Chemistry is the language of life. Life is based on atoms, molecules and complex chemical reactions — Physical Chemistry — Kinetics Chemistry Question
“A brief history” of life in the universe
Chemistry is the language of life. Life is based on atoms, molecules and complex chemical reactions involving atoms and molecules. It is only natural then to ask where atoms came from. According to a widely accepted model, the universe began about 15 billion years ago in a big bang and has been expanding ever since. The history of the universe as a whole can be viewed in terms of a series of condensations from elementary to complex particles as the universe cooled. Of course, life as we know it today is a special phenomenon that takes place at moderate temperatures of the Earth.
Light elements, mostly hydrogen and helium, were formed during the first several minutes after the big bang in the rapidly expanding and, therefore, rapidly cooling early universe. Stars are special objects in space, because temperature drop is reversed during star formation. Stars are important in chemistry, because heavy elements essential for life are made inside stars, where the temperature exceeds tens of millions of degrees.
The temperature of the expanding universe can be estimated simply using:
T = 10
1/2
1 10 t
×
where T is the average temperature of the universe in Kelvin (K) and t is the time (age of the universe) in seconds. Answer 1.1 through 1.4 with one significant figure. Round off if you want.
Estimate the temperature of the universe when it was 1 second old at which time the temperature was too high for fusion of protons and neutrons into helium nuclei to occur.
Model Answer
1.1 T = 1×1010 / (1)1/2 = 1×1010 K (10 billion degrees)
Estimate the temperature of the universe when it was about 3 minutes old and the nuclear synthesis of helium was nearly complete.
Model Answer
1.2 T = 1×1010 / (180)1/2 = 0.7×109 ≈ 1×109 K (1 billion degrees)
Estimate the age of the universe when the temperature was about 3,000 K and the first neutral atoms were formed by the combination of hydrogen and helium nuclei with electrons.
Model Answer
1.3 t = [1×1010 / (3×103)]2 s = 1×1013 s = 3×105 yr
The first stable molecules in the universe were possible only after the temperature of the expanding universe became sufficiently low (approximately 1,000 K) to allow atoms in molecules to remain bonded. Estimate the age of the universe when the temperature was about 1,000 K.
Model Answer
1.4. t = (1×1010 / 1×103)2 s = 1014 s = 3×106 yr
Estimate the average temperature of the universe when the universe was about 300 million years old and the first stars and galaxies were born.
Model Answer
1.5 100 K
Estimate the temperature of the universe presently and note that it is roughly the same as the cosmic microwave background measurement (3 K).
Model Answer
1.6 10 K
Order the following key condensations logically, consistent with the fact that over 99 % of atoms in the expanding universe are hydrogen or helium.
(a) – ( ) – ( ) – ( ) – ( ) – ( ) – ( ) – ( ) – ( ) – ( )
a. quarks → proton, neutron
b. 1×1014 cells → human being
c. H, C, N, O → H2, CH4, NH3, H2O (in interstellar space)
d. proton, helium nucleus + electron → neutral H, He atoms
e. proteins, nucleic acids, membrane → first cell
f. proton, neutron → helium nucleus
g. H2, He, CH4, NH3, H2O, dust → solar system
h. H, He atoms → reionization, first generation stars and galaxies
i. proton, helium nucleus (light elements) → heavy elements such as C, N, O, P, S, Fe, U; supernova explosion
j. H2, CH4, NH3, H2O, etc. → amino acids, sugars, nucleotide bases, phospholipids on Earth
Model Answer
1.7 (a) – ( f ) – ( d ) – ( h ) – ( i ) – ( c ) – ( g ) – ( j ) – ( e ) – ( b )