1. IIIIIIIVV I.Intro to Reactions Ch.7– Chemical Reactions

2. A.Signs of a Chemical Reaction n heat and light produced n Formation of a gas n Formation of a precipitate n Color change

3. B.Law of Conservation of Mass n mass is neither created nor destroyed in a chemical reaction 4 H 2 O 4 H 2 O 4 g32 g 36 g n total mass stays the same n atoms can only rearrange

4. C. Chemical Equations A+B  C+D REACTANTSPRODUCTS

5. p. 246 C. Chemical Equations

6. D. Writing Equations n Identify the substances involved. n Use symbols to show: 2H 2 (g) + O 2 (g)  2H 2 O(g)  How many? - coefficient  Of what? - chemical formula  In what state? - physical state n Remember the diatomic elements.

7. Example: 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. How many? Of what? In what state? Al 2(s)(s)+ 3CuCl 2 (aq)  3 Cu(s)(s)+ 2AlCl 3 (aq)

8. E. Describing Equations n Describing Coefficients:  individual atom = “atom”  covalent substance = “molecule”  ionic substance = “unit” 3 molecules of carbon dioxide 2 atoms of magnesium 4 units of magnesium oxide 3CO 2  2Mg  4MgO 

9. Example to produce How many? Of what? In what state? Zn(s) + 2HCl(aq)  ZnCl 2 (aq) + H 2 (g) One atom of solid zinc reacts with two molecules of aqueous hydrochloric acid one unit of aqueous zinc chlorideand one molecule of hydrogen gas.

10. IIIIIIIVV II. Balancing Equations Chemical Reactions

11. A. Balancing Steps 1.Write the unbalanced equation. 2.Count atoms on each side. 3.Add coefficients to make #s equal. Coefficient  subscript = # of atoms 4.Reduce coefficients to lowest possible ratio, if necessary. 5.Check yourself before you wreck yourself

12. B. Helpful Tips n one element at a time. n Update ALL atom counts after adding a coefficient. n If an element appears more than once per side, balance it last.

13. Al + CuCl 2  Cu + AlCl 3 Al Cu Cl 1 1 1 1 2 3 2  3  6   3 33 2 C. Balancing Example Aluminum and copper(II) chloride react to form copper and aluminum chloride. 2  2  6

14. IIIIIIIVV Chemical Reactions III. Types of Chemical Reactions

15. A. Combustion CH 4 (g) + 2O 2 (g)  CO 2 (g) + 2H 2 O(g) n the burning of any substance in O 2 to produce heat A + O 2  B

16. Na(s)+ O 2 (g)  C 3 H 8 (g)+ O 2 (g)  5 3 4 n Products:  contain oxygen  hydrocarbons form CO 2 + H 2 O CO 2 (g)+ H 2 O(g) Na 2 O(s) 4 2

17. B. Synthesis n the combination of 2 or more substances to form a compound n only one product A + B  AB

18. H 2 (g) + Cl 2 (g)  2 HCl(g)

19. Al(s)+ Cl 2 (g)  AlCl 3 (s) 2 3 2 n Products:  ionic – cross charges  covalent - hard to tell

20. C. Decomposition n a compound breaks down into 2 or more simpler substances n only one reactant AB  A + B

21. 2 H 2 O(l)  2 H 2 (g) + O 2 (g)

22. KBr(l)  K(s) + Br 2 (l) 2 2 n Products:  binary - break into elements  others - hard to tell

23. D. Single Replacement n one element replaces another in a compound  metal replaces metal (+)  nonmetal replaces nonmetal (-) A + BC  B + AC

24. Cu(s) + 2AgNO 3 (aq)  Cu(NO 3 ) 2 (aq) + 2Ag(s)

25. Fe(s)+ CuSO 4 (aq)  Cu(s)+ FeSO 4 (aq) n Products:  metal  metal (+)  nonmetal  nonmetal (-)  free element must be more active (check activity series) Br 2 (l)+ NaCl(aq)  N.R.

26. AB + CD  AD + CB E. Double Replacement n ions in two compounds “change partners” n cation of one compound combines with anion of the other

27. Pb(NO 3 ) 2 (aq) + K 2 CrO 4 (aq)  PbCrO 4 (s) + 2KNO 3 (aq)

28. Pb(NO 3 ) 2 (aq)+ KI(aq)  PbI 2 (s)+ KNO 3 (aq) n Products:  switch negative ions  one product must be insoluble (check solubility table) NaNO 3 (aq)+ KI(aq)  N.R. 2 2