A- Atmosphere Flashcards
List 5 factors that affect rates of reaction
Any from: Concentration Pressure Surface area Temperature Catalyst Radiation intensity Particle size
What is special about homogeneous catalysts?
They form an intermediate compound with the reactants
How do you convert an alkane into a halogenoalkane?
Br2 (l) + sunlight (provides UV)
How do you convert an alkene into an alkane?
H2 (g) / Ni
150 degrees Celsius
5 atm
How do you convert an alkene into a halogenoalkane?
HBr/ HX (depending on halogen)
Room temperature
How do you convert a halogenoalkane into an alcohol?
NaOH (aq)
Heat under reflux
How do you convert an alcohol into a halogenoalkane?
NaBr(s)/ c.H2SO4
Heat under reflux
How do you convert a halogenoalkane into an amine?
c.NH3 (aq)
Heat in a sealed tube
How do you convert a halogenoalkane into a nitrite/ cyano?
NaCN in aqueous ethanol solution
Heat under reflux
What two things affect the changes that can occur for a chemical absorbing energy?
The chemical involved
The amount of energy involved
What does ‘energy is quantified’ mean?
with fixed levels
How much argon is in the atmosphere?
How much carbon dioxide is in the atmosphere?
0.035%
What is Planck’s constant?
6.63 X 10-34 Joules
What is the difference between dissociation and excitation?
Dissociation = Homolysis (in the context of halogens like Cl2) Excitation = Electrons jump to higher energy level but eventually drop back to original state releasing this energy
In heterolytic fission, what happens to the SHARED electrons within the covalent bond?
Both go to just one atom, turning it into an anion so that the other atom becomes a cation.
In homolytic fission, what happens to the SHARED electrons within the covalent bond?
One of the two electrons goes to each atom so that each has an unpaired electron -> radicals
What is initiation?
The production of free radicals
What is propagation?
The use and generation of radicals (on both sides of the reaction)
What is termination?
The production of new molecules through removal of radicals
What are CFCs good for?
Aerosols
Propellants
Coolant (in fridges)
Fire extinguishers
How to radicals operate/ try to fill their outer shells?
Taking an electron from another molecule (often in the form of a hydrogen)
What are the conditions of radical chain reactions?
Gas phase/ non-polar solvent
Initiation by heating/ light (UV radiation)
What is the speed of radical chain reactions?
Very fast
Where do radical chain reactions mainly take place?
Troposphere + Stratosphere
What are examples of radical chain reactions?
Combusion/ Explosions
Outline the collision theory
Reactions occur when particles of reactants collide WITH a minimum amount of kinetic energy
Any factor that increases the number of collisions PER UNIT OF TIME will increase reaction rate
What is the activation enthalpy?
The minimum energy required for a successful reaction between particles after collision
True or false? Molecules in a gas have the same amount of energy
False
What two things affect the changes that can occur for a chemical absorbing energy?
The chemical involved
The amount of energy involved
What does ‘energy is quantified’ mean?
with fixed levels
How much argon is in the atmosphere?
How much carbon dioxide is in the atmosphere?
0.035%
What is Planck’s constant?
6.63 X 10-34 Joules
What is the difference between dissociation and excitation?
Dissociation = Homolysis (in the context of halogens like Cl2) Excitation = Electrons jump to higher energy level but eventually drop back to original state releasing this energy
In heterolytic fission, what happens to the SHARED electrons within the covalent bond?
Both go to just one atom, turning it into an anion so that the other atom becomes a cation.
In homolytic fission, what happens to the SHARED electrons within the covalent bond?
One of the two electrons goes to each atom so that each has an unpaired electron -> radicals
What is initiation?
The production of free radicals
What is propagation?
The use and generation of radicals (on both sides of the reaction)
What is termination?
The production of new molecules through removal of radicals
What are CFCs good for?
Aerosols
Propellants
Coolant (in fridges)
Fire extinguishers
How to radicals operate/ try to fill their outer shells?
Taking an electron from another molecule (often in the form of a hydrogen)
What are the conditions of radical chain reactions?
Gas phase/ non-polar solvent
Initiation by heating/ light (UV radiation)
What is the speed of radical chain reactions?
Very fast
Where do radical chain reactions mainly take place?
Troposphere + Stratosphere
What are examples of radical chain reactions?
Combusion/ Explosions
Outline the collision theory
Reactions occur when particles of reactants collide WITH a minimum amount of kinetic energy
Any factor that increases the number of collisions PER UNIT OF TIME will increase reaction rate
What is the activation enthalpy?
The minimum energy required for a successful reaction between particles after collision
True or false? Molecules in a gas have the same amount of energy
False
Why does a substance feel hotter?
Particles are moving more energetically
What often happens with a 10 degrees C increase in temperature?
The rate of reaction doubles
What are the stages of homogeneous catalysis?
Reactant + reactant + catalyst = intermediate
Intermediate breaks down -> Product + reformed catalyst
What is a catalyst?
A substance that speeds up chemical reactions without being permanently changed in the process
How does a catalyst work?
Provides an alternative reaction pathway with a lower activation enthalpy than the original pathway
What is a heterogeneous catalyst?
A catalyst [substance that speeds up chemical reactions…] that is in the same phase as the REACTANTS
What are the advantages of homogeneous catalysis?
More specific
More controllable
Fewer unwanted products formed
Infinite contact between catalyst + reactants - more efficient reaction
What are the disadvantages of homogeneous catalysis?
Harder to separate from products- energy [money] required for separation
What are the advantages of heterogeneous catalysis?
Easy to separate from products
What are the disadvantages of heterogeneous catalysis?
Limited contact between catalyst + reactants - less efficient reaction
What is the catalytic cycle?
A continuous process of converting reactants into products with a catalyst
What is dynamic equilibrium?
The rate of the forward and reverse reactions are the same in a closed system
What would reactions look like on a macroscopic scale?
Nothing would appear to change
What would reactions look like on a microscopic scale?
Molecules would be constantly moving
What is ‘position’ of equilibrium describing?
A particular set of equilibrium concentrations for a reaction
What happens to the rate of the reaction during equilibrium?
It remains the same
What happens to the concentration of the reaction during equilibrium?
It is constantly changing
What happens to the rate of the reaction during equilibrium with the addition of a catalyst?
The rate of BOTH the forward and reverse reactions increase
Outline le Chateiler’s principle
If a system is at equilibrium and a change is made in any of the conditions, the system responds to counteract this change as much as possible
What is the difference between a steady state system and equilibrium
Equilibrium is always in a CLOSED system, steady state is in an OPEN system
What are the similarities between CO2 and SO2?
Oxides of G4
Same molecular formula
Neither can conduct electricity
What are the differences between CO2 and SO2?
CO2 has weaker intermolecular bonds; gas at rtp
SO2 is part of a giant covalent network; solid at rtp
SO2 has high M+B Points whereas for CO2 they’re low
CO2 is slightly soluble in water, SO2 is insoluble
CO2 has double bonds whereas SO2 has single bonds
What does ‘allotrope’ mean?
A different form/ arrangement
List 3 of the properties of covalent MOLECULAR structures:
-Consist of discrete molecules Phosphorus -> P4 Sulfur -> S8 -Strong INTRAmolecular covalent bonds -The strength of the INTERmolecular bonds determines the physical state.
List 3 examples of covalent NETWORK structures:
Boron, Silicon (Tetrahedral) , Carbon (2 of its varied forms are network structures)
List the properties of DIAMOND
Giant lattice made from carbon
Tetrahedral- joining each carbon to four others
Highly symmetrical structure
List 5 of the reasons why GRAPHITE is found in pencils
GRAPHITE
Giant flat carbon layers
Each layer is a 2D network
Each carbon is joined (strong covalent) to three other carbons; hexagonal rings formed
Fourth electron contributes to extended delocalised electron clouds forming between layers
Weakly held layers- can slide over each other
Delocalised electrons are free to move across the layer
Soft, brittle solid
What is the chemical term for ‘Bucky- Balls’?
Fullerenes (C60)
How are fullerenes formed?
Pass an electric arc between graphite rods
What colour is formed when fullerenes dissolve in benzene?
RED
Why can fullerenes dissolve in benzene?
They favour being a molecule than a network
What are ‘Buckytubes/Nanotubes’?
Elongated fullerenes
What could synthesis of longer fullerene molecules mean?
The creation of super strong, lightweight fibres
Why can C60 act as an optical limiter?
Shining light on its solution turns it darker
Absorbs more light; intensity of transmitted light is limited to a maximum value
What can Fullerenes/ C60 currently be used for?
Making protective goggles for people working with lasers
What are the main greenhouse gases?
Water vapour, carbon dioxide, methane
What does anthrogenic mean?
Caused by human activity
Why is ozone in the troposphere dangerous?
It’s harmful
Contributes to photochemical smog
Why did scientists initially reject the readings taken by the satellite mapping ozone levels?
The readings were very low so considered to be anomalous.
How is ozone destroyed?
By a homogeneous catalyst (e.g. Nitrogen oxide)
