12 14 Balancing Review

Launch: 12/14   Grab your binder and immediately take a seat!

  Place binder paper and a pen/pencil on your desk.

Review Objective #1: I can write balanced chemical equations.

Tonight’s HW: Finish Review Worksheet #1

Launch 12/14

Launch 12/14 16. How many grams does 2 moles of soda niter

NaNO3 weigh? a.  17g b.  85g c.  170g

d.  1700g

Launch Answers

Launch Answers 16. How many grams does 2 moles of soda niter

NaNO3 weigh? a.  17g b.  85g c.  170g

d.  1700g

Practice Exam Results: B1   Our goal = 80%

  Our average = 86%

  Questions dropped   5, 6, 7, 9, 14

Practice Exam Results: B1   Our goal = 80%

  Our average = 78%

  Questions dropped   5, 6, 7, 9, 14

Practice Exam Results: B1   Our goal = 80%

  Our average = 87%

  Questions dropped   5, 6, 7, 9, 14

Practice Exam Results: B1   Our goal = 80%

  Our average = 88%

  Questions dropped   5, 6, 7, 9, 14

Announcements   Unit #5 Exam on Thursday

  3 days to review   Ask questions!

  No copying HW or classwork!

  Make-up work is due on Wednesday

  Binder check this week

Exam Information   30 multiple-choice questions

  Balancing equations (6 questions = 20%)   The mole (9 questions = 30%)

  Conversions (15 questions = 50%)   gram mole (6 questions)

  gram atoms (3 questions)

  gram gram (6 questions)

  3 free response

Review: Balancing Equations

Mr. Heffner 12/14/09

CH4 + 2O2 CO2 + 2H2O

What’s a chemical equation?

Reactants Products “turn into”

What’s a chemical equation?

4Fe2(CO3)3

  Multiply!   8 X Fe

  12 X C   36 X O

Coefficient Subscript

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)

Rule: You can’t change the subscripts!

Example   Balance the equation,

N2 + H2 NH3

  Step #1: Count the atoms on both sides

N2 + H2 NH3

Example

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

Unbalanced!

  Step #2: Change coefficient & multiply out

N2 + H2 NH3

Example

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

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

6 X H

2

2 X N 6 X H

3

2 X N

Balanced!

Snowman Challenge   Directions:

  Send one group member to pick a card   Write down the equation and #

  Balance it showing all work (count, coefficient, check)   When finished, send one group member to have me

check your answer

  Rules:   If you pick it, solve it   Only one card at a time   Show your work!

  Work together

Exit Slip HC2H3O2 + NaHCO3 NaC2H3O2 + H2CO3

1.  Which of the following correctly identifies all of the reactants in the above chemical equation.

a.  NaC2H3O2

b.  NaHCO3 c.  NaC2H3O2 and HC2H3O2 d.  HC2H3O2 and NaHCO3

Exit Slip 2.  How many C atoms are there in 3C2H4?

a.  2 b.  3

c.  5 d.  6

Exit Slip H2 + Cl2 HCl

3.  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 on both sides of the equation.

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 4.  Which of the following is a balanced equation for

the combustion of ethanol (C2H6O)? a.  C2H5OH + 3O2 CO2 + 2H2O b.  C2H5OH + 3O2 2CO2 + 3H2O c.  C2H5OH + O2 2CO2 + 3H2O

d.  C2H5OH + 2O2 3CO2 + 2H2O

Exit Slip __C2H2 + __H2 __CH4

5.  When the equation above is completely balanced, the coefficient for H2 would be

a.  1

b.  2

c.  3

d.  4

Homework   Finish practice questions worksheet