Origin of the Chemical Elements

Question 1

Evidence to support the Big Bang Theory

Answer 1

• Red shift

- CMBR

Question 2

Initial Elemental Composition of Universe

Answer 2

• 75% Hydrogen
• 25% Helium
• Small quantities of light elements e.g. lithium

Question 3

Life cycle of the sun (a yellow star) starting as a nebula

Answer 3

Nebula, Yellow Star, Red Giant Star, Planetary Nebula

Question 4

Life cycle of a blue star starting as a nebula

Answer 4

Nebula, Blue Star, Red Supergiant, Supernova explosion, Black hole or Neutron star

Question 5

A main sequence star spends most of its lifetime…

Answer 5

Undergoing nuclear fusion of hydrogen into helium

Question 6

Brown dwarf stars are failed stars because…

Answer 6

They haven’t got enough mass to get hot enough to achieve nuclear fusion

Question 7

Red dwarf stars are…

Answer 7

Main sequence stars. They are low mass and achieve nuclear fusion. Not very bright and have long lifetimes

Question 8

Red supergiant stars are formed from massive main sequence stars at end of their lifetime. What happens when they run out of helium?

Answer 8

Collapse quickly to produce giant explosion known as supernova forming elements heavier than iron

Question 9

What happens to low mass supergiant stars?

Answer 9

From nebulae where new stars start to form again

Question 10

What happens to high mass supergiant stars?

Answer 10

From neutron stars where core has collapsed

Question 11

What happens when very high mass supergiant stars collapse?

Answer 11

Becomes a black hole

Question 12

2 forces acting inside a star

Answer 12

• Inward force of gravity

- Outward force of combination of gas and radiation pressure

Question 13

What is gas pressure caused by?

Answer 13

Rapid random motion of particles in sun

Question 14

What is radiation pressure caused by?

Answer 14

Light hitting the particles

Question 15

What will happen to star if pressure in middle falls?

Answer 15

Shrink. Pressure will then rise once more until new equilibrium established with smaller star

Question 16

If pressure increases, the star will…

Answer 16

Expand

Question 17

Main sequence stars fuse what in their cores?

Answer 17

Hydrogen and Helium

Question 18

End of main sequence stage our sun will…

QWC

Answer 18

• Run out of light elements (hydrogen and helium) to fuse
• Nuclear reactions stop, pressure drops
• Nucleus shrinks, density and temperature increases allowing heavier elements to fuse
• Lighter elements fuse in shell around nucleus
• Stars like our sun don’t reach temperatures to fuse elements heavier than oxygen
• Outer layers of star pushed off by radiation pressure of core, enriching interstellar medium with heavier elements
• Dense core remains as white dwarf

Question 19

Stars heavier than our sun…

Answer 19

Have shorter lifetimes as they use their fuel up more quickly

Question 20

2 important things that happen when supernova explosion occurs

Answer 20

• Elements blasted into space to form new stars

- Material heated to billions of degrees, fusing to form heavier elements (uranium)

Question 21

The higher the binding energy per nucleon…..

Answer 21

The more stable the nuclei are

Question 22

What happens to heavier elements when they fuse?

Answer 22

Absorb energy

Question 23

What is nuclear fission?

Answer 23

Decay process where unstable nucleus splits into 2 fragments of comparable mass
(Split heavy nucleus into 2 lighter nuclei)

Question 24

Sir Fred Hoyle and others used experimental results to:

Answer 24

• Show how heavy elements could be produced

- Explain why some elements were more common than others e.g. Carbon and Oxygen

Question 25

What is nucleosynthesis?

Answer 25

Elements heavier than Helium produced in stars

Question 26

What is nucleosynthesis limited by?

Answer 26

Initial mass of main sequence star

Question 27

Scientist that described the process nucleosynthesis

Answer 27

Sir Fred Hoyle