1. Section 2.6—Chemical Reactions
Objectives:
Define the components of a chemical reaction
Convert word equations to formula equations
Define and predict products for double replacement and neutralization reactions

2. Watch as 2 H2 and 1 O2 undergo a chemical reaction
Chemical Reactions
When substances react, bonds are broken, atoms are rearranged, and bond are re-formed to create 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 and atoms are rearranged to form new compounds.
2 H2 + O2  2 H2O H O O H O H
The substances in the end are different from those in the beginning. H
Bonds are broken and re-formed between different atoms

4. Chemical Reactions
In chemistry, the “sentence” (showing the starting materials and the final products of a chemical reaction) is called a chemical equation.

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. Writing Chemical Equations
You must write each chemical formula correctly first! (Recall how to write formulas from names - Section 2.2)
“and”, “is mixed with” or “reacts with” = +
“yield”, “produces” and “forms” = 
Then after they are written, chemical equations have to be balanced – we’ll do that in Sec. 2.7!

8. Write the word equation into symbol form
Let’s Practice #1
Aluminum metal is reacted with hydrochloric acid to form aluminum chloride and hydrogen gas
Example:
Write the word equation into symbol form

9. Write the word equation into symbol form
Let’s Practice #1
Aluminum metal is reacted with hydrochloric acid to form aluminum chloride and hydrogen gas
Example:
Write the word equation into symbol form
Al + HCl  AlCl3 + H2

10. Write the word equation into symbol form
Let’s Practice #2
Copper (II) nitrate and sodium hydroxide form copper (II) hydroxide and sodium nitrate
Example:
Write the word equation into symbol form

11. Write the word equation into symbol form
Let’s Practice #2
Copper (II) nitrate and sodium hydroxide form copper (II) hydroxide and sodium nitrate
Example:
Write the word equation into symbol form
Cu(NO3)2 + NaOH  Cu(OH)2 + NaNO3

12. 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

13. Double Replacement Reactions
The general format of a double replacement reaction:

14. Products of a Double Replacement1
Combine the cation of the first reactant with the anion of the second reactant
CaCl2 + AgNO3 

15. Products of a Double Replacement2
Combine the cation of the second reactant with the anion of the first reactant
CaCl2 + AgNO3 

16. Products of a Double Replacement
Remember to write cations first … 3
& balance charges with subscripts when
writing formulas
Remember NOT the change the subscripts that are part of any polyatomic ion! Ca
Cl2 + Ag
NO3 Ca
Cl2 + Ag
NO3
Ca(NO3)2 +
AgCl

17. Neutralization Reactions
Neutralization reactions are double replacement reactions where one cation is “H” and one anion is “OH” and water is formed.
General format of a neutralization reaction:
ACID BASE IONIC WATER
COMPOUND

18. Products of a Neutralization Reaction
Combine the cation of the first reactant (the acid) with the anion of the second reactant (the base). This gives you the water. 1
H2SO4 + NaOH 

19. Products of a Neutralization Reaction2
Combine the cation of the second reactant with the anion of the first reactant. This gives you an ionic compound.
H2SO4 + NaOH 

20. 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”

21. Write the products for this reaction
Let’s Practice #3
Example:
Write the products for this reaction
Sr(OH)2 + HBr 

22. Write the products for this reaction
Let’s Practice #3
Example:
Write the products for this reaction
Sr(OH)2 + HBr 
SrBr2 + HOH

23. Write the products for this reaction
Let’s Practice #4
Example:
Write the products for this reaction
HCl + Ca(OH)2 

24. Write the products for this reaction
Let’s Practice #4
Example:
Write the products for this reaction
HCl + Ca(OH)2 
CaCl2 + HOH