Chemical Reactions

1
Chapter 21

• Chemical Reactions

2
Chemical Reactions

• Def change in which one or more substances are
  converted into new substances
• Reactants ? Products

yield
3
Conservation of Mass

• Antoine Lavoisier 1770s
• Total mass of products always equals total mass
  of reactants
• Matter cannot be created or destroyed
• Father of Modern Chemistry

4
Writing Equations

• Chemical Equation describes a chemical rxn using
  formulas and symbols

5
Unit Managers

• Coefficients represent number of units of each
  substance
• 2H2 O2 ? 2H2O

coefficients
6
Writing Equations

• One unit of Nickel(II) chloride, dissolved in
  water, plus two units of sodium hydroxide,
  dissolved in water, produces one unit of solid
  nickel(II) hydroxide plus two units of sodium
  chloride, dissolved in water.
• NiCl2(aq) 2NaOH(aq) ? Ni(OH)2(s) 2NaCl(aq)

7
Chemical Rxns in the Environment

• Iron rusting Iron(III) Oxide
• Very damaging
• Aluminum reacts with O2 Aluminum Oxide
• Coating, looks dull, protects
• Copper reacts with air
• Blue-green coating
• Patina

8
Balancing Equations

• Section 2

9
Bicycle Equation

• 4 main parts to bicycle
• Frame (F)
• Wheel (W)
• Handlebar (H)
• Pedal (P) Bicycle FW2HP2
• F W H P ? FW2HP2
• F 2W H 2P ? FW2HP2

10
Balanced Equations

• Balanced Equation has same of atoms of each
  element on both sides of equation
• HgO(s) ? Hg(l) O2(g)
• Count atoms on each side
• Write in coefficients
• Reduce if needed

11
Lets Balance!!

• Fe(s) Cl2(g) ? FeCl3(s)
• MgSO4 KNO3 ? Mg(NO3)2 K2SO4
• Li(s) H2O(l) ? LiOH(aq) H2(g)

12
Types of Reactions

• Section 3

13
Types of Reactions

• Organize all rxns into 5 main types
• Combustion
• Synthesis
• Decomposition
• Single Displacement
• Double Displacement

14
Synthesis Rxns

• Def two or more substances combine to form
  another
• A B ? AB
• 1 Product!!
• 2H2(g) O2(g) ? 2H2O(g)

15
Combustion Rxns

• Type of synthesis - Burning
• Def substance reacts with oxygen to produce
  energy in the form of heat and light
• CH4(g) 2O2(g) ? CO2(g) 2H2O(g)

16
Decomposition Rxns

• Opposite of Synthesis Rxns
• Def one substance breaks down into two or more
  substances
• AB ? A B
• 1 Reactant!!
• 2H2O2(g) ? 2H2O (g) O2(g)

MnO2
17
Single Displacement

• Def one element replaces the other in a compound
• A BC ? AC B
• 1 element and 1 compound!!
• Cu(s) 2AgNO3(aq) ? Cu(NO3)2(aq) 2Ag(s)

18
Double Displacement

• Def ion of one compound replaces the ion in
  another compound
• May form a precipitate an insoluble compound
  (doesnt dissolve in H2O)
• AB CD ? AD CB
• 2 compounds react!!
• Pb(NO3)2(aq) 2NaCl(aq) ? PbCl2(s) 2NaNO3(aq)

19
Chemical Rxns and Energy

• Section 4

20
Energy Exchanges

• All rxns release or absorb energy
• Energy could be heat, light, sound, or
  electricity
• In rxns
• bonds breaking requires energy
• bonds forming releases energy

21
More Energy OUT

• Exergonic rxns release energy
• Less energy needed to break bonds than released
  to form bonds
• Light or heat is given off
• Exothermic rxn when energy given off is
  primarily heat
• Feels hot
• Ex burning wood, dynamite
• Provide most power to homes and industries

22
More Energy In

• Endergonic rxns absorb, take-in, energy
• Require more energy to break bonds then to form
  bonds
• Electricity often gives energy to rxns
• Endothermic rxn rxn absorbs heat
• Feels cold

23
Catalysts and Inhibitors

• Catalyst speeds up a chemical rxn
• Doesnt change rxn, just makes it happen faster
• Inhibitors slow down chemical rxn
• Preservatives BHT, BHA prevent spoilage rxn
• Dont change amount produced!!! Just speed or
  slow a rxn!!