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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!!