CHEMICAL REACTIONS Part 3 by Jim Alton

1
CHEMICAL REACTIONSPart 3by Jim Alton

• Wed Thurs
• Pg 24 to pg 31

2
Sources

• Frank, David Little, John Miller, Steve (2000).
  Science Explorer - Chemical Interactions.
  Needham, MA Upper Saddle River, NJ
• Hurd,, Dean Silver, Myrna Bacher, Angela
  (1993). Physical Science. Needham, MA Englewood
  Cliffs,NJ Prentice Hall.
• Sibert, Gwen (5/16/2004). Types of Equations.
  Retrieved November 23, 2006, from Types of
  Equations Web site http//www.chem.vt.edu/RVGS/AC
  T/notes/Types_of_Equations.html
• Hand (2006). Mr. Hands 8th Grade Science Site,
  Retrieved November 23, 2006, from Mansfield
  Middle School Web Site
• http//www.mansfieldct.org/schools/mms/index.htm
• Quotes by Stephen Wright
• NJCCCS 5.1, 5.6

3
Objectives

• Describe info conveyed in a chemical reaction
• Identify and describe 3 categories of chemical
  reactions

4
Describing Chemical Reactions

• Formulas show chemistry at a standstill.
• Equations show chemistry in action.
• I bought some powdered water, but I don't know
  what to add to it.

5
Writing Chemical Equations

• To write a chemical equation, you have to know
• What chemicals you are starting with
• What new chemicals you get during the reaction.
• Then you can use symbols to stand for the
  elements and compounds involved.
• Experience is something you don't get until just
  after you need it.

6
Symbols

• Most elements are represented by a one-letter or
  two-letter symbol.
• What's another word for Thesaurus?

7
Chemical Formulas

• A compound is represented by a word, called a
  chemical formula, which shows the ratio of
  elements in the compound.
• Change is inevitable except from vending
  machines.

8
Subscripts

• Look at H2O
• Notice that the number 2 is smaller than the
  letters.
• This Subscript shows the number of atoms of an
  element in a molecule.
• If a symbol does not have a subscript, the number
  1 is understood to be there.
• What happens if you get scared half to death
  twice?

9
Structure of an Equation Shows

• the reactants which enter into a reaction.
• the products which are formed by the reaction.
• the amounts of each substance used and each
  substance produced.
• Reactant Reactant --gt Product
• All those who believe in psychokinesis, raise my
  hand.

10
Coefficients

• A coefficient is a number in front of a chemical
  formula in the equation.
• It tells you how many molecules or atoms of each
  reactant and product take part in the reaction.
• If the coefficient is 1, you dont need to write
  it.

11
Conservation of Mass

• Matter is neither created nor destroyed,
  according to the law of conservation of mass .
• The number of atoms before and after a reaction
  does not change. Atoms are not lost.
• For my birthday I got a humidifier and a
  de-humidifier. I put them in the same room and
  let them fight it out.

12
(Still conserving that mass!)

• Consider the following reaction
• Hydrogen Gas Oxygen Gas ? Water
• The formula for each molecule above is correct.
  However, it seems that we have gained an extra
  oxygen atom. This is not possible. Something is
  wrong.
• I saw a bank that said "24 Hour Banking", but I
  don't have that much time.

13
Balancing Chemical Equations

• Balancing this equation will satisfy the law of
  conservation of mass. See the solution above
• Hydrogen Gas Oxygen Gas ? Water
• I almost had a psychic girlfriend but she left
  me before we met.

14
An example of equation balancing

• Let's say I ask you the following thing on a
  test
• "Balance the equation that takes place when
  sodium hydroxide reacts with sulfuric acid to
  form sodium sulfate and water."
• How do we solve this?
• I went to a general store. They wouldn't let me
  buy anything specifically.

15
One methodDraw boxes around all the chemical
formulas.

• You're drawing those boxes so that you'll be sure
  not to mess around with the formulas to balance
  the equation.
• I watched the Indy 500, and I was thinking that
  if they left earlier they wouldn't have to go so
  fast.

16
Make an element inventory

• In this inventory, your job is to figure out how
  many atoms of each element you have on the left
  and right sides of the equation.
• I went to a restaurant that serves "breakfast at
  any time". So I ordered French Toast during the
  Renaissance.

17
Balancing Equations

• Add coefficients to equations as needed.
• Do not change the formulas inside the boxes.
  That means count, but do not change subscripts.
• Final count of elements in reactants (before)
  must balance elements in product (after).
• The sign said "eight items or less". So I
  changed my name to Les.

18
Balance this!

• Magnesium Oxygen --gt Magnesium Oxide
• Mg O2 --gt MgO
• ?
• 2Mg O2 --gt 2MgO

19
Balance This!

• Nitrogen Hydrogen --gt ammonia
• N2 H2 --gt NH3
• ?
• N2 3H2 --gt 2NH3

20
Balance This!

• NaCl BeF2 --gt NaF BeCl2
• ?
• 2 NaCl BeF2 --gt 2 NaF BeCl2

21
Balance This!

• CH4 O2 --gt CO2 H2O
• ?
• CH4 2O2 --gt CO2 2H2O

22
Balance This!

• Mg Mn2O3 --gt MgO Mn
• ?
• 3Mg Mn2O3 --gt 3MgO 2Mn

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