acts as a catalyst in the breaking down of O3 molecules - ozone
what does the ozone layer do, why is it important
it acts as a sheild which prevents the suns UV rays from heating the earths surface too much
in essence it makes the earth habitable
explain how homogenous catalysts work generally
Homogeneous catalysts provide an alternative reaction route, with lower activation energy than the original reaction, causing the reaction rate to increase. Homogeneous catalysts do this by reacting to form an intermediate, which reacts further to form the final products of the reaction. The homogeneous catalyst is regenerated, meaning that it is not used up during the reaction.
explain how heterogeneous catalysts work generally
First, reactant molecules adsorb to the surface of the catalyst at an active site. Second, the reaction takes place on the surface of the catalyst. Finally, the products detach from the catalyst’s surface in a process called desorption.
