Entropy

1. ENTROPY

2. ENTROPY

3. entropy (∆S)- a measure of disorder or randomness
entropy =  disorder
The units for entropy are J/mol·K or J/K
ENTROPY

4. ENTROPY
SECOND LAW OF
THERMODYNAMICS
the entropy of the
universe is constantly
increasing

5. ∆S solid < ∆S liquid < ∆S gas
ENTROPY

6. ΔS = Sproducts – Sreactants
When Sproducts>Sreactants, ΔS>0
ENTROPY

7. ΔS = Sproducts – Sreactants
When Sproducts<Sreactants, ΔS<0
ENTROPY

8. ENTROPY
Predict the sign of ∆S for the following reactions:
H2(g)  2 H(g) +∆S
2 H2(g) + O2(g)  2 H2O(l) - ∆S
2 NO2(g)  N2O4(g) - ∆S
C3H8(g) + 5O2(g)  3CO2(g) + 4H2O(g) +∆S
condensation of steam to liquid - ∆S

9. ENTROPY
Predict the sign of ∆S for the following reactions:
sublimation of dry ice + ∆S
2 NH3(g)  N2(g) + 3 H2(g) + ∆S
C6H12O6(s) + 6O2(g)  6CO2(g) + 6H2O(g) + ∆S
2 H2O(l)  2 H2(g) + O2(g) + ∆S
NaCl(s)  NaCl(aq) + ∆S

10. NUCLEAR REACTIONS

11. NUCLEAR REACTIONS
Nuclear reactions
release a lot of
energy.
The energy
released can be
measured as a
change in
enthalpy.

12. Radioactive decay
(4 types)
– alpha decay: emitting an alpha
particle (a helium nucleus)
α particle = 4
2He
– beta decay: emitting an
electron (an electron particle
from the nucleus)
β particle = 0
-1e
– gamma decay: emitting
electromagnetic radiation
Ϫ particle = 0
0 Ϫ
(another type is emitting a
NUCLEAR REACTIONS

13. Property Alpha (α) Beta (β) Gamma (Ϫ) neutron (n)
nature of
radiation
4
2
He
nucleus
0
-1
e
electron
high
energy
radiation
1
0
n
charge 2+ 1- 0 0
mass 4 u 0 0 1 u
penetrating
ability
stopped by 4
cm of air or a
sheet of paper
stopped by 12
cm of air or
several mm of
paper
intensity
decreases by
10% by 3 cm
of lead
NUCLEAR REACTIONS

14. Alpha decay
NUCLEAR REACTIONS

15. Beta decay
NUCLEAR REACTIONS

16. Beta decay
NUCLEAR REACTIONS

17. Gamma decay
NUCLEAR REACTIONS

18. Balancing Nuclear Reactions
The sums of the atomic numbers on both sides of
the equation must be equal (92 = 90 + 2)
The sums of the mass numbers on both sides of an
equation must be equal (238 = 234 + 4)
238
92U → 234
90Th + 4
2He
NUCLEAR REACTIONS

19. Write an equation for the emission of an alpha
particle from 226
88Ra
226
88Ra → 4
2He + 222
86 ___Rn
NUCLEAR REACTIONS

20. 234
90Th → 234
91Pa + 0
-1e
This is possible because
1
0n → 1
1p + 0
-1e
NUCLEAR REACTIONS

21. Bi
Write an equation for the emission of a
beta particle from 214
82Pb
214
82Pb → 0
-1 e + 214
83 ___
NUCLEAR REACTIONS

22. Artificial Transmutation
Alchemists never did turn lead into gold, but along the
way made many other discoveries about elements and
compounds. This was the origin of the science of
chemistry!
In artificial transmutation, a nucleus is hit by a small
nuclear particle moving at very high speed. This can
produce atoms with a desired number of protons and
neutrons.
27
13Al + 4
2He → 30
15P + 1
0n
We can now turn lead into gold!
NUCLEAR REACTIONS

23. NUCLEAR REACTIONS
Chernobyl Disaster of 1986
Abandoned city of Pripyat

24. NUCLEAR REACTIONS
nuclear fission - large nuclei are broken
in to smaller nuclei by bombardment
with a low energy neutron
–often triggers a chain reaction of events
–large amounts of energy released
(e.g. ∆H° = -1.9 x 1010
kJ/mol)
235
U + 1
n  139
Ba + 94
Kr + 3 1
n
235
U + 1
n  146
La + 87
Br + 2 1
n
235
U + 1
n  144
Cs + 90
Rb + 2 1
n
92
92
92
0
0
0
0
0
0
56
57
55
36
35
37

25. NUCLEAR REACTIONS
Describe the reaction with respect to:
1. spontaneity
2. organization of particles (beginning vs.
end of rxn)
Spontaneous and becomes highly
disorganized.
235
U + 1
n  139
Ba + 94
Kr + 3 1
n92 0 056 36

26. NUCLEAR REACTIONS
nuclear fusion - joining smaller nuclei
together to form larger nuclei
–produces a lot of energy
Stars produce heavier atoms from the
fusion of many hydrogen atoms.
2
H + 3
H  4
He + 1
n ∆H° = -1.7 x 109
kJ/mol1 1 2 0

27. NUCLEAR REACTIONS
2
H + 3
H  4
He + 1
n ∆H° = -1.7 x 109
kJ/mol1 1 2 0
Describe the reaction with respect to:
1. spontaneity
2. organization of particles (beginning vs.
end of rxn)
Not spontaneous and becomes more
organized.

28. NUCLEAR REACTIONS
Chemical and nuclear reactions tend to
spontaneously occur when the
products are lower in energy than the
reactants.
H
reaction progress
reactants
products
Reaction Spontaneity and EnthalpyReaction Spontaneity and Enthalpy

29. NUCLEAR REACTIONS
Reaction Spontaneity and EnthalpyReaction Spontaneity and Enthalpy
Chemical and nuclear reactions tend
not to spontaneously occur when the
products are higher in energy than the
reactants.
H
reaction progress
reactants
products

30. NUCLEAR REACTIONS
Nuclear reactors
convert the enormous
energy released from
fission to electrical
energy.

31. NUCLEAR REACTIONS

32. NUCLEAR REACTIONS

33. NUCLEAR REACTIONS

34. NUCLEAR REACTIONS

35. NUCLEAR REACTIONS

36. NUCLEAR REACTIONS
8.9-scale earthquake threatens safety of nuclear power plants in
Japan (March 2011)
The earthquake and tsunami knocked out cooling systems
and fuel rods began overheating

37. NUCLEAR REACTIONS
Hydrogen bomb vs. Nuclear Bomb
Nuclear bomb = fission

38. NUCLEAR REACTIONS
Hydrogen bomb vs. Nuclear Bomb
Nuclear bomb = fission

39. NUCLEAR REACTIONS
Hydrogen bomb vs. Nuclear Bomb
Hydrogen bomb = fusion

40. NUCLEAR REACTIONS
Hydrogen bomb vs. Nuclear Bomb
Hydrogen bomb = fusion

41. NUCLEAR REACTIONS
mushroom cloud anatomy:
Hot air rises, and cool air
is drawn in to replace it.
The rising hot air mass
creates a vortex within,
giving the characteristic
“mushroom” shape.