Intro to Reactions

1
Intro to Reactions

• Chemical Reactions

1. Turn in Section 11.1 to your class tray.
2. Get out paper for notes.

2
Why are Chemical Reactions Important?

• Chemical reactions occur everywhere.
• Your body is a chemical machine, if chemical
  reactions did not occur, we would not be alive.

3
A.Signs of a Chemical Reaction

• Evolution of heat and light
• Formation of a gas
• Formation of a precipitate
• Color change

4
B.Law of Conservation of Mass

• mass is neither created nor destroyed in a
  chemical reaction

• total mass stays the same

• atoms can only rearrange

4 H 2 O
4 H 2 O
36 g
4 g
32 g
5
C. Chemical Equations

• AB ? CD

REACTANTS
PRODUCTS
6
C. Chemical Equations
7
D. Writing Equations
2H2(g) O2(g) ? 2H2O(g)

• Identify the substances involved.
• Use symbols to show

• How many? - coefficient

• Of what? - chemical formula

• In what state? - physical state

• Remember the diatomic elements.

8
D. Writing Equations

• Two atoms of aluminum react with three units of
  aqueous copper(II) chloride to produce three
  atoms of copper and two units of aqueous aluminum
  chloride.

• How many?
• Of what?
• In what state?

? 3
Al
2
(s)
3
CuCl2
(aq)
Cu
(s)
2
AlCl3
(aq)
9
E. Describing Equations
Zn(s) 2HCl(aq) ? ZnCl2(aq) H2(g)

• How many?
• Of what?
• In what state?

One atom of solid zinc
reacts with
two molecules of aqueous hydrochloric acid

• to produce

one unit
of aqueous zinc chloride
and one
molecule of hydrogen gas.
10
II. Balancing Equations

• Ch. 11 Chemical Reactions

Get out your notes from yesterday and your
practice sheet
11
Counting Atoms

• How many atoms of each element are in the
  following molecules?
• 1. H2SO4
• 2. Ca(OH)2
• 3. NaCl
• 4. (NH3)3P04
• 5. 3H2O
• 6. 4Al2(CO3)3

12
B. Helpful Tips

• Balance one element at a time.
• Update ALL atom counts after adding a
  coefficient.
• If an element appears more than once per side,
  balance it last.
• Balance polyatomic ions as single units.
• 1 SO4 instead of 1 S and 4 O

13
C. Balancing Example

• Aluminum and copper(II) chloride react to form
  copper and aluminum chloride.

3
3
2
2
1 1 1 1 2
3
2 ?
? 2 ? 6
3 ? 6 ?
? 3