1. Chapter 11 “Chemical Reactions”

2. Section 11.1 p. 321 Describing Chemical Reactions

3. All chemical reactions…
have two parts:
Reactants = substances you start with
Products = end with
reactants turn into products
Reactants ® Products

4. - Page 321
Products
Reactants

5. In a chem rxn
Atoms not created or destroyed (Law of Conservation of Mass)
rxn described in a:
#1. sentence every item is a word
Copper reacts with chlorine to form copper (II) chloride.
#2. word equation some symbols used
Copper + chlorine ® copper (II) chloride

6. Symbols in equations? – Text page 323
arrow (→) separates reactants from products (points to products)
Read as: “reacts to form” or yields
plus sign = “and”
(s) after formula = solid: Fe(s)
(g) = gas: CO2(g)
(l) = liquid: H2O(l)

7. Symbols used in equations
(aq) after formula = dissolved in water, aqueous solution: NaCl(aq) is salt water solution
­ used after product - indicates gas produced: H2↑
¯ used after product - indicates solid produced: PbI2↓

8. Symbols used in equations
double arrow indicates a reversible reaction (more later)
shows that heat supplied to rxn
indicates catalyst supplied (here, platinum is catalyst)

9. substance that speeds up rxn, w/o being changed or used up in rxn
What is a catalyst?
substance that speeds up rxn, w/o being changed or used up in rxn
Enzymes - biological or protein catalysts in your body

10. #3. The Skeleton Equation
Uses formulas and symbols to describe rxn
but doesn’t indicate how many; means they’re NOT balanced
All chem equations are description of rxn

11. Write a skeleton equation for:
Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas.
Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.

12. Now, read these equations:
Fe(s) + O2(g) ® Fe2O3(s)
Cu(s) + AgNO3(aq) ® Ag(s) + Cu(NO3)2(aq)
NO2(g) N2(g) + O2(g)

13. #4. Balanced Chemical Equations
Atoms can’t be created or destroyed in an ordinary reaction:
All atoms we start with we must end up with (balanced!)
balanced equation has same # of each element on both sides of equation

14. Rules for balancing:
Assemble correct formulas for all reactants and products, using “+” and “→”
Count # of atoms of each type on both sides
Balance elements one at a time by adding coefficients (the numbers in front) where you need more - save balancing the H and O until LAST!
(hint: I prefer to save O until the very last)
Double-Check make sure balanced

15. Never Never change subscript (only change coefficients)
changing subscript (formula) describes different chemical
H2O different than H2O2
Never put coefficient in middle of formula; only in front
2NaCl is okay, but Na2Cl is not.

16. Practice Balancing Examples
_AgNO3 + _Cu ® _Cu(NO3)2 + _Ag
_Mg + _N2 ® _Mg3N2
_P + _O2 ® _P4O10
_Na + _H2O ® _H2 + _NaOH
_CH4 + _O2 ® _CO2 + _H2O 2 2 3 4 5 2 2 2 2 2

17. Balancing Equations Balancing Chemical Reactions
Mark Rosengarten – 8:21

18. Types of Chemical Reactions
Section 11.2 p. 330
Types of Chemical Reactions

19. Types of Reactions 5 major types.
predict the products
predict whether or not they will happen at all
How? We recognize them by their reactants

20. #1 - Combination Reactions
Combine = put together
2 substances combine to make one cmpd (also called “synthesis”)
Ca + O2 ® CaO
SO3 + H2O ® H2SO4
predict products, especially if reactants are 2 elements
Mg + N2 ® _______
Mg3N2 (symbols, charges, cross)

21. Complete and balance: Then balance by changing just coefficients only
Ca + Cl2 ®
Fe + O2 ® (assume iron (II) oxide is the product)
Al + O2 ®
Remember first step…write correct formulas – you can still change subscripts at this point, but not while balancing!
Then balance by changing just coefficients only

22. #1 – Combination Reactions
Additional Notes:
a) Some nonmetal oxides react with H2O - produces acid:
SO2 + H2O  H2SO3
b) Some metallic oxides react with H2O - produces base:
CaO + H2O  Ca(OH)2
(how “acid rain” forms)

23. #2 - Decomposition Reactions
decompose = fall apart
one reactant breaks apart into 2 or more elements or cmpds
NaCl Na + Cl2
CaCO CaO + CO2
Note: energy (heat, sunlight, electricity, etc.) usually required

24. #2 - Decomposition Reactions
predict products if binary cmpd (made of 2 elements)
It breaks apart into the elements:
H2O
HgO

25. #2 - Decomposition Reactions
If cmpd has > 2 elements you must be given one of products
other product from the missing pieces
NiCO CO2 + ___
H2CO3(aq) ® CO2 + ___
heat

26. #3 - Single Replacement Reactions
One element replaces another (new dance partner)
Reactants must be an element & cmpd
Products will be a different element and different cmpd
Na + KCl ® K + NaCl
F2 + LiCl ® LiF + Cl2
(Cations switched)
(Anions switched)

27. #3 Single Replacement Reactions
Metals replace other metals (they can also replace H)
K + AlN ®
Zn + HCl ®
Think of water as: HOH
Metals replace first H, then combines w/ hydroxide (OH).
Na + HOH ®

28. #3 Single Replacement Reactions
can even tell whether or not single replacement rxn will happen:
b/c some chemicals more “active” than others
More active replaces less active
list – p Activity Series of Metals
Higher on list replaces lower

29. The “Activity Series” of Metals
Lithium
Potassium
Calcium
Sodium
Magnesium
Aluminum
Zinc
Chromium
Iron
Nickel
Lead
Hydrogen
Bismuth
Copper
Mercury
Silver
Platinum
Gold
Higher activity
Metals can replace other metals, if they are above metal trying to replace (i.e. Zn will replace Pb)
Metals above H can replace H in acids.
Metals from Na upward can replace hydrogen in H2O
Lower activity

30. The “Activity Series” of Halogens
Higher Activity
Halogens can replace other
halogens in compounds, if they are above halogen they are replacing
Fluorine
Chlorine
Bromine
Iodine
Lower Activity
2NaCl(s) + F2(g) 
2NaF(s) + Cl2(g)
???
MgCl2(s) + Br2(g) 
No Reaction!
???

31. #3 Single Replacement Reactions Practice:
Fe + CuSO4 ®
Pb + KCl ®
Al + HCl ®

32. #4 - Double Replacement Reactions
Two things replace each other.
Reactants must be two ionic compounds, in aqueous solution
NaOH + FeCl3 ®
positive ions change place (dance partners)
NaOH + FeCl3 ® Fe+3 OH- + Na+1 Cl-1
= NaOH + FeCl3 ® Fe(OH)3 + NaCl

33. #4 - Double Replacement Reactions
Have certain “driving forces”, or reasons
only happens if one product:
a) doesn’t dissolve in water & forms solid (a “precipitate”), or
b) is gas that bubbles out, or
c) is molecular compound (usually water)

34. Complete and balance:
assume all of the following reactions actually take place:
CaCl2 + NaOH ®
CuCl2 + K2S ®
KOH + Fe(NO3)3 ®
(NH4)2SO4 + BaF2 ®

35. How to recognize which type?
Look at the reactants:
E + E = Combination
C = Decomposition
E + C = Single replacement
C + C = Double replacement

36. Practice Examples: H2 + O2 ® H2O ® Zn + H2SO4 ® HgO ® KBr + Cl2 ®
AgNO3 + NaCl ®
Mg(OH)2 + H2SO3 ®

37. #5 – Combustion Reactions
Combustion means “add oxygen”
Normally, a cmpd composed of only C, H, (and maybe O) is reacted with oxygen – called “burning”
Complete combustion, products are CO2 and H2O
If incomplete, products are CO (or possibly just C) and H2O

38. Combustion Reaction Examples:
C4H10 + O2 ® (assume complete)
C4H10 + O2 ® (incomplete)
C6H12O6 + O2 ® (complete)
C8H8 + O2 ® (incomplete)

39. SUMMARY: An equation... Describes a rxn
Must be balanced (follows the Law of Conservation of Mass)
only balance by changing coefficients
special symbols to indicate physical state, catalyst or energy required, etc.

40. Reactions
5 major types
We can tell what type they are by looking at reactants
Single Replacement happens based on the Activity Series
Double Replacement happens if one product is: 1) a precipitate (an insoluble solid), 2) water (a molecular compound), or 3) a gas

41. Section 11.3 p. 342 Reactions in Aqueous Solution
KMnO4
Co(NO3)2
NiCl2
CuSO4
K2Cr2O7
K2CrO4

42. Net Ionic Equations
Many reactions occur in water- that is, in aqueous solution
When dissolved in water, many ionic cmpds “dissociate”, or separate, into cations & anions
Now write ionic equation

43. Net Ionic Equations
Example (needs to be a double replacement reaction)
AgNO3 + NaCl  AgCl + NaNO3
1. this is the full balanced equation
2. next, write it as ionic equation by splitting the cmpds into their ions:
Ag1+ + NO31- + Na1+ + Cl1- 
AgCl + Na1+ + NO31-
Note that the AgCl did not ionize, because it is a “precipitate” (Table 11.3 p. 344)

44. Net Ionic Equations
3. simplify by crossing out ions not directly involved (called spectator ions)
Ag1+ + Cl1-  AgCl
This is called the net ionic equation
Let’s talk about precipitates before we do some other examples

45. Predicting the Precipitate
Insoluble salt is a precipitate [note Figure 11.11, p.342 (AgCl)]
General solubility rules are found:
Table 11.3, p. 344 in textbook
Reference section - page R54 (Table B.9)

46. Let’s do some examples together of net ionic equations, starting with these reactants:

47. BaCl2 + AgNO3 →

48. NaCl + Ba(NO3)2 →

49. Pb(NO3)2(aq) + H2SO4(aq) 