11 18 how are equations balanced part ii

Launch: 11/18   Grab your binder and immediately take a seat!

  Place homework (practice questions) on desk.

Balance the following equations showing all 3-steps in your work!

1.  __Na + __Cl2 __NaCl

2.  __CH4 + __O2 __CO2 + __H2

Announcements   Quiz on Friday!

  and every Friday until Winter Break

How are equations balanced? – Part II

Mr. Heffner 11/18/09

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,

N2 + H2 NH3

  Step #1: Count the atoms on both sides

N2 + H2 NH3

Example #1

2 X N 2 X H 1 X N 3 X H

Unbalanced!

  Step #2: Change coefficient & multiply out

N2 + H2 NH3

Example #1

2 X N 2 X H 1 X N 3 X H

2

2 X N 6 X H

2X( )

  Step #3: Check tally (and repeat)

N2 + H2 NH3

Example #1

2 X N 2 X H

2

2 X N 6 X H

3

6 X H

Still unbalanced!

3X( )

  Step #3: Check tally (and repeat)

N2 + H2 NH3

Example #1

6 X H

2

2 X N 6 X H

3

2 X N

Balanced!

Balancing Buffet   Grab a menu and “order” your 100 point “dinner”

  Appetizers = 5 points   Entrees = 10 points

  Desserts = 15 points

  Write questions on a piece of binder paper

  Balance the equation showing all of your work! 1.  Count the atoms 2.  Add a coefficient 3.  Check tally (and repeat)

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