CHEMICAL REACTIONS Equations Types of Reactions Prediction of Products Diatomic Molecules Solubility Rules

Chemical Reactions Substances undergo changes to produce new substances with different properties Represented by chemical equations Obey the law of conservation of mass Can be endothermic or exothermic

Evidence of a Chemical Reaction Change in temperature Formation of a precipitate (insoluble compound) Change in color Smoke Bubbles Production of light

Chemical Equations Use symbols and formulas to represent chemical reactions Include state symbols: (s) solids (l) liquids (g) gases (aq) solid dissolved in water…see solubility chart

Special Elements Diatomic Molecules Others Hydrogen Nitrogen Oxygen Fluorine Chlorine Bromine Iodine Others Phosphorus (P4) Sulfur (S8)

Parts of a Chemical Equation Reactants Substances that enter into a reaction Products Substances that are produced by a reaction State symbols Indicate the state of matter for each substance in the reaction Coefficients Indicate the number of molecules or atoms of each substance in a reaction

Chemical Equation PRODUCTS REACTANTS State symbols Coefficients Yields/Produces PRODUCTS REACTANTS 2H2 (g) + O2 (g)  2H2O (l) State symbols Coefficients

Why Balance? Equations must be balanced in order to satisfy the law of conservation of mass According to “the law” the mass of the reactants must be equal to the mass of the products

Find Masses 2H2 (g) + O2 (g)  2H2O (l)

How to Balance an Equation Write the correct formulas/symbols for the reactant and the products (check for diatomic molecules) Determine the number of atoms/ions of each element in the reactants and the products Add/change coefficients to make the numbers of atoms/ions equal for reactants and products. NEVER change subscripts!!!

Helpful Hints Balance oxygen last and hydrogen next to last Keep polyatomic ions “together” as long as they are together in the reactants and in the products

Balancing Equations Examples MgCl2 + K  KCl + Mg Pb(SO4)2 + KCl  PbCl4 + K2SO4

Balancing Equations Practice H2O2  H2O + O2 Na2CO3 + HCl  NaCl + H2O + CO2 FeCl3 + NH4OH  Fe(OH)3 + NH4Cl S8 + O2  SO3

Word Equations Expresses a chemical reaction in words rather than using formulas and symbols You will need to be able to convert from word equations to chemical equations and vice versa

Write word equations for: H2O2  H2O + O2 Na2CO3 + HCl  NaCl + H2O + CO2 FeCl3 + NH4OH  Fe(OH)3 + NH4Cl S8 + O2  SO3

Types of Reactions Synthesis Decomposition Single-Replacement Double-Replacement Combustion

Synthesis + Two or more substances react to form one substance General equation: A + X  AX Mg O +

Decomposition One substance breaks down (decomposes) to form more than one substance General Equation: AX  A + X K Cl +

Single Replacement A single element takes the place of another element in a compound. Can be a cation replacing another cation or an anion replacing another anion The “replacer” must be more reactive than the “replacee” See the Activity Series of Metals General Equation: AX + B  BX + A AX + Y  AY + X

Activity Series of Metals K Na Li Ca Mg Al Zn Fe Ni Sn Pb H Cu Hg Ag Au Decreasing Reactivity Will replace H+ from acids and water Will replace H+ from acids ONLY Activity Series of Metals

Single Replacement Li K F + No RXN Li Li + Br Br + F F

Will It React? Virtual Lab

Double Replacement The cations and anions in two compounds switch places The cation of one compound combines with the anion of the other compound and vice versa General Equation: AX + BY  AY + BX

Double Replacement K Br Na Cl +

Combustion A substance reacts with oxygen Combustion means “burn” The complete combustion of a hydrocarbon produces carbon dioxide and water Incomplete combustion can lead to the production of carbon monoxide

Identify the Type of Reaction Sb + O2  Sb4O6 H3BO3  H4B6O11 + H2O Al + FeO  Al2O3 + Fe FeCl3 + NH4OH  Fe(OH)3 + NH4Cl C7H16 + O2  CO2 + H2O