AST251H1 Lecture 7: AST 251 Lecture 7

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magentaduck547

2 May 2012

School

UTSG

Department

Astronomy & Astrophysics

Course

AST251H1

Professor

H.Pfeiffer

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Document Summary

How did it start: the essential organic materials (co2, ch4, water, h2, n2) were there, comets and meteorites may have brought more complex organic molecules from outer space and water, steps needed: Formation of organic molecules: amino acids and nucleotides. Joining of large molecules into proteins and nucleic acids. Aggregation into droplets with different chemical properties than the environment. Replication and heredity rna and dna. Earth a water planet: ocean crust sinks back into mantle, continental crust floats on top and grows over time, the total amount of water on earth is 0. 1% of its mass. Compare with outer solar system 20: height variation of surface +8km above, -5km below the sea level. With twice the water (0. 2% of mass), oceans would cover all the land. Early ideas about the origins of life: pungent ponds of tidal water full of stuff . Vulnerable to uv radiation (no oxygen, hence no ozone layer)

Related Questions

14.1 a) The atmospheric pressure of Mars is about 600 Pa and thesurface temperature varies from -30 Â°C to -100 Â°C. The atmosphereof the planet is 95.3% carbon dioxide (CO2) and about 0.03% watervapor. The polar ice caps contain both CO2 ice and water ice. Couldthere be liquid CO2 on the surface of Mars? Could there be liquidwater? You need to provide quantitative justifications for youranswers. (What is
the key piece of data you need for your conclusion?) For more onwater on Mars, see
http://www.daviddarling.info/encyclopedia/M/Marsatmos.html
http://www.timesonline.co.uk/tol/news/science/space/article6849802.ece

b) What is the escape speed from the Earth? A gas moleculetravelling away from Earth near the outer boundary of the Earthâsatmosphere would, at this speed, be able to escape from the Earthâsgravitational field. At what temperature is the rms speed of (i)oxygen molecules, and (ii) helium atoms equal to the escape speed?(iii) Can you see why our atmosphere contains oxygen but nothelium?

Fill in the nine gaps in this table.
Symbol B
Protons 19
Neutrons 20
Electrons 18
Mass number 11 40

Identify the unknown particle (X) in the following equations fornuclear decay, and state whether each process is alpha decay, betadecay, or gamma decay. (Type your answer according to this format:4 2 He represents . Use gamma to enter ?.)
(a) ? X + -
X =

(b) ? + X
X =

(c) ? + X
X =

Actinium-225 () undergoes alpha decay.
(a) Write the equation. (Enter the mass number in the first raisedbox, the atomic number in the second lower box, and the element,with charge if necessary, in the third box.)
? + He

(b) The daughter formed in part (a) undergoes beta decay. Write theequation. (Enter the mass number in the first raised box, theatomic number in the second lower box, and the element, with chargeif necessary, in the third box.)
? + e

Classify each of the following materials as an element, compound,heterogeneous mixture, or homogeneous mixture.
(a) concrete
element
compound
heterogeneous mixture
homogeneous mixture

(b) clear apple juice
element
compound
heterogeneous mixture
homogeneous mixture

(c) nitrogen
element
compound
heterogeneous mixture
homogeneous mixture

(d) ozone
element
compound
heterogeneous mixture
homogeneous mixture

Refer to the figure below. Find the approximate solubility (g/100 gwater) of sugar at 20Â°C.
g/100 g of water

Give the symbol for each of the following elements.
(a) lead

(b) sodium

(c) oxygen

Give the name of each element.
(a) Cu

(b) Bi

(c) Ti

Volcanoes emit much hydrogen sulfide gas, H2S, which reacts withthe oxygen in the air to form water and sulfur dioxide, SO2. Every53 tons of H2S reacts with 75 tons of oxygen and forms 28 tons ofwater. How many tons of SO2 are formed?

An antacid tablet weighing 0.939 g contained calcium carbonate asthe active ingredient, in addition to an inert binder. When an acidsolution weighing 56.233 g was added to the tablet, carbon dioxidegas was released, producing a fizz. The resulting solution weighed56.954 g. How many grams of carbon dioxide were produced?

Calculate (to the nearest 0.1 u) the formula mass of thesecompounds.
(a) sodium phosphate, Na3PO4
u

(b) methane, CH4
u

(c) silver cyanide, AgCN
u

Calculate (to the nearest 0.1 u) the formula mass of thesecompounds.
(a) silver carbonate, Ag2CO3
u

(b) calcium bromide, CaBr2
u

(c) magnesium hydroxide, MgOH
u

Balance these chemical equations. (Use the lowest possiblecoefficients.)
(a) O2 + N2H4 ? H2O2 + N2

(b) Sr + H2O ? Sr(OH)2 + H2

(c) NH3 + O2 ? N2 + H2O

(d) Al + Fe3O4 ? Al2O3 + Fe

(e) Fe(OH)2 + O2 + H2O ? Fe(OH)3

(f) Pb(NO3)2 ? PbO + NO2 + O2

(a) Calcium and chlorine react to give calcium chloride in acombination reaction. Write and balance the equation. (Type youranswer using the format CO2 for CO2. Use the lowest possiblecoefficients.)

Ca + ?

(b) Heating decomposes Na2CO3 to sodium oxide and carbon dioxide.Write and balance the equation. Type your answer using the formatCO2 for CO2. Use the lowest possible coefficients.)

Na2CO3 ? + CO2

Write and balance the reaction for the complete combustion ofmethanol, CH3OH. (Type your answer using the format CO2 for CO2.Use the lowest possible coefficients.)

1. The Jeans instability occurs when
Athe pressure in a gascloud is less than its gravitationalforce.
Bthe pressure in a gascloud is greater than its gravitationalforce.
Cthe temperature in acollapsing cloud is hot enough to fuseHydrogen.
Dthe temperature in acollapsing cloud is hot enough to fuse Helium.

2. At what stage in its life does a star pass through theprotostarphase?
AAfter condensationbut before nuclear reactions begin in itscore.
BWhile it is convertinghydrogen into helium in its core.
CAfter nuclear reactionsend in its core, but before the red giantphase.
DWhen it is expanding insize as a red giant or supergiant.

3. The characteristics of an open cluster of stars are
Aa few hundredmembers, often very young and still embedded in thegas and dustfrom which they were formed.
Bmany thousand members, ofdifferent ages.
Ca few dozen members, theremnant of a globular cluster of starsfrom which most of themembers have escaped.
Dhundreds of thousands ofmembers, all very old, and no or verylittle interstellar gas anddust.

4. What is a protostar?
AA star near the endof its life, before it explodes as asupernova.
BA sphere of gas aftercollapse from an interstellar cloud butbefore nuclear reactionshave begun.
CA small interstellarcloud, before it collapses to become astar.
DA shell of gas left behindfrom the explosion of a star as asupernova.

5. What is an H II region?
AA region of hot,ionized hydrogen around one or more O and Bstars.
BA region of molecularhydrogen inside a giant molecularcloud.
CA region of neutral,atomic hydrogen in interstellar space.
DA region of gas and dustformed by the explosion of a massive star.

6. The total time that the Sun will spend as a main sequencestaris
Aabout 4.5 millionyears.
Bat least 200 billion yearsyears.
Cabout 1 millionyears.
Dabout 10 billionyears.

7. How is a star's lifetime related to its mass?
AThe lifetimes ofstars are too long to measure, so it is not knownhow (or if) theirlifetimes depend on mass.
BA star's lifetime does notdepend on its mass.
CLower-mass stars runthrough their lives faster and have shorterlifetimes.
DHigher-mass stars runthrough their lives faster and have shorterlifetimes.

8. In the Hertzsprung-Russell diagram, how does the position ofatypical star change while it is at the main sequence phase ofitsevolution?
AA star's position onthe main sequence is determined only by itsmass and not its age,and so, stars do not move along the mainsequence duringevolution.
BMassive stars (4 solarmasses) move toward the upper left as theirluminosity increases,while lower-mass stars move toward the lowerright as theirtemperature decreases.
CStars move from upperright to lower left while they are on themain sequence.
DStars move from upper leftto lower right while they are on themain sequence.

9. Why does the core of the Sun contain more helium andlesshydrogen than does the surface of the Sun?
AHelium condenses moreeasily so, when the Sun was forming the corebecame helium-rich;vast quantities of hydrogen were added onlyafter the core becamemassive enough.
BThe hydrogen has beenlifted out of the core by the Sun's magneticfield.
CHelium is heavier thanhydrogen, and has sunk toward the center ina process of chemicaldifferentiation.
DThermonuclear reactionshave converted much of the originalhydrogen in the core intohelium.

10. In terms of nuclear reactions, what is the next stage ofastar's life after the end of hydrogen burning in thecore?
AHydrogen burning ina thin shell around the core.
BHelium burning in thecore.
CCarbon burning.
DDeath (it becomes eithera supernova or a white dwarf).

AST251H1 Lecture 7: AST 251 Lecture 7

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