For more information, please see full course syllabus of General Chemistry

For more information, please see full course syllabus of General Chemistry

## Discussion

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## Table of Contents

## Transcription

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### Nuclear Chemistry

- Nuclear reactions involve a change of chemical composition and can be accompanied by substantial amounts of energy.
- The energy released can be in the form of alpha, beta, and gamma rays, with gamma rays being the most harmful and penetrating.
- Writing and balancing a nuclear equation follows the law of conservation of mass and charge.
- Radioactive decay processes follow first-order kinetics.

### Nuclear Chemistry

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

- Intro 0:00
- Lesson Overview 0:06
- Introduction 0:40
- Introduction to Nuclear Reactions
- Types of Radioactive Decay 2:10
- Alpha Decay
- Beta Decay
- Gamma Decay
- Other Types of Particles of Varying Energy
- Nuclear Equations 6:47
- Nuclear Equations
- Nuclear Decay 9:28
- Nuclear Decay and the First-Order Kinetics
- Summary 11:31
- Sample Problem 1: Complete the Following Nuclear Equations 12:13
- Sample Problem 2: How Old is the Rock? 14:21

### General Chemistry Online Course

I. Basic Concepts & Measurement of Chemistry | ||
---|---|---|

Basic Concepts of Chemistry | 16:26 | |

Tools in Quantitative Chemistry | 29:22 | |

II. Atoms, Molecules, and Ions | ||

Atoms, Molecules, and Ions | 52:18 | |

III. Chemical Reactions | ||

Chemical Reactions | 43:24 | |

Chemical Reactions II | 55:40 | |

IV. Stoichiometry | ||

Stoichiometry I | 42:10 | |

Stoichiometry II | 42:38 | |

V. Thermochemistry | ||

Energy & Chemical Reactions | 55:28 | |

VI. Quantum Theory of Atoms | ||

Structure of Atoms | 42:33 | |

VII. Electron Configurations and Periodicity | ||

Periodic Trends | 38:50 | |

VIII. Molecular Geometry & Bonding Theory | ||

Bonding & Molecular Structure | 52:39 | |

Advanced Bonding Theories | 1:11:41 | |

IX. Gases, Solids, & Liquids | ||

Gases | 35:06 | |

Intermolecular Forces & Liquids | 33:47 | |

The Chemistry of Solids | 25:13 | |

X. Solutions, Rates of Reaction, & Equilibrium | ||

Solutions & Their Behavior | 38:06 | |

Chemical Kinetics | 37:45 | |

Principles of Chemical Equilibrium | 34:09 | |

XI. Acids & Bases Chemistry | ||

Acid-Base Chemistry | 43:44 | |

Applications of Aqueous Equilibria | 55:26 | |

XII. Thermodynamics & Electrochemistry | ||

Entropy & Free Energy | 36:13 | |

Electrochemistry | 41:16 | |

XIII. Transition Elements & Coordination Compounds | ||

The Chemistry of The Transition Metals | 39:03 | |

XIV. Nuclear Chemistry | ||

Nuclear Chemistry | 16:39 |

### Transcription: Nuclear Chemistry

*Hi, welcome back to Educator.com.*0000

*Today's lesson from general chemistry is on nuclear chemistry. Here is the lesson overview.*0002

*We are going to start off with a brief introduction as to exactly what we mean by nuclear reaction.*0010

*Then after that, we are going to go into the types of nuclear reactions, basically the different types of what we call radioactive decay.*0015

*We are going to learn how to write and balance nuclear equations followed by studying how fast a nuclear reaction can occur.*0022

*We are going to go ahead and wrap up the lesson with a summary as always followed by some sample problems.*0033

*Nuclear reactions are different than what we have been referring to all this whole time as a chemical reaction.*0042

*In a chemical reaction, chemical identity never changes.*0051

*Carbon remains carbon; oxygen remains oxygen.*0055

*But in nuclear reactions, the chemical identity of the reactant actually changes.*0058

*We actually change one element to something totally different.*0063

*In other words, we are changing the chemical composition.*0067

*We are changing the number of protons of the original starting material during the reaction.*0072

*In general, a nuclear reaction involves starting with an isotope that is relatively unstable.*0078

*The isotope can then undergo successive decay reactions or successive decompositions forming additional unstable isotopes or nuclei of different chemical identity.*0086

*We also call these daughter nuclei.*0103

*Because this is nuclear chemistry after all, you think of some type of energy associated with it.*0109

*Each decay is often associated with the release of energy in the form of what you and I commonly refer to as radiation.*0119

*Let's now discuss the different types of radioactive decay that can occur.*0132

*The first one is called alpha decay.*0137

*Alpha decay is the weakest type of radioactive decay.*0139

*In alpha decay, energy is released in the form of what we call an alpha particle.*0144

*An example will be the decomposition of this isotope here going to 222-86-Rn plus 4-2-He.*0151

*Let's go ahead and do a brief review.*0177

*The top number is equal to Z... excuse me, the top number is equal to A.*0179

*We talked about this a long time ago.*0185

*That is going to be the atomic mass.*0187

*The bottom number is of course what we call Z.*0192

*That is just basically your atomic number.*0195

*An alpha particle is essentially a helium atom.*0199

*Sometimes you see people write it also like that.*0204

*An alpha decay is the weakest type of radioactive decay.*0209

*You can essentially stop alpha particles in its path with simple paper.*0212

*A stronger type of decay, and therefore a little more dangerous, is called beta decay*0221

*where energy is released in the form of a beta particle.*0226

*A beta particle is essentially an electron.*0229

*Let's go ahead and look at this isotope of hydrogen which is what is called tritium.*0233

*That is going to decay to a helium isotope releasing also an electron.*0241

*An electron has 0 mass but an overall charge of -1.*0247

*That is how it represents an electron or also a beta particle.*0252

*0-(-1)-beta is sometime how it is also represented.*0257

*Because a beta particle is more dangerous, you require something a little tougher to stop it.*0264

*Something like a piece of aluminum metal is sufficient to stop a beta particle in its path.*0273

*However the strongest type of decay of course is going to be what we call gamma decay.*0280

*Gamma rays are pure energy; there is no mass.*0285

*All of the energy that is released is pure energy.*0289

*Nothing is transferred to another atom as mass.*0294

*The example would be an excited cobalt isotope going to a lower state cobalt isotope and releasing just a ridiculous amount of energy.*0298

*A gamma ray is often referred to as 0-0-γ or just γ for short.*0312

*Again this is pure energy.*0321

*Of course you need something a lot more dense to stop gamma radiation.*0322

*This is what is coming out of nuclear facilities after all.*0327

*Something like concrete or something like lead is going to be the only suitable objects.*0331

*There are other types of particles of varying energy that can also be released.*0341

*One type of decay is what we call positron emission.*0347

*A positron is essentially the positive equivalent of an electron.*0353

*That is going to be represented as Β ^{1+} or as 0-1-e.*0357

*You can also have nuclear decay that releases a proton; proton emission.*0366

*Of course proton emission is basically just your hydrogen.*0376

*That is going to be 1-1-p.*0380

*Finally you can also have the release of neutrons which is going to be represented as 1-0-n.*0385

*Have a mass of 1 and a relative charge of 0.*0396

*Now that we know the different types of radioactive decay, let's go ahead and learn how to express nuclear reactions.*0401

*Just how we have seen this entire session on general chemistry, a chemical equation expresses a chemical reaction.*0408

*Similarly we are going to have what is called a nuclear equation to express a nuclear reaction.*0417

*The same principles hold though, especially the conservation of mass and the conservation of charge.*0422

*Basically the sum of the superscripts must equal each other on both sides of the equation.*0433

*The sum of the subscripts must equal also each other on both sides of the equation.*0453

*It is essentially we are balancing the equation essentially.*0463

*Let's just go ahead and take a look at three examples here.*0467

*We can have polonium-84 going to an alpha particle plus blank.*0471

*Let's go ahead and fill in what we can.*0483

*This subscript here has to be 82; subscript here has to be 207.*0485

*When you look up element 82 on the periodic table, you get lead.*0491

*Let's go ahead and do another one.*0496

*We can have sodium-11 undergoing decay to form magnesium-12 plus blank.*0498

*The subscript here has to be -1; superscript here is going to be 0.*0509

*That is going to be therefore an electron.*0519

*Excuse me... this is a typo here; let's make this 22; there we go.*0522

*Finally we can have calcium-20 combining this time with an electron.*0529

*When that happens, we are going to get 41 on top on the*0540

*right side and 19 on the bottom on the right side too.*0543

*That is element 19 which is potassium; it is relatively straightforward.*0547

*Nothing too difficult really when writing and balancing a nuclear equation.*0552

*Let's now go ahead and examine how fast a nuclear reaction can occur, basically the rate of nuclear decay.*0559

*The rate at which an unstable isotope decays is a matter of kinetics.*0569

*If you recall, kinetics as we saw was either zero, first, or second order which are the common ones.*0574

*It turns out that all radioactive decay processes follow first order kinetics.*0582

*Let's go ahead and refresh our memories and exactly what we mean by first order.*0589

*The integrated rate law for first order kinetics was the following.*0594

*The natural log of the concentration of A at some time t divided by the initial concentration of A is equal to -kt.*0599

*The half-life is equal to natural log of 2 over k.*0612

*If you all can recall what we mean by half-life, let's plot the amount on the y-axis.*0620

*On the x-axis, let's plot time.*0630

*Let's say this dot represents the initial concentration of A right here.*0632

*As it gets consumed, it is going to follow the following profile.*0640

*At some point, we are going to reach half of this initial amount.*0652

*The time that is required to reach half the initial amount, that is what we call the half-life.*0658

*We can come up with a nice equation in terms of mass where the mass*0666

*at time t is equal to the initial mass times e raised to the ?kt.*0672

*That is an equation we are going to be using when we do some sample problems.*0680

*Once again radioactive decay processes follow first order kinetics.*0686

*To summarize this very short session, nuclear reactions involve a change of chemical*0693

*composition and can be accompanied by substantial amounts of energy which is why*0698

*when nuclear reactors melt down, that is why they are so tragic.*0704

*Number two, the energy release can be in the form of what we call alpha, beta, and gamma rays,*0709

*with gamma rays of course being the most harmful and penetrating.*0715

*Writing and balancing a nuclear equation follows our most fundamental laws of conservation of mass and charge.*0719

*Finally radioactive decay processes follow first order kinetics.*0727

*Let's go ahead and tackle some sample problems.*0734

*Complete the following nuclear equations.*0737

*14-7-n plus something is going to go on to form oxygen-8 and a proton.*0740

*Let's go ahead and look at this.*0752

*Here my subscript is going to be 2; my superscript is 4.*0754

*That essentially is going to be my alpha particle.*0758

*Let's go ahead and do a second example.*0763

*Here we can have something plus a neutron going on to form Bk-97 plus an electron.*0765

*My subscript here is 96; my superscript is 248.*0780

*This is going to be a curium, Cm.*0785

*Another one can be something plus a neutron going on to form 244-96-Cm plus a gamma ray plus blank.*0790

*This should be americium-95... excuse me about that.*0812

*Now on the right side here, this is going to be 0 on top, -1 on bottom, and an electron.*0816

*Finally the last example is going to be carbon-6 reacting with a neutron.*0823

*That is going to go on to form something plus a gamma ray plus carbon-6.*0835

*I'm sorry, excuse me... the question mark is the carbon-6 to balance out everything.*0851

*That is just some straightforward examples on balancing nuclear equations.*0856

*Now finally onto sample problem two.*0862

*Potassium-40 can be used to date materials because it is presumed to have existed at the formation of the earth.*0865

*If three-fifths of the original K-40 exists in a rock, how old is the rock?*0872

*Three-fifths is the fraction remaining.*0878

*Once again three-fifths is the fraction remaining of K-40 in the rock.*0887

*We can look up the half-life of potassium-40.*0900

*The half-life of potassium-40 is 1.26 times 10 ^{9} years.*0905

*The rate constant is going to be equal to natural log of 2 over the half-life.*0915

*We are going to get 5.50 times 10 ^{-10} reciprocal years.*0922

*We can set up and use the equation M at some time t is equal to M _{0} times e raised to the ?kt.*0932

*Three-fifths is equal to the M _{0}... which is what we call 1 because at the initial point,*0941

*we have 1 if we are dealing with fractions... times e raised to the ?kt.*0953

*Solving for t, we are going to get 9.29 times 10 ^{8} years.*0959

*Once again when using fractions, don't forget, when using fractions,*0967

*the initial amount can always be represented as simply 1; 1.0.*0976

*That is our lecture on nuclear chemistry.*0993

*I will see you next time on Educator.com.*0997

0 answers

Post by Torrey Poon on July 26, 2014

Thank you sir!

1 answer

Last reply by: Professor Franklin Ow

Fri Jul 25, 2014 2:43 PM

Post by Torrey Poon on July 24, 2014

Hi Dr. Ow

I was assigned this problem from my instructor: "If you begin with a 7.52g sample of Uranium-238 and it decays for 8 half-lifes, how much of the original sample will remain?" If you could tell me how to get this problem started I'd greatly appreciate it.