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# Chemical equations and reactions

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### Chemical equations and reactions

1. 1. Chemical Equations and Reactions<br />Chapter 8<br />
2. 2. Describing Chemical Reactions<br />Chemical reaction<br />the process by which one or more substances are changed into one or more different substances<br />Reactants<br />the original substances<br />Products<br />the resulting substances<br />Chemical Equation<br />an equation that represents, with symbols and formulas, the identities and relative amounts of the reactants and products in a chemical reaction<br />
3. 3. Indications of A Chemical Reaction<br />Evolution of heat and light<br />Production of a gas<br />Formation of a precipitate<br />Precipitate – a solid that is produced as a result of a chemical reaction in solution and that separates from the solution<br />Color change<br />
4. 4. Characteristics of Chemical Equations<br />The equation must represent known facts<br />The equation must contain the correct formulas for the reactants and products<br />The law of conservation of mass must be satisfied<br />Coefficient – a small whole number that appears in front of a formula in a chemical equation.<br />
5. 5. Word Equation – an equation in which the reactants and products in a chemical reaction are represented by words.<br />Ex. methane + oxygen  carbon dioxide + water <br />means yield<br />Formula Equation – represents the reactants and products of a chemical reaction by their symbols or formulas.<br />Ex. CH4(g) + O2(g)  CO2(g) + H2O(g) (unbalanced)<br />
6. 6. Significance of a Chemical Equation<br />The coefficients of a chemical reaction indicate relative, not absolute, amounts of reactants and products.<br />The relative masses of the reactants and products of a chemical reaction can be determined from the reaction’s coefficients.<br />The reverse reaction for a chemical equation has the same relative amounts of substances as the forward reaction.<br />
7. 7. 4<br />1<br />1<br />2<br />2<br />1<br />2<br />4<br />1<br />2<br />4<br />2<br />1<br />2<br />4<br />1<br />2<br />4<br />2<br />1<br />4<br />Balancing Equations<br />CH4(g) + O2(g)  CO2(g) + H2O(g)<br />CH4(g) + O2(g)  CO2(g) + 2H2O(g)<br />CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)<br />
8. 8. Types of Chemical Reactions<br />Synthesis reaction (composition reaction) – a reaction where two or more substances combine to form a new compound. <br />A + X  AX where A and X are elements of compounds<br />Ex. 2Mg(s) + O2(g) 2MgO(s)<br />
9. 9. Reactions of Metals with Halogens<br />M + X  MX where M is a metal and X is a halogen.<br />Ex. 2Na(s) + Cl2(g) 2NaCl(s)<br />
10. 10. Decomposition Reactions<br />Decomposition reaction – a single reaction that undergoes a reaction that produces two or more simpler substances.<br />AX  A + X where AX is the compound and A and X are the simpler elements or compounds<br />Ex. 2H2O(l) 2H2(g) + O2(g)<br />Electrolysis – the decomposition of a substance by an electric current.<br />electricity<br />
11. 11. Δ<br />Δ<br />2HgO(s) 2Hg(l) + O2(g)<br />The means heat is needed to make the reaction happen<br />
12. 12. Single Replacement Reaction (displacement)<br />a reaction where one element replaces a similar element in a compound.<br />A + BX  AX + B where A, B, and X are elements and AX and BX are compounds<br />Ex. 2Al(s) + 3Pb(NO3)2(aq)  3Pb(s) + 2Al(NO3)3(aq)<br />
13. 13. Double-Replacement Reaction<br />Double-Replacement reactions – a reaction where the ions of two compounds exchange places in an aqueous solution to form a new compound.<br />AX + BY  AY + BX where A, B, X, and Y represent ions and AY and BX represent ionic or molecular compounds<br />Ex. 2KI(aq) + Pb(NO3)2(aq)  PbI2(s) + 2KNO3(aq)<br />
14. 14. Combustion reaction – a reaction where a substance combines with oxygen, releasing a large amount of energy in the form of light and heat.<br />Ex. 2H2(g) + O2(g)  2H2O(g)<br />
15. 15. Activity Series of the Elements<br />Activity series – a list of elements organized according to the ease with which the elements undergo certain chemical reactions.<br />