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Chemical Reactions I. Reactions and Equations A. Chemical reactions

Chemical Reactions I. Reactions and Equations A. Chemical reactions 1. Atoms of one or more substances are rearranged into different substances 2. Examples are breaking down food, synthetic products, power for vehicles 3. Evidence of a chemical reaction

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Chemical Reactions I. Reactions and Equations A. Chemical reactions

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  1. Chemical Reactions I. Reactions and Equations A. Chemical reactions 1. Atoms of one or more substances are rearranged into different substances 2. Examples are breaking down food, synthetic products, power for vehicles 3. Evidence of a chemical reaction a. Change in temperature (heat lost or gained) b. Change in color c. Production of an odor d. Gas bubbles produced (gas) e. Precipitate produced (solid)

  2. B. Chemical equations 1. Used to represent chemical reactions 2. Equations indicate how the reaction occurs, not amounts a. Arrows represent direction of reaction b. Reactants are to the left of the arrow c. Products are to the right of the arrow Reactant 1 + Reactant 2 Product 1 + Product 2

  3. 5. Symbols are used to represent the phase of matter of each substance a. s – solid b. l – liquid c. g – gas d. aq – water solution 6. Word equations a. Indicate a chemical reaction b. Still use symbols for phase of matter c. carbon (s) and oxygen (g) yield carbon dioxide (g) 7. Skeleton equations a. Uses chemical formulas b. Does not provide other information c. C + O2 -------> CO2

  4. Types of Chemical Reactions A. Types of reactions 1. Synthesis a. Occur when two or more substances combine to form one new substance b. Examples are A + B AB 2 Na(s) + Cl2 (g) 2 NaCl (s) CaO (s) + H2O (l) Ca(OH) 2 (s) 2. Combustion a. Oxygen combines with a substance and releases energy in the form of heat and light b. Examples are C(s) + O2 (g) CO2 (g) is the burning of coal CH4 (g) + 2O2 (g) CO2 (g) +2 H2O (g)

  5. 3. Decomposition a. One substance breaks down into two or more different substances b. Examples are AB A + B 2 NaN3 (s) 2 Na(s) + 3 N2 (g) 4. Single replacement a. Atoms of one element trade places with another element in a compound b. A + BX  AX + B c. To determine if a single replacement reaction will occur, must use the activity series 1. Lists elements based on their reactivity

  6. c. Examples are A + BX -- AX + B Cu(s) + 2AgNO3(aq) -- 2Ag(s) + Cu(NO)3 (aq) 5. Double replacement a. Exchange of ions between two substances b. Examples are AX + BY -- AY + BX KCl(aq) + HBr (aq) -- KBr (aq) + HCl (aq) c. Guidelines for double displacement reactions 1. Write the skeleton equation with the reactants 2. Identify cations and anions 3. Pair each cation with the anion from the other compound 4. Write the formulas for the products 5. Write the complete reaction 6. Balance the equation

  7. III. Balancing chemical equations Law of conservation of mass must be followed Balance equations by using coefficients (numbers in front of formulas) Rules for balancing equations 1. Write the skeleton equation 2. Count the atoms of the elements in the reactants 3. Count the atoms of the elements in the products 4. Change the coefficients to make the number of atoms of each element the same on both sides 5. Reduce coefficients, if possible 6. Check your work

  8. IV. Reactions in Aqueous Solutions A. Solutions 1. Substance dissolved is a solute 2. Substance dissolving is a solvent 3. An aqueous solution is one in which water is the solvent B. Precipitates 1. Some reactions in aqueous solutions will produce solids (precipitates) 2. Not all ions will combine to form precipitates, some will stay as ions 3. Ionic equations a. Shows all particles in a reaction 2Na+(aq) + 2OH-(aq) + Cu2+(aq) + 2Cl- (aq) --> 2Na+ (aq) + 2 Cl- (aq) + Cu(OH)2 (s) b. Spectator ions do not react and remain separate c. Net ionic equations only show the reaction of the ions combining 2OH-(aq) + Cu2+(aq) -- Cu(OH)2 (s)

  9. Solubility An aqueous solution is one where a solid is dissolved in water Solute is the substance dissolved Solvent is the substance doing the dissolving Rules for solubility in water 1. Most nitrates (NO3-) are soluble. 2. Most salts containing an alkali metal or NH4+ are soluble 3. Most halogens (except F) are soluble - Exceptions are Ag+, Pb2+, and Hg22+ 4. Most sulfates (SO42-) are soluble. 5. Most hydroxides (OH-) are only slightly soluble 6. Most sulfides, carbonates, chromates, and phosphates are slightly soluble. Rules follow this order and there are some exceptions Precipitates are a solid formed when two aqueous solutions react

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