Chemical Equations and Reactions

1. Chemical Equations and Reactions Chapter Eight

2. A chemical reaction is a process by which two or more substances are changed into one or more different substances.

3. A chemical equation represents with symbols and formulas, the idenities and relative molar amounts of reactents and products in a chemical reaction.(NH4)2Cr2O7(s) → N2(g) + Cr2O3(s) + 4H2O(g)

4. There is a definite set of clues that a chemical change is taking place:temperature changeevolution of a gasformation of a precipitate (new solid)production of lightproduction of electric currentproduction of soundcolor change

5. An accurate chemical equation must: • Represent facts • Contain correct formulas • Satisfy the Law of Conservation of Mass

6. Before a correct formula equation is written, a word equation must be visualized.

8. Discuss balancing chemical equations.

9. Chemical Reactions Section Two

10. In synthesis reactions, also known as composition reactions, two or more substances combine to form a new compound.A + B → AB

11. Synthesis reactions often involve a combination with oxygen or sulfur.Mg + S → MgS2Fe + O2 → 2FeO

12. Some nonmetals burn in oxygen.C + O2→ CO2

13. The water forming reaction happens with a bang.2H2 + O2→ 2H2O

14. Many metals react actively with halogens.2Na + Cl2→ 2NaCl2K + I2 → 2KIU + 3F2 → UF6(g)

15. Active metals react with water to form hydroxides.2Na + 2HOH → 2NaOH + H2Ca + 2HOH → Ca(OH)2 + H2

16. Certain nonmetallic oxides may react with water to form acids as in the acid rain reaction shown below.SO2 + H2O → H2SO32H2SO3 + O2 → 2H2SO4

17. Decomposition Reactions

18. In a decomposition reaction, a single compound undergoes a reaction that produces two or more simpler substances.AX → A + X

19. Binary compounds may decompose.2HgO(s)→ 2Hg + O2↑2H2O → 2H2 + O2 Electricity

20. Metallic carbonates decompose to form carbon dioxide and a metallic oxide.CaCO3→ CaO + CO2

21. Metallic hydroxides decompose into a metallic oxide and water.Ca(OH)2→ CaO + H2O

22. Metallic chlorates decompose into a chloride and oxygen.2NaClO3 → 2NaCl + 3O2

23. Oxyacids decompose into nonmetallic oxides and water.H2CO3 → CO2 + H2O

24. Single Displacement Reactions

25. In a single displacement (replacement) reaction one element replaces a similar element in a compound.AB + C → AC + B

26. A more active metal may replace a less active metal in a compound.Fe + CuSO4 → FeSO4 + Cu

27. Active metals may replace the hydrogen in water.2Na + H2O → 2NaOH + H2

28. Less active metals may react with steam to form metallic oxides and hydrogen.3Fe + 4H2O → Fe3O4 + 4H2

29. More active metals react with acids to release hydrogen.2HCl + Mg → MgCl2 + H2

30. A more active halogen may replace a less active halogen.Cl2 + 2KBr → 2KCl + Br2

31. Double Replacement Reactions

32. In a double replacement reaction, two compounds in aqueous solution exchange components to form two new compounds with one usually being a precipitate.AgNO3 + NaCl → NaNO3 + AgCl↓

33. Combustion Reactions

34. In combustion, a fuel, usually a hydrocarbon, combines with oxygen in the air to release heat and light.C3H8 + 5O2 → 3CO2 + 4H2O

35. The activity series is a list of elements that have been arranged according to their ease of reacting. It is especially helpful in replacement reactions.