Chapter 21

Chemical Reactions

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

2H2 + O2 2H2O

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.

NiCl2(aq) + 2NaOH(aq) Ni(OH)2(s) + 2NaCl(aq)

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

Balancing Equations

Section 2

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

Balanced EquationsBalanced 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

Let’s Balance!!

Fe(s) + Cl2(g) FeCl3(s)

MgSO4 + KNO3 Mg(NO3)2 + K2SO4

Li(s) + H2O(l) LiOH(aq) + H2(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!!

2H2(g) + O2(g) 2H2O(g)

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)

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

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)

Double Displacement Def: + ion of one compound replaces the + ion

in another compound May form a precipitate – an insoluble

compound (doesn’t dissolve in H2O) AB + CD AD + CB 2 compounds react!!

Pb(NO3)2(aq) + 2NaCl(aq) PbCl2(s) + 2NaNO3(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!!