Lecture 9 for Chem
Terms in this set (11)
A) How are the boundaries between the regions of the atmosphere determined?
B) explain why the stratosphere, more than 32km thick, has a smaller total mass than the troposphere with 16km thick?
A) boundaries between regions are at maxima and minima (peaks and valleys) in atmospheric temp profile. EG. in the trop temp decreases with altitude, while in the start, temp increases with altitude. The temp min is the tropopause boundary.
B) Atmospheric pressure in the troposphere ranges from 1.0bar to 0.4 bar, while pressure in the stratosphere ranges from 0.4 bar to 0.001 bar. Gas density (g/L) is directly proportional to pressure. The much lower density of the stratosphere means it has smaller mass, despite having a larger volume that the troposphere
What is the concentration of neon in the atmosphere in ppm
The dissociation energy of a carbon-bromine bond is typically about 201kL/mol. What is the maximum wavelength of photons that can causes C-Br bond dissociation?
A) Distinguish between photodissociation and photoionisation
B) use the energy requirements of these two processes to explain why the photodissociation of oxygen is more important than photoionisation of oxygen below about 90km
A) Photodissociation is cleavage of the 0=0 bond such that two neutral O atoms are produced: O2(g) > 2O(g)
Photoionisation is absorption of a photon with sufficient energy to eject an electron from an O2 molecule: O2(g) + hv > O2^+ +e^-
B) Photoionisation of O2 required 1205kJ/mol. Photodissociation requires only 496kJ/mol. At lower elevations, solar radiation with wavelengths corresponding to 1205 kJ/mol or shorter has already been absorbed, while the longer wavelength radiation has passed through relatively well.
Below 90Km, the increased concentration of O2, and the availability of longer wavelength radiation cause the photodissociation process to dominate.
Why is the photodissociation of N2 relatively unimportant compared to photodissociation of O2?
Photodissociation of N2 is relatively unimportant compared to photodissociation of O2 for two reasons. The bond dissociation energy N2, 941 kJ/mol, is much higher than that of O2, 495 kJ/mol. Photons with a wavelength short enough to photo dissociate N2 are not as abundant as the ultraviolet photons that lead to photodissociation of O2. Also, N2 does not absorb these photons as readily as O2 so even if a short-wavelength photon is available, it may not be absorbed by an N2 molecule
Name three common green houses gasses
Water Vapour, carbon dioxide, methane
A) why is rainwater naturally acidic, even in the absence of polluting gases such as SO4?
Rainwater is naturally acidic due to the presence of CO2 (g) in the atmosphere. All oxides of non-metals produce acidic solution when dissolves in water. Even in the absence of polluting gases such as SO2, SO3, NO, NO2, Co2 causes rainwater to be acidic. The important equilibria are:
Alcohol based fuels for cars lead to the production of formaldehyde (CH2O) in exhaust gases. Formaldehyde undergoes photodissociation, which contributes to photochemical smog:
CH2O+hv > CHO + H
Describe an effect that increased CO2 in the atmosphere will have on the world ocean.
CO2 reacts with water to form carbonic acid, H2CO3 and so as CO2 is absorbed by the world ocean the concentration of H2CO3 in the world ocean (leading to the world ocean becoming more acidic / having a lower pH). This addition H2CO3 also will impact the concentrations of HCO3 and CO3^(2)ions in the world ocean. The concentration of these ions are important as they form a buffer system that helps maintain the world oceans pH between 8.0 and 8.4
List the common products formed when an organic material containing the elements carbon, hydrogen, oxygen, sulphur and nitrogen decomposes
(a) under aerobic conditions
(b) under anaerobic conditions
A) CO3^(2), HCO3, NO3, SO4^(2) and phosphates
B) CH4 (methane), NH3 (ammonia, H2S (hydrogen sulphide), PH3 (phosphine)
What are the five common steps used in the purification of fresh water to produce drinking water?
1. coarse filtration
3. Sand Filtration