1. Section 2.6—Chemical Reactions
If we’re going to do chemical reactions with antacids, we’d better know how to write them!

2. Watch as 2 H2 and 1 O2 undergo a chemical reaction
Chemical Reactions
Bonds are broken. New bonds are made to form new compounds.
2 H2 + O2  2 H2O O H H
Watch as 2 H2 and 1 O2 undergo a chemical reaction

3. Chemical Reactions
Bonds are broken. New bonds are made to form new compounds.
2 H2 + O2  2 H2O H O O H O H
The compounds in the end are different from those in the beginning H
Bonds are broken and formed between different atoms

4. Chemical Equations What is a Chemical Equation??
A shorthand method of showing how reactants convert to products

5. Examples of Chemical Equations
Word equation: magnesium metal is reacted with aqueous hydrochloric acid to produce aqueous magnesium chloride and hydrogen gas 
Formula equation: Mg (s) + 2 HCl (aq) MgCl2 (aq) + H2 (g)
Visualization

6. Parts of a Chemical Equation
The starting materials for the reaction—each compound is separated by a “+”
Formed in the reaction
Reactants
Products
NaCl (aq) + AgNO3 (aq)  AgCl(s) + NaNO3 (aq)
States of matter
Arrow
s = solid
l = liquid
g = gas
aq = aqueous (dissolved in water)
Read as:
Yields
Produces
Forms
Makes
etc.

7. Special Note about Diatomics
Lets break the word down Di= two atomic=atoms
Diatomics are elements that exist naturally as two atoms bonded together
There are seven of them: H2 N2 O2 F2
Cl2
Br2 I2

8. Point to Hydrogen then go to N (#7) and draw a “7”
I Never Bring Classwork Home On Fridays 
I Have No Bright Or Clever Friends
HOBrFINCl - Its pronounced “hober-finkle”

9. Double Replacement Reactions
The cations from two compounds replace each other.
NaCl + AgNO3  AgCl + NaNO3 Cl Ag Cl Na Ag O N Na O N
Two ionic compounds switch ions

10. Double Replacement Reactions
General format of a double replacement reaction:

11. Write the word equation into symbol form
Let’s Practice #1
Aqueous solutions of Copper (II) nitrate and sodium hydroxide form solid copper (II) hydroxide and aqueous sodium nitrate
Example:
Write the word equation into symbol form

12. Write the word equation into symbol form
Let’s Practice #1
Aqueous solutions of Copper (II) nitrate and sodium hydroxide form solid copper (II) hydroxide and aqueous sodium nitrate
Example:
Write the word equation into symbol form
Cu(NO3)2(aq) + NaOH(aq)  Cu(OH)2(aq) + NaNO3(aq)

13. Products of a Double Replacement1
Combine the cation of the first reactant with the anion of the second reactant Ca
Cl2 + Ag
NO3

14. Products of a Double Replacement2
Combine the cation of the second reactant with the anion of the first reactant Ca
Cl2 + Ag
NO3

15. Products of a Double Replacement3
Remember to write cations first …
& balance charges with subscripts when writing formulas
Only leave subscripts that are in the original compound there if they are a part of a polyatomic ion! Ca
Cl2 + Ag
NO3 Ca
Cl2 + Ag
NO3
Ca(NO3)2 +
AgCl

16. Neutralization Reactions
General format of a neutralization reaction:
salt
Water
Neutralization reactions are double replacement reactions where one cation is “H” and one anion is “OH” and water is formed. The other compound formed will be a salt.

17. Products of a Neutralization Reaction1
Combine the cation of the first reactant with the anion of the second reactant H2
SO4 + Na OH

18. Products of a Neutralization Reaction2
Combine the cation of the second reactant with the anion of the first reactant H2
SO4 + Na OH

19. Products of a Neutralization Reaction3
Remember to write cations first …
& balance charges with subscripts when writing formulas
Only leave subscripts that are in the original compound there if they are a part of a polyatomic ion! H2
SO4 + Na OH H2
SO4 + Na OH
Na2SO4 +
HOH
You can write the water as “HOH” when you combine the cation & anion or you can change it to “H2O”

20. Write the products for this reaction
Let’s Practice #2
Example:
Write the products for this reaction
Sr(OH)2 + HBr 

21. Write the products for this reaction
Let’s Practice #2
Example:
Write the products for this reaction
Sr(OH)2 + HBr 
SrBr2 + HOH

22. Write the products for this reaction
Let’s Practice #3
Example:
Write the products for this reaction
H2SO4 + Ca(OH)2 

23. Write the products for this reaction
Let’s Practice #3
Example:
Write the products for this reaction
H2SO4 + Ca(OH)2 HOH + CaSO4

24. Section 2.7—Balancing Equations
We need to finish writing those equations we started!

25. Watch as 2 H2 and 1 O2 undergo a chemical reaction
Chemical Reactions
Bonds and atoms are rearranged to form new compounds.
2 H2 + O2  2 H2O O H H
Watch as 2 H2 and 1 O2 undergo a chemical reaction

26. Chemical Reactions
Bonds and atoms are rearranged to form new compounds.
2 H2 + O2  2 H2O H O O H O H
The compounds in the end are different from those in the beginning H
Bonds are broken and formed between different atoms

27. Law of Conservation of Matter/Mass
Law of Conservation of Matter – Matter cannot be created nor destroyed during chemical or physical changes
Also called the Law of Conservation of Mass (since all matter has mass)

30. How Does the Law Lead to Balancing?
We have to have the same number and types of atoms on each side of the reaction!
We CAN’T lose atoms as we move from reactant to product!!

31. How do we Balance Equations
How do we Balance Equations? Let’s start with discussing what the numbers mean!!
Number of compounds in the reaction
Coefficients
2 H2 + O2  2 H2O
Subscripts
# of atoms in a compound
Subscripts balance charges within a compound.
Coefficients balance atoms in an equation

32. What do Coefficients Really Mean?
CH4 + 2 O2  CO2 + 2 H2O
Total:
1 C
4 H
4 O
Total:
1 C
4 H
4 O
The equation is balanced.

33. How to Balance Chemical Equations

34. How to Balance By Inspection:1
Make a table of elements
_____ C H4 +
_____ O2 
_____ H2 O +
_____ C O2
Reactants
Products C H O

35. How to Balance By Inspection:2
Count the number of each element or ion on the reactants and products side.
Don’t forget to add all the atoms of the same element together—even if it appears in more than one compound!
_____ C H4 +
_____ O2 
_____ H2 O +
_____ C O2
Reactants
Products C 1 1 H 4 2 O 2 3

36. How to Balance By Inspection:3
Add coefficients to balance the numbers
Each time you add a coefficient, update your table with the new quantities of each atom.
_____ C H4 +
_____ 2 O2 
_____ 2 H2 O +
_____ C O2
Reactants
Products C 1 1 H 4 2 4 O 2 4 3 4

37. Tips to Balancing How do you know what order to balance in?
Start With: Elements that appear only 1 time per side
Save for later
Elements that are uncombined
Pb + PbO2 + H+  Pb2+ + H2O
Start With: Elements in most complicated molecules
Save for later
Elements that appear more than 1 time per side
To balance this equation, use the order: O, H, Pb

38. Polyatomic Ions and the balanced equation
Polyatomic ion – Group of atoms that together has a net charge
e.g Nitrate NO31-
Carbonate CO32-
A polyatomic ion is a group of atoms that together have a charge.

39. Balancing with Polyatomic Ions:1
Make a table of elements
You may leave polyatomic ions together—IF they appear intact on both sides of the reaction.
OH-1 is a polyatomic ion that is sometimes “hidden” in H2O.
Re-write H2O as HOH to “see” the OH polyatomic ion. H OH
_____ H3
PO4 +
_____ Ca
(OH)2 
_____
Ca3
(PO4)2 +
_____ H2 O
Reactants
Products H
PO4 Ca OH

40. Balancing with Polyatomic Ions:
Count the number of each element or ion on the reactants and products side. 2 H OH
_____ H3
PO4 +
_____ Ca
(OH)2 
_____
Ca3
(PO4)2 +
_____ H2 O
Reactants
Products H 3 1
PO4 1 2 Ca 1 3 OH 2 1

41. Balancing with Polyatomic Ions:3
Add coefficients to balance the numbers H OH
_____ 2 H3
PO4 +
_____ 3 Ca
(OH)2 
_____
Ca3
(PO4)2 +
_____ 6 H2 O
Reactants
Products H 3 6 1 6
PO4 1 2 2 Ca 1 3 3 OH 2 6 1 6

42. Balance the following equation
Let’s Practice #1
Example:
Balance the following equation
__ HCl + __ Ca(OH)2  __ CaCl2 + __ H2O

43. Balance the following equation
Let’s Practice #1
Example:
Balance the following equation
Did you see the “OH” polyatomic ion? Should we change H2O to HOH? 2 1 1 2
__ HCl + __ Ca(OH)2  __ CaCl2 + __ H2O
HOH

44. Balance the following equation
Let’s Practice #2
Example:
Balance the following equation
__ H2 + __ O2  __ H2O

45. Balance the following equation
Let’s Practice #2
Example:
Balance the following equation 2 1 2
__ H2 + __ O2  __ H2O

46. Balance the following equation
Let’s Practice #3
Example:
Balance the following equation
__ Fe + __ O2  ___ Fe2O3

47. Balance the following equation
Let’s Practice #3
Example:
Balance the following equation 4 3 2
__ Fe + __ O2  ___ Fe2O3