Chemical Reactions

1
Chemical Reactions

• chemical reaction atoms rearrange to form new
  substances
• Reactions are caused by the movement of ________
  ______________.
• Evidence of a reaction (sometimes)

2
Chemical Equations

• reactants chemicals that you start with
• products chemicals formed during reaction
• A chemical equation looks like this
• reactants ? products
• which literally means
• reactants react to form products or reactants
  yield products

3
Symbols in Chemical Equations

(s)
(l)
(g)
(aq)
4
Symbols in Chemical Equations

• Zn(s) H2O(l) ? ZnO(s) H2(g)
• Na2CO3(aq) Ca(OH)2(aq) ? NaOH(aq) CaCO3(s)
• CaCO3(s) ? CaO(s) CO2(g)

5
Writing Chemical Equations

• Solid sodium oxide reacts with liquid water to
  form a solution of sodium hydroxide.
• Hydrogen chloride solution and zinc metal form
  zinc chloride (ZnCl2) solution and hydrogen gas
  (H2).

6
Chemical Equations
coefficients

• 2H2 O2 ? 2H2O
• subscript number of each atom in a compound
• - no subscript means there is 1 atom
• coefficient number of each compound - no
  coefficient means there is 1 compound

subscripts
7
Writing Chemical Reactions

• To get the total number of atoms, multiply the
  coefficient by the subscript.
• 4Fe 3O2 ? 2Fe2O3
• 4Fe means that there are 4 x 1 4 iron atoms on
  the reactant side
• 3O2 means that there are 3 x 2 6 oxygen atoms
  on the reactant side
• 2Fe2O3 means that there are 2 x 2 4 iron atoms
  and 2 x 3 6 oxygen atoms on the product side

8
Balancing Chemical Equations

• Law of Conservation of Mass states that what you
  put in is what you get out.
• In chemical reactions, that means that if you
  have 30 iron atoms on the reactant side, then
  there must be 30 iron atoms on the product side.
  They may be in different compounds, but the total
  number of atoms must be the same on each side.

9
Balancing Chemical Equations

• To balance an equation, change the coefficients
  to make the number of atoms of each element
  equal.
• DO NOT CHANGE THE SUBSCRIPTS!!
• Na Cl2 ? NaCl
• TiCl4 H2O ? TiO2 HCl
• Al F2 ? Al2F3

10
Balancing Chemical Reactions

• C3H8 O2 ? CO2 H2O
• Sb O2 ? Sb4O6
• N2O5 H2O ? HNO3

11
Balancing with Polyatomic Ions

• Still have to count the total number of each atom
  on each side. Multiply subscript outside
  parentheses by subscript inside parentheses.
• DO NOT CHANGE THE SUBCRIPTS!!
• HNO3 Cu ? Cu(NO3)2 H2
• B(CN)3 H2 ? B HCN
• Al(OH)3 HCl ? AlCl3 H2O

12
Balancing with Polyatomic Ions

• Ca3(PO4)2 SiO2 ? P4O10 CaSiO3
• Ca(ClO3)2 ? CaCl2 O2
• Ag2S KCN ? KAg(CN)2 K2S

13
Reaction Types

• synthesis two or more reactants form a single
  product
• A B ? AB
• Fe Cl2 ? FeCl3

14
Reaction Types

• decomposition single reactant breaks down into
  two or more products
• AB ? A B
• HgO ? Hg O2

15
Reaction Types

• single-displacement
• A BX ? AX B
• Cu AgNO3 ? Cu(NO3)2 Ag
• double-displacement
• AX BY ? AY BX
• NaOH CuCl2 ? NaCl Cu(OH)2

16
Reaction Types

• combustion oxygen reacts with another element
  or compound AND releases heat and light
• CH4 O2 ? CO2 H2O
• Sometimes combustion reactions are synthesis as
  well.
• Mg O2 ? MgO

17
Activity Series

• definition order of reactivity of elements
• (most reactive on top, least reactive on bottom)
• Element will displace element below it reaction
  occurs
• Element will NOT displace element above it
  reaction does NOT occur

18
Activity Series

• Predict whether or not the following reactions
  will occur.
• Na(s) MgBr2(aq) ?
• Mn(NO3)2(aq) Au(s) ?
• Hg(s) PtO(aq) ?

19
Predicting Reaction Products

1. If there is only one reactant, write the
   individual elements then skip to step 5.
2. If there is more than one reactant, label each
   atom/ion with charge.
3. Form resulting compounds using correct charge
   combinations ignore subscripts on the reactant
   side.
4. Using the charges, put the correct subscripts on
   the products.
5. Balance the reaction.

20
Reaction Prediction

• Determine the products and balance the rxn.
• K(s) Cl2(g) ?
• CaF2(aq) Li2S(s) ?
• BaS(s) ?
• Sr2N3(aq) Na2O(aq) ?