1. Unit 9
Chemical Reactions

2. 9.1 Chemical Reactions & Equations
Chemical reaction - The process by which the atoms of one or more substances are rearranged to form different substances
Occur when substances go through a chemical changes

3. Evidence of a chemical reaction
Temperature changes
Color change
Odor
Gas bubbles
Formation of a solid (precipitate)

4. Representing Chemical Reactions
Reactants and Products
NaHCO3 + HC2H3O2  CO2 + H20 + NaC2H3O2

5. Symbol Purpose Separates two or more reactants or products
Seperates reactants from products
Separates reactants from products and indicates a reversible reactions
Solid state
Liquid state
Gas state
Water solution (aqueous state)

6. Word Equations
Solid aluminum and liquid bromine yield solid aluminum bromide.
Solid calcium carbonate and aqueous hydrochloric acid yield aqueous calcium chloride, liquid water, and gaseous carbon dioxide.

7. Write the Word Equation
Zn(s) + HCl (aq)  ZnCl2(aq) + H2(g)
NH3(g) + O2(g)  NO2(g) + H2O (l)

8. Chemical Equations Law of Conservation of Mass =
Chemical equation – statement that uses chemical formulas to show the identities and relative amounts of substances involved in a chemical reaction

9. Balancing Chemical Equations
Law of Conservation of Mass: mass of reactants must = mass of products
If I start with 12 g of Carbon I have to end with 12 g of Carbon
Each side of the equations must contain the same number (mass) of atoms

10. Balance using COEFFICIENTS – number written in front of a reactant or product
Usually whole numbers
Not written if the value is ne
Show the lowest whole number ratio of the amounts of all the reactants and products

11. Never ever ever ever ever change the chemical formulas!!! Correct:
2H2 + O2  2H2O
Incorrect:
H2 + O2  H2O2

12. How to balance
Determine the number of atoms of each element on reactants and products side.
Balance elements one at a time with coefficients.
Make sure the number of atoms on each side of the equation are equal.
Put coefficients in lowest whole number ratio.

13. Mg + O2  MgO Cu(SO4) + Al  Al2(SO4)3 + Cu

14. Challenge!
C2H O  CO2 + H2O

15. Write the equation and balance
In water, Iron (III) chloride reacts with sodium hydroxide producing solid iron (III) hydroxide and sodium chloride.

16. 9.2 Classifying Chemical Reactions
There are 5 main types of reactions, classified according to what happens in them:
Synthesis
Decomposition
Combustion
Single Replacement
Double Replacement

17. Synthesis Reactions 2 or more reactants join to form a single product
H2(g) + O2(g)  H2O(l)
CaO(s) H2O(l)  Ca(OH)2(s)

18. Decomposition Reaction
A single reactant breaks apart
H2O(l)  H2(g) + O2(g)
Aluminum oxide decomposes when electricity is passed through it

19. Combustion Occurs when one of the reactants is oxygen
CH4(g)+ O2(g) CO2(g) + H2O(l)
SO2 + O2  SO3

20. Single Replacement Reactions
One element replaces the atoms of another element in a compound
CuCl2(aq) + Al(s)  AlCl3(aq)+ Cu(s)

21. Activity Series An element will replace another
element only if it is BELOW it!
Na + AlCl3
Cu + ZnCl2
Br2 + NaF

22. Double Replacement Reactions
Involves an exchange of ions between two compounds
Pb(NO3)2(aq) + 2KI(aq)  PbI2(s)+ 2K(NO3)(aq)
NaCl(aq) + Ag(NO3)(aq)  AgCl(s) + NaNO3 (aq)

23. A solid produced in a double replacement reaction is called a precipitate
What are the precipitates from the previous reactions?

24. Double replacement reactions will produce either water, a precipitate, or a gas
Predict the products:
NaOH + CuCl2 

25. Predicting Products of Chemical Reactions
Decide what type of reaction you have
Predict products
Balance reaction

26. Li Cl2 
HgO 

27. K CaO 
H KCl 
Pb(NO3) KI 

28. 9.3 Reactions in Aqueous Solutions
Double replacement reactions occur between substances in aqueous solutions and produce precipitates, water, or gases
Aqueous solution contains one or more solutes dissolved in water (the solute)

29. When ionic compounds dissolve in water their ions separate (dissociation)
NaCl

30. Types of Reactions in Aqueous Solutions
Reactions that form precipitates:
2NaOH(aq) + CuCl2 (aq)  2NaCl(aq) + Cu(OH)2 (s)
Does not show detail of what is happening in the reaction

31. Ionic equations
Substances that are in aqueous solution are written as ions
Write the previous chemical equation as an ionic equation

32. Complete ionic equation shows all the particles in a solution
Net ionic equations show only the ions that take part in the reaction
Atoms that are ions on both sides of the reaction do not participate in the reaction (spectator ions)

33. 2NaOH(aq) + CuCl2 (aq)  2NaCl(aq) + Cu(OH)2(s)
Complete ionic equation
Net ionic equation

34. Ba(NO3)2(aq) + Na2CO3  BaCO3(s) + 2NaNO3(aq)
Complete ionic equation:
Net ionic equation:

35. Reactions that form water
HBr(aq) + NaOH(aq)  H2O(l) + NaBr(aq)
Complete ionic equation
Net ionic equation

36. Reactions that form gasses
2HI(aq) + Li2S(aq)  H2S(g) + 2LiI(aq)
Complete ionic equation
Net ionic equation