Chem Unit 18 Exam Notes

Front 1

Henri Becquerel

Back 1

studied uranium compounds that fluroscend. Discovered radioactivity.---> students were marie and pierre curie

Front 2

radioactivity

Back 2

the spontaneous disintegration in which small particles of matter and /or electromagnetic radiation are emitted by unstable nuclei.

Front 3

radiation

Back 3

the particles and energy produced when a nucleus undergoes radioactive decay.

Front 4

Chemical reactions

Back 4

atoms are rearranged to form new substances.
involve the release or absorption of relatively small amounts of energy.
only outer electrons are involved.

Front 5

Nuclear Reactions

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isotopes of one element are converted to isotopes of another element (chemical identity changes) (also called a TRANSMUTATION reaction.)
relatively large amounts of energy are involved.

Front 6

Natural decay

Back 6

an unstable element decays to form a more stable nucleus.

Front 7

Artificial decay

Back 7

man-made transmutations done in linear accelerators or nuclear reactors.

Front 8

Beta Decay

Back 8

a. fast moving electron formed by the decomposition of a neutron into proton and electron
b. symbol: or
c. beta particles do not penetrate aluminum foil or wood, but will penetrate paper
d. when a nucleus loses a beta particle the atomic number increases by one, the mass number remains
the same
e. Example
f. beta particles are deflected away from a negative charge and towards a positive charge

Front 9

Electron Capture/ Positron emission

Back 9

a. In both of these processes a proton is turned into a neutron
i. electron capture:
ii. positron emission:
b. when a nucleus captures an electron or gives of a positron, the atomic number decreases by one, the
mass number remains the same
c. example of electron capture:
d. example of positron emission:
i. a positron is the antiparticle of the electron (equal mass, opposite charge)
ii. symbol for positron: or
ii. when a positron and electron collide, matter is transformed into energy

Front 10

Alpha Decay

Back 10

1. alpha particles consist of two protons and two neutrons (same as a helium nucleus)
2. symbol: or
3. alpha particles are very slow moving and are stopped by paper, skin, clothing. They are very dangerous when ingested.
4. when a nucleus looses an alpha particle, the atomic number decreases by two and the mass number
decreases by four.
5. alpha particles are deflected away from a positive charge and towards are negative charge.
6. example:

Front 11

Gamma Rays

Back 11

1. Gamma rays have no mass or charge, they are electromagnetic radiation similar to X-rays, but with more energy and more penetrating power.
2. Symbol:
3. Very penetrating – can only be slowed by several feet of concrete or several inches of lead.
4. gamma rays are not affected by positive or negative charges.

Front 12

Half-Life

Back 12

the time required for one-half of the atom of a radioisotope to emit radiation and decay to the daughter product.

Front 13

Half-Life facts

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A. Every radioisotope has a characteristic rate of decay measured by its half-life.
B. Half life is the time it takes for ½ of the original radioactive atoms to decay into atoms of a new element. The other half remains unchanged.
C. After one half life, ½ or one half remain unchanged.
After two half lives, (½)2 or one fourth remain unchanged.
After three half lives, (½)3 or one eighth remain unchanged.

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random facts that we should know

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II. The stability of a radioisotope is indicated by its half life
A. The longer the half live, the more stable the isotope
B. Half lives vary from fractions of seconds to millions of years
C. Most artificially produced isotopes have short half lives.

III. Mass is converted to energy during nuclear reactions.

Front 15

Nuclear Fission

Back 15

this is the splitting of a heavier isotope into lighter isotopes
It is also accompanied by the release of large amounts of energy (nuclear binding energy)

Front 16

Nuclear Fusion

Back 16

this is the process where two lighter nuclei combine to form a heavier one.

Front 17

MOIR reaction notes

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Rate = k[A]x[B]y always concentration of reactants raised to some power.
[ ] are a shorthand method of for saying concentration in terms of molarity.
k is a constant for that reaction, called the rate constant.
x and y are exponents that can only be determined experimentally. They are refered to as “orders”.

Front 18

reaction pathways

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REMEMBER – reactions take place only if the reactant molecules collide with enough energy to cause the reactants to recombine into products

Front 19

Kinetics

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the study of the rate of chemical reactions

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Rate

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change over time

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Measuring Reaction Rates

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1. It is incorrect to say that a fast reaction can be recognized simply by the fact that it produces more product. The amount of products depends on the amount of reactant(s) used, not how quickly the reaction takes place. Amount alone can not measure rate!!!

2. Reaction rates are measured by rate of disappearance of a reactant or the rate of appearance of a product. A rate of reaction must include BOTH and amount used/formed AND the amount of time.
A. Rate of disappearance of one of the __reactants__________. Rxn Rate =


B. Rate of appearance of one of the ____products___________. Rxn Rate =

3. Properties used to measure reaction rates:

A. Disappearance or appearance of a color. Ex: Zn(s) + Cu(NO3)2(aq)  Zn(NO3)2(aq) + Cu(s).
Copper (II) nitrate is bright blue. How would you know when the reaction is complete?



B. For reactions involving gases, we measure the change in volume at constant pressure or the change in pressure at constant volume. Ex: Mg(s) + 2HCl(aq)  H2(g) + MgCl2(aq)

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collusion theory

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: - the rate of a reaction depends on the collisions between reacting particles.

A. Particles must have the proper orientation and energy (speed) when they collide in order for the collision to be successful (cause a reaction to occur).

B. Any kind of change that affects the collision will also affect the rates of a reaction.

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surface area

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: larger surface area increases the frequency at which particle collide; more successful collisions means more reactions are taken place.
Ex:
Burning a log vs. sticks

Front 24

concentration

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an increase in concentration means that there are more particles to collide producing more successful collisions.
Ex:
Running through the commons

Front 25

temperature

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an increase in temperature causes the kinetic energy of the particles to increase and to collide more often with more energetic collisions. In general: for each 10°C increase in temperature, the reaction rate doubles.
Ex:
If I increased the temp from 10 degrees to 60 degrees how much faster would the rxn be? X32 faster (2^5)

Front 26

Nature of reactants and products

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a chemical change where fewer bonds are broken and made will take less time than a more complex reaction.
Ex:
Fr (big explosion) vs. Li (little pop)

Front 27

pressure

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only affects the reaction rates where gases are involved! An increase in pressure will increase the reaction rate if the gas is a reactant, but an increase in pressure will decrease the reaction rate if the gas is a product.
Ex:
Capped vs. open soda

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catalyst

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makes the energy needed for successful collisions lower so it is easier for the reaction to occur. This increases the reaction rate.
Ex:
Enzymes!

Front 29

inhibitor

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makes the energy needed for successful collision higher so it is harder for the reaction to occur. This decreases the reaction rate.
Ex:

Food preservatives