Transcript Stoichiometry Introduction

Question of the Day Rules
• You must work alone
• You may use your periodic table today
• You have 6 minutes to complete the
QOD
Good luck!!
Stoichiometry Question
• Oxygen gas can be produced by decomposing
potassium chlorate using the reaction below.
If 138.6 g of KClO3 is heated and decomposes
completely, what mass of oxygen gas is
produced?
KClO3 (s) --> KCl (s) + O2 (g)
KClO3 (s) --> KCl (s) + O2 (g)
1. Balance your equation first.
2KClO3 (s) --> 2KCl (s) + 3O2 (g)
138.6 g KClO3 x 1 mol KClO3 x
122.55 g KClO3
3 mol O2
2 mol KClO3
x
32.0 g O2
1 mol O2
= 54.286 g O2
What are we doing Today?
Nuclear Transformations Ch. 4 (EST)
• Hand in Lab (Endo & Exo)
• QOD
• Nuclear Transformations (EST)
• Practice Problems
Nuclear
Transformations
p.124 - 131
Radioactivity
• Radioactivity: Is a natural process in which an
unstable atom spontaneously transforms into
a more stable atom, or several more stable
atoms, while releasing energy in the form of
radiation (p.126)
Nuclear Stability (p.125)
• Nuclear Stability is a concept that helps to
identify the stability of an isotope. Stability:
you need to find the ratio of neutrons to
protons. (Look at table 4.25 on page 125)
• An unstable or radioactive substance may
emit three types of radiation, referred to as
ionizing radiation.
Gamma rays
• Is only made up of energy, not particles. They are neutral.
• They can easily penetrate through materials. So you need a very dense
material. (Lead)
87
38
Sr * 
87
38
Sr +  .
The * in the reaction denotes an excited nuclear state.
Alpha Particles.
• Are positive particles
• Large and Heavy, so can be stopped by a piece of paper.
• The daughter nucleus has an atomic number 2 less and an atomic mass 4
less than the parent nucleus.
• Example:
238
92
4
U  234
Th
+
90
2 He .
Beta Particles.
• Are negative particles
• Lighter then alpha particles and penetrate further
• The daughter nucleus has an atomic number 1 more and an atomic mass
the same as the parent nucleus.
• Example:
14
6
C  147 N + e- .
Later we will find there is something missing from this reaction.
Here's a plot of the activity of a radionuclide.
The initial activity was chosen
to be 1000 for this plot.
The half-life is 10 (in whatever
time units we are using).
All decay curves look like this; only the numbers on the axes will differ, depending on
the radionuclide (which determines the half-life) and the amount of radioactive
material (which determines the initial activity).
Example: radon (nasty stuff) has a half-life of
3.8 days. If you start with 1 mg of radon, after
3.8 days you will have 0.5 mg of radon.
Days
0
3.8
7.4
11.4
Radon Left (mg)
1
0.5
0.25
0.125
FUSION AND FISSION
Fusion Reactions
• 2 small nuclei release energy when they are fused together to form a
single, larger nucleus
• The process releases energy
• Energy must be supplied to create bigger nuclei
Nuclear Fission
• Energy is released in a nuclear reactor as a result of nuclear fission
• Fission is another word for splitting.
• The nucleus of an atom of a fissionable substance splits into two smaller
‘fragment’ nuclei
• This event can cause other fissionable nuclei to split, leading to a chain
reaction of fission events
• Two isotopes in common use as nuclear fuels are uranium-235 and
plutonium-239
Chain
• The additional neutrons released may also hit other uranium or
plutonium nuclei and cause them to split – even more neutrons are then
released, which in turn can split more nuclei. Called a chain reaction
Chain Reaction
Krypton
n
n
n
Uranium
n
Barium
More
decays
Chain Reaction
Chapter 4 EST Test
• Chapter 4 EST Test on Wednesday, Dec 17
• Tutorial will be on Monday, Dec. 15 at 3:15pm
That was the end of Chapter 4 (EST)
Class Work
1) In your textbook p.134
Questions: 20, 21, 22, 23
2) In your textbook p.134
Questions: 24, 25, 26, 27, 28
25