CHEMICAL REACTIONS The Process of Chemical Change – or – “What the heck have I just made?”

CHEMICAL CHANGES In a chemical change a new substance is formed Signs of a chemical change ◦ Color change ◦ Change in odor ◦ Release of a gas ◦ Precipitate – solid formed suddenly in a liquid solution

CHEMICAL CHANGES Energy changes ◦ Temperature change ◦ Flame or explosion ◦ Luminescence or fluorescence Chemical equations – a way of describing a reaction Reactants and products ◦ reactant 1 + reactant 2  products

CHEMICAL EQUATIONS Word equations acetic acid + sodium bicarbonate  sodium acetate + carbon dioxide + water Chemical equations HC 2 H 3 O 2 + NaHCO 3  NaC 2 H 3 O 2 + CO 2 + H 2 O

CHEMICAL EQUATIONS Change to a chemical equation: Calcium + fluorine gas  calcium fluoride Ca + F 2  CaF 2

Chemical Equations Symbols for physical state (s) = solid (l) = liquid (g) = gas (aq) = aqueous (dissolved in water) HC 2 H 3 O 2(aq) + NaHCO 3(s)  NaC 2 H 3 O 2(aq) + CO 2(g) +H 2 O (l)

Energy in Chemical Reactions Energy in chemical reactions ◦ Exothermic reactions – heat is released ◦ Reaction vessel feels warm Energy appears on the right side of the equation as a product C 2 H 5 OH + 3O 2  2CO 2 + 3H 2 O + energy

ENERGY Endothermic reactions ◦ Take in energy from the surroundings ◦ Reaction container gets cold ◦ Energy appears on the left side of the equation as a reactant energy+Ba(OH) 2(s) +2NH 4 NO 3(s)  Ba(NO 3 ) 2(aq) +2H 2 O (l) +2NH 3(g)

BALANCING EQUATIONS Law of conservation of matter and energy ◦ Matter and energy cannot be created or destroyed – only interconverted ◦ All the atoms in the reactants show up in the products

Balancing Equations Coefficients – used to indicate numbers of molecules or formula units 5NaCl (five formula units of sodium chloride) 2H 2 O (two molecules of water)

Balancing Equations Counting atoms 5NaCl means five sodium atoms and five chlorine atoms 2H 2 O means four (2x2) hydrogen atoms and two oxygen atoms

Balancing Equations 3Ca(OH) 2 means three calcium atoms, six (3x2) oxygen atoms and six hydrogen atoms Multiply the subscript times the coefficient for every atom in the parentheses

Balancing Equations 4Ba(NO 3 ) 2 4 barium atoms, 8 (4x2) nitrogen atoms, and 24 (4x3x2) oxygen atoms 2Na 2 CO 3. 10H 2 O 4 (2x2) sodium atoms, 2 carbon atoms, 26 (2x3 + 10x2) oxygen atoms, and 40 (2x10x2) hydrogen atoms

Balancing Equations There must be the same number of atoms on each side of the equation H 2 + O 2  H 2 O 2 2H 2O 4H 2O2H 2O 2H 1O 2 4H 2O  4H 2O

Balancing Equations NaI + BaCl 2  NaCl + BaI 2(s) 2 1Na 1I 1Ba 2Cl 1Na 1Cl 1Ba 2I1Na 1I 1Ba 2Cl 2Na 2Cl 1Ba 2I2Na 2I 1Ba 2Cl  2Na 2Cl 1Ba 2I 2 Polyatomic ions can be counted as a group if they appear on both sides AgNO 3 + Na 2 SO 4  Ag 2 SO 4(s) + NaNO Ag 1NO 3 2Na 1SO 4 2Ag 1SO 4 1Na 1NO 3 2Ag 2NO 3 2Na 1SO 4 2Ag 1SO 4 1Na 1NO 3 2Ag 2NO 3 2Na 1SO 4  2Ag 1SO 4 2Na 2NO 3

Types of Chemical Reactions Synthesis reaction A + B  C C + O 2  CO 2 2Na + Cl 2  2NaClNa + Cl 2  NaCl

Types of Chemical Reactions Decomposition C  A + B H 2 O  H 2 + O 2 KClO 3  KCl + O 2 2KClO 3  2KCl + 3O 2 (NH 4 ) 2 Cr 2 O 7  N 2 +4H 2 O+Cr 2 O 3 22

Types of Chemical Reactions Single displacement A + BC  AC + B Metals displace metals, nonmetals displace nonmetals Fe + CuSO 4  Cu + FeSO 4 Cl 2 +2NaBr (aq)  Br 2 +2NaCl (aq) Cl 2 +NaBr (aq)  Br 2 +NaCl (aq)

Types of Chemical Reactions Double displacement AB + CD  AD + CB Metals and nonmetals switch partners NaCl+AgNO 3  NaNO 3 +AgCl (s) 2KI + Pb(NO 3 ) 2  PbI 2 + 2KNO 3 KI+Pb(NO 3 ) 2  PbI 2(s) +KNO 3

Types of Chemical Reactions Combustion Element or compound reacting with oxygen 2Mg + O 2  2MgO 2H 2 + O 2  2H 2 O

Combustion Reactions Carbon containing compounds give CO 2 and water CH 4 + O 2  CO 2 + H 2 OCH 4 + 2O 2  CO 2 + 2H 2 O C 2 H 5 OH+O 2  CO 2 +H 2 OC 2 H 5 OH+3O 2  2CO 2 +3H 2 O

Ionic equations Ionic equations have all aqueous salts written as ions Overall equation: ◦ K 2 S (aq) + CuCl 2(aq)  2KCl (aq) + CuS (s) Ionic equation: 2K + + S -2 + Cu Cl -  2K + + 2Cl - + CuS (s) Spectator ions: ions that appear on both sides of the equation in the same form

Net ionic equations Net ionic equations are ionic equations without the spectator ions. Ionic equation: 2K + + S -2 + Cu Cl -  2K + + 2Cl - + CuS (s) Net ionic equation: (take out spectators) Cu +2 + S -2  CuS (s) Write overall, ionic and net ionic equations for this reaction: magnesium reacts with aqueous nickel (II) nitrate to form nickel metal and aqueous magnesium nitrate.

Equilibrium Dynamic equilibrium occurs when the forward and reverse reactions happen at the same rate. N 2 + 3H 2  2NH 3 At equilibrium, ammonia is being made and decomposed at the same speed.

Equilibrium At equilibrium, the reaction seems to stop. In order to achieve equilibrium, reactions must be reversible, or able to occur in both directions.

LeChatelier’s Principle Position of equilibrium – how much product and reactant is present at equilibrium LeChatelier’s principle: If an equilibrium system is stressed, the system will shift to relieve the stress.

LeChatelier’s Principle Stresses – adding or removing reactants, products or energy. N 2 +3H 2  2NH 3 +energy 6H 2 O + CoCl 4 -2  Co[H 2 O] Cl - + energy blue pink Add Cl - Remove Cl - Add energy Remove energy

Kinetics Kinetics: reaction rates, or how fast does a reaction go Activation energy is the energy required to start a reaction Reaction rates are measured in units of (product)/(unit time)

Kinetics Factors affecting reaction rates ◦ Temperature ◦ Concentration/surface area  Limiting reagent – the reactant that is completely used up in a reaction ◦ Catalyst – a substance that speeds a reaction without being used up

Kinetics Inhibitor – a substance that slows a reaction.