Download Unit 3d - OCCC.edu

Energy in Chemical Reactions
1
Collision Theory of Reactions
A chemical reaction occurs when
• Reactants must collide.
• Reactants must be oriented properly to break and form
bonds.
• Collision must provide the energy of activation.
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
2
Activation Energy
3
4
Energy in Exothermic Reactions
• heat is released.
• the energy of the products is
less than the energy of the
reactants.
• heat is a product.
CaCl2 (s)
H2O
CaCl2 (aq) + 81 kJ
Exothermic reaction in a hot pack
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
5
Energy in Endothermic Reactions
• Heat is absorbed.
• The energy of the
products is greater than
the energy of the
reactants.
• Heat is a reactant
(added).
26 kJ + NH4NO3 (s)
H2O
NH4NO3 (aq)
Endothermic reaction in a cold pack
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
6
Where is the energy/heat?
Identify each reaction as
1) exothermic
A.
or 2) endothermic.
N2 + 3 H2
2 NH3 + 22 kcal
exothermic
B.
CaCO3 + 133 kcal
CaO + CO2
endothermic
C.
2 SO2 + O2
2 SO3 + heat
exothermic
7
Chapter 9 Nuclear Radiation
8
Isotopes
9
Radioactive Isotopes
• has an unstable nucleus.
• emits radiation to become more stable.
• can be one or more of the isotopes of an element
10
Medical Applications
Radioisotopes with short half-lives
are used in nuclear medicine
because
• they have the same chemistry in
the body as the nonradioactive
atoms.
• in the organs of the body, they
give off radiation that exposes a
photographic plate (scan) giving
an image of an organ.
Thyroid scan
11
Some Radioisotopes Used in
Nuclear Medicine
12
Exposure to Radiation
• naturally occurring
radioisotopes.
• medical and dental
procedures.
• air travel, radon, and
smoking cigarettes.
13
Radiation Sickness
Symptoms in humans may include:
 Nausea, vomiting, fatigue, reduction in white blood cell
count
 Diarrhea, hair loss, infection
 Death
LD50 = lethal dose for
½ of population
Biological damage (rem) =
absorbed dose (rad) x factor
(depends on radiation type)
14
Radiation Protection
Radiation protection requires
• paper and clothing for alpha particles.
• a lab coat or gloves for beta particles.
• a lead shield or a thick concrete wall for
gamma rays.
• limiting the amount of time spent near a
radioactive source .
• increasing the distance from the source.
15
Types of Nuclear Radiation
Alpha () particle is two protons and two neutrons
2 protons = 2+, is positively charged
Beta () particle is a high-energy electron
0e
-1
Positron (+) is a positive electron 0e
+1
Gamma ray is high-energy released from a nucleus 
16
Alpha Decay
When a radioactive
nucleus emits an alpha
particle, a new
nucleus forms that has
• a mass number that is 4
less than that of the
initial nucleus.
• an atomic number that
is decreased by 2.
17
Alpha emission
18
Nuclear Equations
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
19
Beta Decay
A beta particle
• is an electron
emitted from the
nucleus.
• forms when a
neutron in the
nucleus breaks
down.
1n
0e + 1H
0
-1
1
20
Gamma () Radiation
In gamma radiation
• energy is emitted from an unstable nucleus,
indicated by m following the mass number.
• the mass number and the atomic number of the
new nucleus are the same.
• 99m here means metastable (=unstable) isotope
99mTc
43
99Tc
+ 
43
21