5 Steps to a 5 AP Chemistry

of matter, as in ordinary chemical reactions.) The amount of energy that is produced can be

calculated by using Einstein’s equation E=mc^2 , where Eis the energy produced, mis the

mass converted into energy (the mass defect), and cis the speed of light. The amount of

matter that is converted into energy is normally very small, but when it is multiplied by the

speed of light (a very large number) squared, the amount of energy produced is very large.

For example: When 1 mol of U-238 decays to Th-234, 5 × 10 −^6 Kg of matter is con-

verted to energy (the mass defect). To calculate the amount of energy released:

if the mass is in kilograms, the answer will be in joules.

Common Mistakes to Avoid

1. Make sure your answer is reasonable. Don’t just write down the answer from your
   calculator.


2. Make sure your units cancel in your calculations, leaving the unit you want.


3. When balancing nuclear equations, be sure the sum of all mass numbers on the left side
   of the arrow equals the sum of all mass numbers on the right side. The same will be
   true of the sums of the atomic numbers.


4. When balancing nuclear reactions, be sure you use the atomic number of the unknown
   and not the mass number to determine the element symbol.


5. Make sure that in alpha, beta, gamma, and positron emission the particle being emit-
   ted is on the right-hand side of the reaction arrow. In electron capture, the electron
   should be on the left side of the arrow.


6. In half-life problems, don’t omit the minus sign. Watch your units.


7. In half-life problems, be sure to use the amount of isotope still radioactive as Ntand
   not the amount decayed.

 Review Questions

You have 10 minutes. You may not use a calculator. You may use the periodic table at the

back of the book. For each question, circle the letter of your choice.

Emc

E

E

=

=× ×

=× ×

−

2

682

11

5 10 3 00 10

510

()(. )kg m/s

kg m /s^22 ==× 51011 J

1. When decays, it emits 2 αparticles, then
   a βparticle, followed by an αparticle. The result-
   ing nucleus is:
   2. The formation of from occurs by:
   (A) electron capture
   (B)αdecay
   (C)βdecay
   (D) positron decay
   (E)γdecay
   3. Which of the following lists the types of radiation in
   the correct order of increasing penetrating power?
   (A)α, γ, β
   (B)β, α, γ
   (C)α, β, γ
   (D)β, γ, α
   (E)γ, β, α

92

(^234) U
90
(^230) Th
(E)^21285 At
(D)^21483 Bi
(C)^21482 Pb
(B)^22286 Rn
(A)^21283 Bi
88
(^226) Ra
Nuclear Chemistry  265
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