Chapter 21 Chemical Reactions

Def: change in which one or more substances are converted into new substances Reactants  Products “yield”

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

Writing Equations Chemical Equation: describes a chemical rxn using formulas and symbols

Unit Managers Coefficients: represent number of units of each substance 2H 2 + O 2  2H 2 O coefficients

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. NiCl 2 (aq) + 2NaOH(aq)  Ni(OH) 2 (s) + 2NaCl(aq)

Chemical Rxns in the Environment Iron rusting – Iron(III) Oxide – Very damaging Aluminum reacts with O 2 – Aluminum Oxide – Coating, looks dull, protects Copper reacts with air – Blue-green coating – Patina

Balancing Equations Section 2

Bicycle Equation 4 main parts to bicycle – Frame (F) – Wheel (W) – Handlebar (H) – Pedal (P)Bicycle FW 2 HP 2 F + W + H + P  FW 2 HP 2 F + 2W + H + 2P  FW 2 HP 2

Balanced Equations Balanced Equation: has same # of atoms of each element on both sides of equation HgO(s)  Hg(l) + O 2 (g) Count atoms on each side Write in coefficients Reduce if needed

Let’s Balance!! Fe(s) + Cl 2 (g)  FeCl 3 (s) MgSO 4 + KNO 3  Mg(NO 3 ) 2 + K 2 SO 4 Li(s) + H 2 O(l)  LiOH(aq) + H 2 (g)

Types of Reactions Section 3

Types of Reactions Organize all rxns into 5 main types – Combustion – Synthesis – Decomposition – Single Displacement – Double Displacement

Synthesis Rxns Def: two or more substances combine to form another A + B  AB 1 Product!! 2H 2 (g) + O 2 (g)  2H 2 O(g)

Combustion Rxns Type of synthesis - Burning Def: substance reacts with oxygen to produce energy in the form of heat and light CH 4 (g) + 2O 2 (g)  CO 2 (g) + 2H 2 O(g)

Decomposition Rxns Opposite of Synthesis Rxns Def: one substance breaks down into two or more substances AB  A + B 1 Reactant!! 2H 2 O 2 (g)  2H 2 O (g) + O 2 (g) MnO 2

Single Displacement Def: one element replaces the other in a compound A + BC  AC + B 1 element and 1 compound!! Cu(s) + 2AgNO 3 (aq)  Cu(NO 3 ) 2 (aq) + 2Ag(s)

Double Displacement Def: + ion of one compound replaces the + ion in another compound May form a precipitate – an insoluble compound (doesn’t dissolve in H 2 O) AB + CD  AD + CB 2 compounds react!! Pb(NO 3 ) 2 (aq) + 2NaCl(aq)  PbCl 2 (s) + 2NaNO 3 (aq)

Chemical Rxns and Energy Section 4

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

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

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

Catalysts and Inhibitors Catalyst: speeds up a chemical rxn – Doesn’t change rxn, just makes it happen faster Inhibitors: slow down chemical rxn – Preservatives BHT, BHA prevent spoilage rxn Don’t change amount produced!!! Just speed or slow a rxn!!