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CHAPTER 21 – Nuclear Chemistry I. Review A. Ordinary Chemical Reactions versus Nuclear Reactions B. Atomic Notation Z= mass number Z E A A= atomic number II. Radioactivity and Writing Nuclear Equations A. Balancing Nuclear Reactions 1. sum of mass numbers for the reactants = sum of mass numbers for the products 2. sum of atomic numbers for the reactants = sum of atomic numbers for the products B. Common Types of Radioactive Decay 1. Alpha Radiation (Decay) – (Atomic mass of the atom is too large) samarium-146 → neodymium-142 + alpha particle 2. Beta Radiation (Decay) – (n to p ratio too high) Protactinium-234 → Uranium-234 + beta particle Net reaction: 3. Positron emission (beta positive particle) – (p to n ratio too high) Barium-133 → Cesium-133 + positron Net reaction: 4. K-electron capture reactions – (p to n ratio too high) Argon-37 + electron → Chlorine-37 Net reaction: 5. Gamma Radiation (γ) – a product of many nuclear reactions and is created by a loss of mass. Electron + Positron → γ 1 C. Zone of Nuclear Stability and Prediction of Type of Radioactive Decay D. Radioactive Series Reactions Uranium-238 decays in a series of steps that contains a combination of eight alpha and six beta steps. What is the final stable, non-radioactive product of these decay steps? E. Bombardment Reactions – Nuclear Transmutation 1. Bromine-80 + neutron → Bromine-81 + gamma radiation 2. Uranium-238 + carbon-12 → Californium-246 + 4 neutrons F. Balance the following nuclear reactions and supply the missing reactant or product 1. Nitrogen-14 + alpha particle → Oxygen-17 + __________ 2. Phosphorus-30 → Sulfur-30 + __________ 3. Beryllium-9 + alpha particle → neutron + ___________ III. Rate of Radioactive Decay-First Order Kinetics A. rate = k[N] B. ln ([N]t/[N]o) = −kt C. t1/2 = 0.693/k D. Gold-198 has a half life of 64.8 hours. How many grams of a 0.0100 gram sample of this nuclide remains after 4.00 days? 2 E. Isotope Dating 1. Rubidium-87 decays to Strontium-87 by beta emission. The half life of Rubidium-87 is 5.70 x 1010 years. Analysis of a lunar rock sample found that the ratio of Strontium-87 to Rubidium-87 is 0.0500. Estimate the age of this lunar rock. 2. A sample of wooden artifact is found to give 7.00 counts/min/gram of C due to 14C. A sample of new wood gives 15.3 counts/min/ gram of C on a Geiger counter. The half life of 14C is 5720 years. Estimate the age of this wooden artifact. IV. Energy Changes in Nuclear Reactions A. Einstein Equation: ΔE = Δmc2 c = speed of light = 2.9979 x 108 m/s B. Nuclear Binding Energy – Atoms are not the sum of parts, there is always missing mass which is called the binding energy. Calculate the binding energy per nucleon for 6Li. The atomic mass of 6Li is 6.01521 amu, mass of a proton is 1.00728 amu, mass of a neutron is 1.008665 amu and mass of an electron is 0.000549 amu. Calculate mass of 6Li = 3 x (1.00728 amu) + 3 x (1.008665 amu) + 3 x (0.000549 amu) = 6.04948 amu mass decrement = (6.04948 − 6.01521) amu = 0.03436 amu = Δm binding energy = Δmc2 = Calculate the binding energy of 56Fe per nucleon given that the nuclear mass of 56Fe is 55.92068 amu. 3 C. Energy from Nuclear Fission Calculate the energy released by the nuclear reaction below. The atomic masses are also given. Uranium-235 + neutron → Strontium-94 + Xenon-139 + 4 neutrons 235.0439 amu 1.0087 amu 93.9154 amu 138.9179 amu 1.0087 amu D. Energy from Nuclear Fusion Calculate the energy released by the nuclear reaction below. Deuterium + Tritium → Helium 4