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Energy in Chemical Reactions 1 Collision Theory of Reactions A chemical reaction occurs when • Reactants must collide. • Reactants must be oriented properly to break and form bonds. • Collision must provide the energy of activation. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 2 Activation Energy 3 4 Energy in Exothermic Reactions • heat is released. • the energy of the products is less than the energy of the reactants. • heat is a product. CaCl2 (s) H2O CaCl2 (aq) + 81 kJ Exothermic reaction in a hot pack Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 5 Energy in Endothermic Reactions • Heat is absorbed. • The energy of the products is greater than the energy of the reactants. • Heat is a reactant (added). 26 kJ + NH4NO3 (s) H2O NH4NO3 (aq) Endothermic reaction in a cold pack Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 6 Where is the energy/heat? Identify each reaction as 1) exothermic A. or 2) endothermic. N2 + 3 H2 2 NH3 + 22 kcal exothermic B. CaCO3 + 133 kcal CaO + CO2 endothermic C. 2 SO2 + O2 2 SO3 + heat exothermic 7 Chapter 9 Nuclear Radiation 8 Isotopes 9 Radioactive Isotopes • has an unstable nucleus. • emits radiation to become more stable. • can be one or more of the isotopes of an element 10 Medical Applications Radioisotopes with short half-lives are used in nuclear medicine because • they have the same chemistry in the body as the nonradioactive atoms. • in the organs of the body, they give off radiation that exposes a photographic plate (scan) giving an image of an organ. Thyroid scan 11 Some Radioisotopes Used in Nuclear Medicine 12 Exposure to Radiation • naturally occurring radioisotopes. • medical and dental procedures. • air travel, radon, and smoking cigarettes. 13 Radiation Sickness Symptoms in humans may include: Nausea, vomiting, fatigue, reduction in white blood cell count Diarrhea, hair loss, infection Death LD50 = lethal dose for ½ of population Biological damage (rem) = absorbed dose (rad) x factor (depends on radiation type) 14 Radiation Protection Radiation protection requires • paper and clothing for alpha particles. • a lab coat or gloves for beta particles. • a lead shield or a thick concrete wall for gamma rays. • limiting the amount of time spent near a radioactive source . • increasing the distance from the source. 15 Types of Nuclear Radiation Alpha () particle is two protons and two neutrons 2 protons = 2+, is positively charged Beta () particle is a high-energy electron 0e -1 Positron (+) is a positive electron 0e +1 Gamma ray is high-energy released from a nucleus 16 Alpha Decay When a radioactive nucleus emits an alpha particle, a new nucleus forms that has • a mass number that is 4 less than that of the initial nucleus. • an atomic number that is decreased by 2. 17 Alpha emission 18 Nuclear Equations Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 19 Beta Decay A beta particle • is an electron emitted from the nucleus. • forms when a neutron in the nucleus breaks down. 1n 0e + 1H 0 -1 1 20 Gamma () Radiation In gamma radiation • energy is emitted from an unstable nucleus, indicated by m following the mass number. • the mass number and the atomic number of the new nucleus are the same. • 99m here means metastable (=unstable) isotope 99mTc 43 99Tc + 43 21