1. CHAPTER 24 CHEMICAL REACTIONS

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3. CHEMICAL CHANGES A. Chemical Reactions 1. A change in which one or more substances are converted into new substances 2. The substances that react are called reactants 3. The new substances formed are called products 4. reactants -----yields-----> products NiCl 2 + 2NaOH -----yields----> Ni(OH) 2 + 2NaCl 5. Conservation of mass: the mass of the reactants always equals the mass of the products

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6. BALANCING CHEMICAL REACTIONS A. Chemical Equation: a chemical reaction that is written using formulas and symbols B. There must be the same number of atoms of each element on both sides of the equation C. Coefficients, numbers in front of the formula or symbol, are used to balance equations D. You cannot change the subscripts to balance the equation

7. E. Example: HgO -----> Hg + O 2 Hg-1 Hg-1 O-1 O-2 not balanced add coefficient 2 to both sides to get: 2HgO -----> 2Hg + O 2 Hg-2 Hg-2 O-2 O-2 equation is now balanced

8. CHEMICAL REACTIONS AND ENERGY A. Endothermic reactions require heat energy for the reaction to occur; examples: cold pack, Epsom salt in water B. Exothermic reactions give off energy, usually as heat examples: burning wood, heat packs, fireworks

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10. NUCLEAR ENERGY 1. the energy stored in the nucleus of an atom 2. Nuclear Reactions: a small amount of matter produces a large amount of energy Fusion: energy released by joining atoms’ nuclei together Fission: energy released by splitting an atom’s nucleus

11. 3. Negative effects of using nuclear energy: nuclear waste storage and disposal problems