Launch: 11/17   Grab your binder and immediately take a seat!

  Place homework (practice questions) on desk.

Mg + 2H2O Mg(OH)2 + 2H2

3.  Is the above equation balanced? a.  No, because the number of H atoms is not equal

b.  No, because the number of O atoms is not equal c.  Yes, because the number of Mg atoms is not equal

d.  Yes, because there are equal numbers of atoms on both sides of the equation

Launch 11/17 4.  Hydrogen gas (H2) and oxygen gas (O2) react to

form water (H2O). Which of these represents a properly balanced equation for this reaction?

a.  H2 + O2 H2O

b.  2H2 + 2O2 2H2O

c.  2H2 + O2 2H2O

d.  H2 + 2O2 2H2O

Announcements   Unit #5: Chemical Reactions & Stoichiometry

  Class points end next week   Get your HW done   Be respectful

  Quiz on Friday!

How are equations balanced?

Mr. Heffner 11/17/09

  Is the below equation balanced?

Cl2 + H2 2HCl

Review

2 X Cl 2 X H 2 X H 2 X Cl

Multiply the coefficients and

subscripts Yes, it is balanced!

How are equations balanced?   There is a 3-step process for balancing

equations:

1.  Count the atoms on both sides

2.  Change a coefficient & multiply out

3.  Check tally (and repeat)

Only one rule: you can’t change the subscripts

Example #1   Balance the equation,

H2 + O2 H2O

  Step #1: Count the atoms on both sides

H2 + O2 H2O

Example #1

2 X H 2 X O 2 X H 1 X O

Put it underneath Unbalanced!

  Step #2: Change coefficient & multiply out

H2 + O2 H2O

Example #1

2 X H 2 X O 2 X H 1 X O

2

2X( ) 4 X H 2 X O

  Step #3: Check tally (and repeat)

H2 + O2 H2O

Example #1

2 X H 2 X O

2

4 X H 2 X O

2

4 X H

2X( )

Still unbalanced!

  Step #3: Check tally (and repeat)

H2 + O2 H2O

Example #1

2 X O

2

4 X H 2 X O

2

4 X H

Balanced!

Activity   Make the equation on your whiteboard

  Balance the equation with the 3-step method 1.  Count the atoms 2.  Add a coefficient 3.  Check tally (and repeat)

  Raise hand to get checked off

  Record reactants, products, and final balanced equation on worksheet

Practice Questions   Practice question handouts

Exit Slip 1.  In a balanced equation

a.  the reactant atoms are destroyed to make the products

b.  the number of atoms on the reactants side of the equation is equal to the number of atoms on the products

c.  the number of atoms on the reactants side of the equation is not equal to the number of atoms on the products

d.  all compounds have a coefficient of at least 2

Exit Slip H2 + Cl2 HCl

2.  Is the above equation balanced? a.  No, because H2 has a coefficient of 2.

b.  No, because the number of Cl and H atoms are not equal.

c.  Yes, because the number of H atoms is not equal on both sides.

d.  Yes, because there are equal numbers of atoms on both sides of the equation.

Exit Slip 4K + O2 2K2O

3.  In the already balanced reaction above, what is the coefficient for O2?

a.  0 b.  1

c.  2 d.  4

Exit Slip __C + __Br2 __CBr4

4.  When the equation above is completely balanced, the coefficient for Br2 would be

a.  0

b.  1

c.  2

d.  4

Exit Slip __Na + __H2O __NaOH + __H2

5.  When the above equation is completely balanced, the coefficient for NaOH would be

a.  1.

b.  2. c.  4.

d.  8.

Homework   Finish practice question worksheet