C3261 Final Flashcards
In any gas, molecules obey which distribution?
Maxell-Boltzmann Distribution
What is the most probable velocity?
The apex velocity, vp
What is the equation of the most probable velocity, vp?
vp=sqrt(2RT/M)
As the size of a gas molecule increases, what happens to the average velocity?
Decreases
What equation is mainly used to describe a real gas? (do not need to give the equation just the name)
Van der Waals equation
Triple point
all 3 phases are in equilibrium
Vapour Pressure
Below the boiling point, some molecules have enough E to escape the surface as a gas
At what point is the boiling point in terms of vapour P?
Boiling point when vapour P=external P
What do melting and boiling points largely depend on?
Intermolecular forces
Clathrate
A host-guest combination when molecules are trapped in interstitial spaces of an ice structure
Hydrate clathrate
A specific clathrate in which the host is ice
What happens when a clathrate-hydrate melts?
Guest is released as there is no bond between the host and guest
What is the packing arrangement of hydrate clathrates and what are the 2 types of cages in the structure?
Weaire-Phelan geometry
1. 2 cages with pentagonal faces
2. 6 cages with hexagonal faces
What do thermodynamics describe in a reaction?
If a reaction happens or not
What do kinetics describe in a reaction?
How fast the reaction will be
Gibb’s Free Energy equation
dG=dH-TdS
Order of entropy for states
s<l<g
With an increase in gas molecules, what happens to the entropy?
Increases
Photochemically-Driven Rxns
driven by photon energy during the daytime; highest E radiation in Earth’s upper atmosphere
What are the photochemical E relations? (2)
E=Nhv
N=avogadros number
h=Planck’s constant
v=frequency of EM radiation
c=lambda v
Ionization reactions
Occur in upper atmosphere and solar system
Ionization Energy
Minimum E required to ionize a molecule or atom
Electron Affinity
E required for addition of electrons to an atom or molecule
Hund’s First rule
The ground state has the greatest multiplicity, i.e. the highest number of unpaired electrons
Equation for multiplicity
2S+1 where S is the spin of unpaired electrons
Triplet state
Multiplicity 3 (2 unpaired electrons)
Singlet State
No unpaired electrons
Multiplicity 1
What are geological time scales measured in?
Millions (Ma) or billions of years (Ga)
Hadean Eon
Formation of Earth, starting 4.6 billion years ago and ending 4 billion years ago
Archean Eon
4000Ma-2500Ma. Earth’s crust cooled enough to allow formation of continents
Proterozoic Eon
2500Ma-540Ma. Transition to an oxygenated atmosphere and complex life appears near the end.
Phanerozoic Eon
541Ma-Present. Divided into periods.
Cambrian Period
540-485Ma. Before, living organisms were small, unicellular, and simple. Complex, multicellular organisms became more common. In this period, there was a rapid diversification of life in oceans.
Cambrian Explosion
Describes the diversification of life in oceans during the Cambrian period
Carboniferous Period
360-300Ma. Terrestrial life established (vast forests). High oxygen production resulted in highest atmospheric gas concentrations of all time.
Permian Period
300-250Ma. The largest mass extinction occurred here.
Permian-Triassic Extinction Event
Occurred around 250Ma. Largest mass extinction event in history, with 90% of marine and 70% of terrestrial species going extinct
Triassic Period
250-200Ma. Dinosaurs appear.
Jurassic Period
200-145Ma. Dinosaurs dominate most ecosystems
Cretaceous Period
145-60Ma. Dinosaur dominant and warm climate. A second peak in oxygen concentration occurs. Ended with another mass extinction, including all non-avian dinosaurs.
In 1896, Svante Arrhenius used principles of physical chem to estimate the extent of the increase in atmospheric carbon dioxide increases surface temperature. What is this known as?
Greenhouse effect
Around how much particulate mass of our galaxy is in space?
~10%
What is the relative particle density in space?
1-100atoms/m^3
Interstellar clouds
Have significantly higher densities
Diffuse interstellar clouds
Particles are mainly ionized atoms
Molecular interstellar clouds
High enough density for formation of a high proportion of molecules, neutral and ionized
Nebula
A concentration of gas and solid particles
Trihydrogen Ion
most common molecular ion in interstellar space
How is trihydrogen formed in space?
Dihydrogen is impacted by cosmic ray to produce an electron. The produced dihydrogen cation reacts with neutral dihydrogen to form the trihydrogen cation
What is the most common heteronuclear diatomic species in the universe?
HeH+ (hydridohelium ion)
What is the significance of Sagittarius B2 (SgrB2)?
Nearly every currently known molecule has been detected in this space
How are so many molecules formed in SgrB2?
Presence of small particulates provide surface for congregation of molecules and their surface rxns.
Atmosphere
Layer of gas surrounding a planet/moon/solid body
What makes an atmosphere more likely to be retained?
Strong gravitational field
Low atmospheric Temp
Jeans Escape Mechanism
Atmosphere leaks molecules into space. To escape, molecules need velocity in excess of the escape velocity of the gravitational fields. The proportion of high energy molecules in the tail of Boltzmann distribution determines the rate of atmospheric loss
What are the 2 important considerations in escape velocities?
Atmospheric temperature
Gravitational field
Solar Wind
the sun expels streams of ions from upper layers, consistent of electrons, protons, and alpha-particles.
How does solar wind impact atmospheres?
Solar wind exerts a small P where it impacts a solid body, which can erode the atmosphere
Magnetosphere
Planets with large magnetic fields have a region that allows solar wind to be deflected. This is an important factor in the retention of an atmosphere
What are the 4 gas giants
- Jupiter
- Saturn
- Uranus
- Neptune
Which of the gas giants have the greatest complexity in chemistry?
Jupiter
Great Red Spot
Vortex first observed in 1665 on Jupiter
Oval BA
Red sport formed by the combination of 3 smaller white spots in the year 2000 on Jupiter
Describe the vertical structure of Jupiter’s atmosphere
No simple transition from atmosphere to solid surface (on all gas giants). Because of low T and extreme P, there are ill-defined boundaries into supercritical hydrogen and helium.
3 Major cloud layers on Jupiter
- H2O
- NH4HS
- NH3
Where do the colors of Jovian clouds arise?
From organic species. Photodissociation of methane under high E UV reaching upper stratosphere produces many radical species that can further react to many organic compounds
What are the 3 inner rocky planets (omit earth)?
- Mercury
- Mars
- Venus
Why is mercury not important in the atmospheric chemistry discussion?
The low mass, combined with location in relation to sun and strong solar winds, and low magnetic fields, means that mercury has essentially no atmosphere.
Describe some of the conditions of Mars
Surface P around 6kPa
CO2 dominates the atmosphere
Surface T below freezing point of water
CO2 exists as solid near the poles
What has been used to establish the loss of the Martian atmosphere?
Isotopic analysis of Ar-36/38
What proportion of the Martian atmosphere is expected to have been lost?
2/3
What are the major components of the Venus atmosphere (2)?
- CO2
- N2
Why is Venus termed “Earth’s twin”?
Similarities in structure, the two planets were likely similar a long time ago
What causes the extreme temperatures on Venus?
Result of extreme radiation trapping. The surface T is around 470C, above the melting point of many metals including Pb, Sn, and Zn
As water evaporated on Venus surface, the radiation trapping ability of water led to what concept?
Runaway greenhouse effect
What different types of cloud layers exist on Venus?
Sulfuric acid
Fe2Cl6 and Al2Cl6 dimers have been identified in upper/lower clouds
What is the most common trace species on Venus?
SO2
What material exists as SCF on Venus?
CO2
Rotational E
E due to rotation of atoms or molecules. Very small separations in E levels.
Vibrational Energy
Only for molecules. Atoms within molecules are in constant vibration.
Electronic Energy
Transition of electrons in atom or molecule requires substantial E. Transition is photon in UV or vis region. Each electronic level has multiple vibrational levels.
Fundamental Vibration
Excited when one E is absorbed by molecule in its ground vibrational state
Gross Selection Rule
for IR absorption, the dipole must change. No need 4 permenant dipole, but must be a change.
Which type of molecules do not absorb IR/do not contribute to radiation trapping?
Diatomics
Types of vibrations (3)
- Symmetric stretch
- Antisymmetric stretch
- Bend
What type of vibration does not absorb in linear molecules?
Symmetric stretch
Zero Point Level
Lowest vibrational state
Bond Dissociation Energy
E required 4 bond fission
3-body collision
One component takes away excess vibrational E, becoming excited, and the other 2 react.
What are the 7 considerations in MO Theory?
- Mixing 2 atomic orbitals of same or similar E results in 2 MOS, bonding and antibonding.
- Bonding orbital E < antibonding E
- Each MO holds 2 electrons
- Lowest E orbitals fill first
- Hund’s Rule: parallel spins first
- Bond Order= bonding pairs - antibonding pairs
- Labelling (sigma and pi)
Frank-Condon Principle
No change in inter-nuclear distance during electronic transition, i.e. a molecule is frozen in its vibration
Radiationless Decay
Once in excited electronic state, molecule loses small amount of E, dropping 2 lowest vibration level.
Fluorescence
Loss of E as light as electron drops from excited electronic state to ground state
Intersystem crossing
Electron excited 2 upper singlet E state undergoes crossing which involves spin flipping
Phosphorescence
The spin reversal during intersystem crossing takes time; the delay in releasing light is known as phosphorescence
Jablonski Diagrams
Shows energy and wavelength of different E states
Spin Conservation Theory
In the products of rxn, both must be spin triplets or singlets
What are the Galactic Parameters
- Star has to be of an intermediate size
- Lifetime of a star is inversely proportional to its mass
- Location in galaxy
Tidal-Lock
When small starts have long lifetimes, their luminosity is low; the planet would have to orbit close to star. Gravitational attraction locks 1 face of the planet to face the star; cold side and hot side
Describe the galactic parameter based on location in galaxy
Explosion of large stars gives intense radiation; planets around stars near center of galaxy are more likely to be exposed to periodic radiation outbursts. Location on periphery of galaxy is much safer
Describe the time constraint on galactic parameters
Star and surrounding gas/dust envelope must have formed late in the evolution of the universe that some of the first stars exploded, scattering elements.
Current atmospheric composition on Earth
Around 78% N2, 21% O2, 1% Ar and other trace gases
Origin of Atmospheric Gases
Early earth was bombarded with ice comets; these may have been N2 and/or CO2 ice clathrates, releasing these gases as they melted
Rock vapour atmosphere
Another body impacted pre-Earth (before formation), smashing off moon, resulting in high T and creating a rock vapour atmosphere, which condensed within 2000 years.
What were the characteristics of the second original atmosphere?
Dense mixture of water vapour, CO2, and other gases. T cooled and liquid water formed, around 2Ma. The temperature and pressure conditions solubilized mineral ions faster than today. Mineral beds formed as the seas cooled and carbonates precipitated.
Faint Young Sun Hypothesis
As a star ages, the core contracts and rate of nucleosynthesis increases, i.e. luminosity increases with age.
In early times, high levels of RTGs; as the sun brightened, decreasing concentration of RTGs resulted in balancing of T on earth and came within a life supporting range.
What is Titan the moon of?
Saturn
List some characteristics of Titan
Planet-like moon
Larger than Mercury
Only non-planet to have an atmosphere
Humans could fly because of low gravity
Nitrogen rich atmosphere
What is a theory based on the formation of Titan?
Titan was once a planetoid captured by Saturn’s gravitational field. Titan’s atmosphere may be a model for early Earth
How is it theorized that Titan picked up N2 in its atmosphere?
Titan picked up N2 atmosphere by N2 clathrates from the Opik-Oort
Opik-Oort Cloud
Big belt of icy planetesimals far outside the solar system
Atmospheric Structure of Titan
Titan is very different to other atmospheres. Between 20-40km, CH4 clouds with N2 droplets. Ethane fog close to surface. Tholin haze at higher altitudes.
What are the main reactions that occur in Titan’s atmosphere? (2)
- Methane reactions
- Nitrogen reactions
Tholins
Atmosphere of Titan is orange because of wavelengths absorbed by a haze of tholinds, a liquid/solid mixture of highly unsaturated compounds with C/N/H.
What happens when tholins are warmed to room temp and water is added?
They hydrolyze to give amino acids and other building blocks of life.
Theory of life on Earth related to tholins
Life on earth started from impacts of tholin-comets into warm seas of early Earth
Inorganic Carbon Cycle
Helped early CO2 disappear; much slower and less prominent today
What did the weathering process do to silicates over millions of years?
Eroded silicate mountains
REVIEW INORGANIC CARBON CYCLE
What type of feedback cycle is weathering?
Negative feedback
Increasing T = weathering faster than volcanic output = lower atm CO2 = lower radiation trapping = planetary cooling
What do volcanic eruptions return to the atmosphere in the ICC?
CO2
What were the first living organisms
Anaerobic bacteria
Metamorphic Rock
Minerals deep in earth with high compression and heat changed to new compounds. Organic compounds cannot survive, but, graphite bands are seen in rocks, which are enriched in C-12. Rate of deposit suggests it comes from biochemical processes
Stage 1
3580Ma-2450Ma. First fossil evidence of organisms found from deposits of Dresser Formation; cyanobacteria
Stromatolites
Mats formed cylindrical aggregates. Surviving locations are in extreme environments
Thrombolites
Mats with lumps rather than layers. One of only 2 sites is in NL.
Stage 2
2450Ma-1850Ma. Atmospheric O2 increased and partial P of O2 increased
Great Oxidation Event
Shallow seas were partially oxygenated by photosynthesis; deep oceans remained anoxic
