Ch. 7 More Chemical Reactions

Remember This…

Law of Conservation of Mass - Mass cannot be created or destroyed

but is conserved (can be changed to another form)

Moles mole = the amt of a substance that

contains approx. 6.02 x 1023 particles

of that substance 1 mole = Avogadro’s # = 6.02 x 1023

Molar Mass = the mass (g) of 1 mole of a substance

Ex: 1 mol H2 = 2.0 g Ex: 1 mol O2 = 32.0 g Ex: 1 mol H2O = 18.0 g

Chemical Calculations Balanced Equation is like a recipe Tells how much of each “ingredient” is

needed for the product to turn out right If we need 2 eggs for each package of

brownie mix and we have 10 brownie mix packages and 1 dozen eggs

How many batches of brownies can we make?

Only 6 – because we will run out of eggs before we run out of brownie mix packages “Recipe” gives us a ratio for

the “ingredients”

Types of Reactions Synthesis – combine to form a

substance Decomposition – break down into

simpler substances (opposite of synthesis)

Single Replacement – 1 element takes the place of another in a compound

Double Replacement – two compounds exchange ions and form new compounds

Combustion – substance reacts with O2 (can produce heat &/or light)

Everyday Chemical Reactions Chemical reaction where an element loses

electrons = oxidation 2Fe + 3O2 Fe2O3 Iron + Oxygen Iron(III) Oxide (rust) A reactant is oxidized if it loses electrons

Chemical reaction where an element gains electrons = reduction

A reactant is reduced if it gains electrons Opposite of oxidation Oxidation & Reduction always occur

together = called Redox reactions

Indicators of Chemical Change Heat Light Exothermic Endothermic Development of Gas Forms Precipitant Color Change

Heat & Light When compounds form chemical

bonds they give off energy May be in the form of heat &/or light

When compounds break chemical bonds, they require energy

(ex. – igniter for gas grills)

Endo- & Exo-

If a chemical change causes energy to be released, it is exothermic reaction.

If energy is absorbed during a chemical change, it is an endothermic reaction.

Law of Conservation of Energy

Amount of energy before & after a chemical reaction will be the same

(although some energy may be converted into heat)

Reaction Rates How fast the reaction is happening

Affected by: Temperature Surface Area Concentration Stirring Catalysts

Temperature

Increasing temp. causes # of reactions to increase = faster reaction

Surface Area

More surface area = more reactions because there are more molecules to collide

(ex. – dust particles in grain bin)

Concentration More particles in a certain volume = more collision reactions

Stirring Moving the particles

around (ex. -washing machine) increases

the collision reactions

Catalyst

Speeds up reaction collisions by “matchmaking” the compounds or elements

Causes chemical reactions to happen more quickly but is not actually used up during the reactions

Equilibrium

Nature strives for balance = equilibrium

Chemical reactions are in a state of equilibrium if the forward & reverse reactions take place at the same rate

(Ex. Water in a bottle – some is evaporating at the same time some is condensing)

H2O(l) H2O(g)