Chapter 10: Chemical Reactions Recall A chemical bond is a force of attraction that holds two atoms together Involves valence electrons Three types of bonds: Metallic (metal + metal) Ionic (metal + nonmetal) transfer electrons Covalent (nonmetal + nonmetal) share electrons Recall Ionic Bonds - Between oppositely charged ions. Transfer of electrons Between metals and non-metals Example - Sodium Chloride (NaCl)Sodium Chloride (NaCl) Cl Na 1- 1+ Recall Covalent Bond Two non-metals share electrons Example Water (H 2 O)Water (H 2 O) OHH Recall Metallic Bond Between positively charged metal ions and the electrons in a metal Many properties of metals, such as conductivity, ductility, and malleability, result from the freely moving electrons in the metal Notice how the electrons do not just stay with one ion Al Physical v. Chemical Changes Physical Changes Change in shape, size, color, or state(phase change) Change without a change in chemical composition Chemical Changes a substance becomes another substance having different properties Physical v. Chemical Change Tearing paper Mixing vinegar & baking soda Soured milk Cutting your hair Burning a piece of wood Water evaporating physical chemical physical A. Chemical Reactions The process by which a chemical change occurs and different substances are formed Atoms are rearranged, and chemical bonds are broken and reformed O2O2 H2H2 B. Indicators of a Chemical Reaction Temperature change Light is produced Explosion occurred Precipitate (solid) formed Color change New odor formed Gas formed C. Chemical Equations Shorthand form for writing what reactants are used and what products are formed in a chemical reaction A + B C + D ReactantsProducts C. Chemical Equations Cont. produces, forms, decomposes, yields +plus, and (s)solid (l)liquid (g)gas (aq)aqueous (solid dissolved in water) D. Components of a Chemical Equation 2H 2 + O 2 2H 2 O Chemical Formulas Chemical Formula Subscripts Subscript Chemical formulas used to identify the substances involved in the reaction. Subscripts tell how many of each atom. D. Components of a Chemical Equation 2H 2 + O 2 2H 2 O Chemical Formulas Chemical Formula Coefficient Coefficients used BEFORE THE FORMULA to tell how many of each compound reacts E. Describing Equations Describing Coefficients: Individual atom = atom Covalent compound = molecule Ionic compound = unit Examples: 3CO 2 = 3 molecules of carbon dioxide 2Mg = 2 atoms of magnesium 4MgO = 4 units of magnesium oxide Practice: Writing Skeletal Equations Two atoms of aluminum react with three units of aqueous copper (II) chloride to produce three atoms of copper and two units of aqueous aluminum chloride. 2Al(s) + 3CuCl 2 (aq) 3Cu(s) + 2AlCl 3 (aq) Practice: Writing Skeletal Reactions 4 NH O 2 4 NO + 6 H 2 O Four molecules of ammonia react with five molecules of oxygen to produce four molecules nitrogen monoxide and six molecules of water Practice: Writing Word Equations 2Fe(s) + 3Cl 2 (g) 2FeCl 3 (s) Two atoms of solid iron react with three molecules of chlorine gas to produce two units of iron(III) chloride F. Law of Conservation of Mass Mass is neither created or destroyed in a chemical reaction The total mass and number of atoms has to stay the same Basis for balancing equations 4 H 2 O 4 H 2 O 2 H 2 + O 2 2H 2 O G. Balancing Equations Same numbers of each type of atom on each side of the equation Al + S Al 2 S 3 Not Balanced 2Al + 3S Al 2 S 3 Balanced H. Steps For Balancing Equations 1. Write the unbalanced equation 2. Count atoms on each side 3. Add coefficients to make numbers of atoms equal on both sides Subscript coefficient=number of atoms (2H 2 O = 4 H) 4. Reduce coefficients to lowest possible ratio, if needed 5. Double check atom count to ensure its balanced I. Hints For Balancing Equations Balance in the following order 1.Polyatomic ions (keep as a single unit if they appear on both sides) 2.Metals 3.Nonmetals 4.Hydrogen 5. Oxygen Tutorial on Balancing Equations Balancing Equation- Example Hydrogen gas and chlorine gas react to form gaseous hydrochloric acid (hydrogen monochloride) H 2 (g) + Cl 2 (g) HCl (g) H Cl Balancing Equation- Example Aluminum and aqueous copper (II) chloride react to form copper and aqueous aluminum chloride Al (s) + CuCl 2 (aq) Cu (s) + AlCl 3 (aq) Al Cu Cl Balancing Equation- Example Aqueous sodium hydroxide and calcium bromide react to form solid calcium hydroxide and aqueous sodium bromide NaOH (aq) + CaBr 2 (aq) Ca(OH) 2 (s) + NaBr (aq) Na OH Ca Br