7.2 Nuclear reactions

Question 1

Definition of amu

Answer 1

1/12 the mass of an atom of carbon-12

Question 2

Formula for energy of a particle moving at the speed of light

Answer 2

E = mc²

Question 3

Mass defect formula in words

Answer 3

𝝳 = total mass of nucleons - actual mass of nucleus

Question 4

What is binding energy of a nucleus?

Answer 4

Energy required to completely seperate the nucleons of the nucleus

Question 5

Binding energy formula

Answer 5

E = 𝝳c²

Question 6

Why does a nucleus have a mass defect?

Answer 6

When nucleons join together to form the nucleus, energy is released.
This lost energy is equivalent to a lost mass
∴ The mass of the nucleons together is less than when they were seperated

The energy given out when nucleons come together is = the energy needed to seperate them (binding energy)
∴ Binding energy = mass defect * c²

Question 7

What is an electron volt (eV)

Answer 7

Energy needed to accelerate 1 electron through a p.d. of 1 volt

Question 8

Electron volts to joules

Answer 8

1 eV = 1.6 * 10^-19 J

This is not in the data booklet

Question 9

Conversion of mass to energy (1 u = how many mega electron volts?)

Answer 9

1u = 931.5 MeVc^-2

This is in the data booklet ;)

You can ignore the c^-2 ;)

Question 10

Relationship between binding energy and atom stability

Answer 10

Higher B.E. = more stable atom

Lower B.E. = less stable atom

Question 11

How is binding energy per nucleon found?

Answer 11

Binding energy / numer of nucleons (A)

This value is then plotted against A

Question 12

Why does H have a binding energy per nucleon = 0?

Answer 12

It has only a proton. Not bound

Question 13

Element with the highest binding energy?

Answer 13

Nickel - most stable

Question 14

Which elements are unusually stable anomalies in the binding energy curve

Answer 14

Helium, Carbon, Oxygen

See image in textbook :)

Question 15

Mass difference formula

Answer 15

Δm = total mass of reactants - total mass of products

Question 16

How do we decide whether energy is released in a decay using Δm?

Answer 16

Δm>0 : energy released, decay occurs
Δm<0 : Energy must be supplied for reaction to occur

Question 17

Formula for energy released in a decay (or put it in words)?

Answer 17

E = ΔM * 931.5MeVc^-2

Just convert the mass difference to energy!

Question 18

Write an equation for the transmutation of nitrogen

Answer 18

Nitrogen-14 + alpha particle → oxygen-17 + proton

Δm < 0

Question 19

Nuclear fission

Answer 19

When a heavy nucleus splits up into lighter nuclei by being collision with a neutron

Question 20

How does a chain reaction happen

Answer 20

The neutrons produced in nuclear fission collide with more fuel nuclei, producing more neutrons which collide with more fuel nuclei and so on

Self-sustaining reaction

Question 21

Critical mass

Answer 21

given mass of fuel (e.g. U-235) needed for a chain reaction to occur to prevent the neutrons from just escaping

Question 22

Nuclear fusion

Answer 22

Joining of two light nuclei to form a heavier one with associated production of energy

Question 23

Equation for nuclear fusion

Answer 23

hydrogen-2 + hydrogen-2 → Helium-3 + neutron

H-2 is an isotope
He-3 is also an isotope

Question 24

Equation for nuclear fission with U-235

Answer 24

neutron + uranium-235 → uranium-236 + barium-144 + krypton-89 + 3 neutrons