Chemical Reactions

1
Chemical Reactions

• How do you know if a chemical reactions takes
  place?
• A color change takes place
• A solid (precipitate or ppt) forms
• Bubbles are formed without heating
• A flame occurs

2
Chemical Equations

• H2SO4 2 NaOH ? Na2SO4 2 H2O
• Reactants on the left, products on the right
• ? indicates a chemical reaction
• separates the substances
• 2 coefficient - how many of that substance (big
  number out front)
• 4 subscript how many of the preceding atom
  (little numbers)

3
Try this one

• Pb(NO3)2 2KI ? PbI2 2KNO3

subscript
coefficient
products
reactants
4
Law of Conservation of Mass

• Mass can not be created or destroyed in a
  chemical reaction. It can only change form.
• This means in a chemical reaction, there must be
  the same number of each type of atom on both
  sides of the arrow
  to make the equation
  balanced.

5
Balancing Equations

• Copy formulas correctly
• Subscripts can NOT be changed
• Change only the coefficients
• Determine the most complicated compound.
  Calculate the number of each atom/ion in that
  compound
• Coefficient x subscript of atoms/ions
• Go to other side of reaction, use coefficients to
  get the same number of ions/atoms
• Repeat until all ions are balanced.

6
Balancing Equations

• If your first guess of coefficients doesnt work,
  change your guess and start over.
• Be consistent balance the reactions the same
  way each time.
• Be right Know when to add numbers together, and
  when to multiply numbers together.

7
The 5 types of equations

• 1. Combination A B ? AB
• This forms a new compound from two or more
  reactants.
• 2 H2 O2 ? 2 H2O
• 2. Decomposition AB ? A B
• A single reactant breaks up into two or more
  products. This is the opposite of a combination
  reaction.
• 2 HgO ? 2 Hg O

8
The 5 types of equations

• 3. Single Replacement
• A BX ? AX B or A BX ? BA X
• An single element replaces an element in a
  compound. A metal replaces the metal, a nonmetal
  replaces the nonmetal in the compound.
• Cl2 2 NaBr ? 2 NaCl Br2
• Cs NaCl ? CsCl Na

9
The 5 types of equations

• 4. Double Replacement AB CD ? AD CB
• The positive ions in two different compounds are
  swapping places, or the negative ions in two
  different compounds are swapping places.
• H3PO4 3 NaOH ? Na3PO4 3 HOH

10
The 5 types of equations

• 5. Combustion
• CxHy (CxHyOz) O2 ? CO2 H2O
• Burning or the rapid oxidation of a carbon
  compound into carbon dioxide and water.
• CH4 2 O2 ? CO2 2 H2O
• 2 CH3OH 3 O2 ? 2 CO2 4 H2O

11
Tips for recognizing and balancing reactions

• Combination 2 reactants ? 1 product
• Decomposition 1 reactant ? 2 products
• Single element compound ? element compound
• Double elements in 2 compounds are exchanged
• Combustion CH(O) O2 ? CO2 H2O

12
Identify Each Type of Reaction

• _________________________ 3CaO P2O5 ?
  Ca3(PO4)2
• _________________________ Ca 2H2O ? Ca(OH)2
  H2
• _________________________ C2H4 3O2 ? 2CO2
  2H2O
• _________________________ 2KClO3 ? 2KCl 3O2
• _________________________ FeS 2HCl ? FeCl2
  H2S

13
Identify Each Type of Reaction

• _____combination_________ 3CaO P2O5 ?
  Ca3(PO4)2
• ____single replacement____ Ca 2H2O ? Ca(OH)2
  H2
• _____combustion_________ C2H4 3O2 ? 2CO2
  2H2O
• _____decomposition_______ 2KClO3 ? 2KCl 3O2
• _____double replacement___ FeS 2HCl ? FeCl2
  H2S

14
Predicting the products of reactions

• Identify the type of reaction combination,
  combustion or double replacement.
• Complete the reaction with the correct formulas
  based on the type of reaction.
• Balance the reaction once all of the complete
  formulas have been written.

15
Predicting Products

• Identify the type of reaction
• a.) Combination element element ?
• b.) Combustion CH(O) O2 ?
• c.) Double replacement compound compound ?

16
To complete the reaction with correct formulas

• a.) Combination the one compound formed will be
  the one formed from the elements as ions
• b.) Combustion the products will always be CO2
  and H2O
• c.) Double replacement switch the positive ions,
  get the correct formulas by cross method.
  Subscripts in the original compound dont matter
  unless they are part of the actual ion (a
  polyatomic ion).

17
Changing from word problems to equations

• HOFBrINCl or Lucky 7 H2 O2 F2 Br2
  I2 N2 Cl2
• Solid (s), liquid (l), gas (g), aqueous (aq)
• 2H2O2 (aq) ? 2H2O (l) O2 (g)
• 2Mg (s) O2 (g) ? 2MgO (s)
• Write all of the correct formulas, reactants on
  the left and products on the right.
• Balance the reaction