Chapter 6: Understanding Chemical Reactions

Chapter 6:Understanding Chemical Reactions

Scientific Law • Scientific law is a general statement that sums up the conclusions of many experiments, or a statement that summarizes an observed pattern in nature.

The Law of Conservation of Mass • In a chemical reaction, the total mass of the reactants is always equal to the total mass of the products. (in a closed system) • Atoms are not destroyed in a chemical reaction, just rearranged.

Word Equations • Simple, but efficient method of representing a chemical reaction. • Indicates what reacts and what is produced. • Help chemists recognize patterns and to predict the products of a chemical reaction. • Reactant 1 + Reactant 2  Product 1 + Product 2

Balancing Equations • Write the word equation for the reaction. • Write the skeleton equation by replacing each name with the correct formula. • Count the number of atoms of each type found in the reactants and the products. • Multiple each of the formulas by the appropriate coefficients to balance the number of atoms.

Balancing Equations 1. Magnesium + oxygen gas  Magnesium oxide 2. Mg + O2 MgO 3. Elements Reactants Products Mg 1 1 O 2 1 4. 2 Mg + O2  2 MgO Elements Reactants Products Mg 2 2 O 2 2

Types of Chemical Reactions • Synthesis or Combination • Decomposition • Single Displacement • Double Displacement or Metathetic • Neutralization (special double displacement) 6. Combustion – complete and incomplete

Synthesis or Combination Reactions • Involve the combination of smaller atoms and/or molecules into larger molecules. • Often elements combine to form compounds. • A + B  AB

Synthesis or Combination Reactions • Important in the production of; • Medicines • Plastics (polymers) • Flavourings Acid + Alcohol  Ester • High energy Fuels

Synthesis or Combination Reactions • 2 H2 + O2 2 H2O • HCl + NH3  NH4Cl • CO2 + H2O  H2CO3 • N2 + 3 I2  2 NI3 • 4 Fe + 3 O2  2 Fe2O3 • 2 Na + Cl2  2 NaCl • 2 Mg + O2  2 MgO

Decomposition Reactions • Involve the splitting of a large molecule into elements or smaller molecules. • At least 2 products are formed. • Opposite of synthesis. • AB  A + B

Decomposition Reactions Speed up the breakdown of; • Waste & Toxic wastes • Explosives • Fats Slowdown the breakdown of; • Anti-rusting • Anti-aging

Decomposition Reactions • 2 H2O  2 H2 + O2 • 2 NI3  N2 + 3 I2 • NH4NO3  N2O + 2 H2O • ZnCO3  ZnO + CO2 • CuCO3  CuO + CO2 • 2 H2O2 2 H2O + O2 • CuSO4·5H2O  CuSO4 + 5 H2O

Single Displacement Reactions • Chemical changes that involve an element and a compound as reactants. • One element replaces or displaces another element from the compound. • X + AB  AX + B • Y + AB  YB + A

Single Displacement Reactions Important in; • Sacrificial corrosion • Extraction • Purification

Single Displacement Reactions • Zn + FeCl2 Fe + ZnCl2 • Mg + 2 AgNO3  2 Ag + MgNO3 • Br2 + CaI2  I2 + CaBr2 • Cu + 2 AgNO3  2 Ag + Cu(NO3)2 • Zn + 2 HCl  H2 + ZnCl2

Double Displacement Reactions • Occur when elements in different compounds displace each other or exchange places. • Often result in the formation of a precipitate. • AB + XY  AY + XB

Double Displacement Reactions Involved in; Industrial Purification • sewage treatment • waste water recovery • toxic metal recovery

Double Displacement Reactions • Pb(NO3)2 + 2 KI  PbI2 + 2 KNO3 • CaCO3 + 2 HCl  H2CO3 + CaCl2 • BaCl2 + MgSO4  BaSO4 + MgCl2 • AgNO3 + NaCl  NaNO3 + AgCl • FeCl3 + 3 NaOH  Fe(OH)3 + 3 NaCl • Na2CO3 + CaCl2  CaCO3 + 2 NaCl

Neutralization: A Special Double Displacement Reaction • Often involve an acid and a base. • Can involve an acid and a corrosive compound. • The products formed are water and a salt.

Neutralization reactions • NaOH + HCl  NaCl + H2O (base) + (acid)  (salt) + (water) • 2 HCl + Na2CO3 2 NaCl + H2CO3 H2CO3 H2O + CO2 • KOH + CH3COOH + H2O + KC2H3O2

Combustion Reactions • The rapid reaction of a substance with oxygen to produce compounds called oxides. • Complete Combustion • Products are always H2Oand CO2 • CH4 + 2 O2 CO2 + 2 H2O • Incomplete Combustion • Not enough oxygen for complete combustion • Products are H2O, CO2, CO and C. • C3H8 + 7 O2  2C + 2CO + 2CO2 + 8 H2O

Chapter 6: Understanding Chemical Reactions