Ch. 7 More Chemical Reactions

Remember This… Law of Conservation of Mass - Mass cannot be created or destroyed but is conserved (can be changed toanother form)

Moles  mole = the amt of a substance that contains approx x particles of that substance  1 mole = Avogadro’s # = 6.02 x  Molar Mass = the mass (g) of 1 mole of a substance  Ex: 1 mol H 2 = 2.0 g  Ex: 1 mol O 2 = 32.0 g  Ex: 1 mol H 2 O = 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 of eggs before we run out of brownie mix packages 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 O 2 (can produce heat &/or light)

Everyday Chemical Reactions  Chemical reaction where an element loses electrons = oxidation  2Fe + 3O 2 Fe 2 O 3  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 When compounds form chemical bonds they give off energy May be in the form of heat &/or light May be in the form of heat &/or light When compounds break chemical bonds, they require energy When compounds break chemical bonds, they require energy (ex. – igniter for gas grills) (ex. – igniter for gas grills)

Endo- & Exo- If a chemical change causes energy to be released, it is exothermic reaction. 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. 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 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 How fast the reaction is happening Affected by: Affected by: Temperature Temperature Surface Area Surface Area Concentration Concentration Stirring Stirring Catalysts Catalysts

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

Surface Area More surface area = more reactions because there are more molecules to collide More surface area = more reactions because there are more molecules to collide (ex. – dust particles in grain bin) (ex. – dust particles in grain bin)

Concentration More particles in a certain volume = more collision reactions More particles in a certain volume = more collision reactionsStirring Moving the particles around (ex. -washing machine) increases the collision reactions Moving the particles around (ex. -washing machine) increases the collision reactions

Catalyst Speeds up reaction collisions by “matchmaking” the compounds or elements 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 Causes chemical reactions to happen more quickly but is not actually used up during the reactions

Equilibrium Nature strives for balance = 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 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) (Ex. Water in a bottle – some is evaporating at the same time some is condensing) H 2 O(l)H 2 O(g)