Describing a Chemical Reaction Indications of a Chemical Reaction –Evolution of heat, light, and/or sound –Production of a gas –Formation of a precipitate –Color change

ENERGY CHANGES IN REACTIONS: determined by CHANGES that occur IN chemical BONDING. Chemical reactions involve the BREAKING of chemical BONDS in reactants and the FORMATION of chemical BONDS in products. Example: In the combustion of propane, the bonds in propane and oxygen molecules are broken, while the bonds in carbon dioxide and water molecules are formed. C 3 H O 2 ——> 3 CO 2 + 4H heat

LAW OF CONSERVATION OF ENERGY In an exothermic reaction, the chemical energy of the reactants is CONVERTED INTO HEAT plus the chemical energy of the products. In an exothermic reaction, the chemical energy of the reactants is CONVERTED INTO HEAT plus the chemical energy of the products. In an endothermic reaction, HEAT plus the chemical energy of the reactants IS CONVERTED into the chemical energy of the products. In an endothermic reaction, HEAT plus the chemical energy of the reactants IS CONVERTED into the chemical energy of the products. In both cases, the total amount of ENERGY BEFORE AND AFTER the reaction IS THE SAME.

Chemical Equations Reactants – the substances that exist before a chemical change (or reaction) takes place. Products – the new substance(s) that are formed during the chemical changes. CHEMICAL EQUATION indicates the reactants and products of a reaction. REACTANTS  PRODUCTS

Word Equations A WORD EQUATION describes chemical change using the names of the reactants and products. REMEMBER conservation of mass when converting to chemical equation Write the word equation for the reaction of methane gas with oxygen gas to form carbon dioxide and water. methane + oxygen carbon dioxide + water Reactants Products

TYPES OF CHEMICAL REACTIONS 1. Oxidation-Reduction (gain/loss of electrons) a. Synthesis – 2 or more substances form a new single substance b. Decomposition – One substance breaks down into simpler substances c. Single-displacement – A single element displaces another element from a compound d. Combustion – A compound reacts with O 2 to form H 2 O

TYPES OF CHEMICAL REACTIONS 2. Double Displacement (reactions where two elements or groups of elements in two different compounds exchange places to form two new compounds) a. Precipitation – T wo soluble substances form an insoluble precipitate b. Acid-Base – An acid reacts with a base to form a “salt” and water c. Gas Evolution – A gas is formed

SYNTHESIS REACTION: two or more substances react to FORM A SINGLE SUBSTANCE. A + B → AB SO 2 + O 2 → SO 3 CO + O 2 → CO 2 P 4 O 10 + H 2 O → H 3 PO 4 CuBr + Br 2 → CuBr 2

DECOMPOSITION REACTION: a compound BREAKS DOWN into two or more simpler substances. AB → A + B H 2 CO 3 → CO 2 + H 2 O NCL 3 → N 2 + CL 2 NaHCO 3 → CO 2 + Na 2 CO 3 + H 2 O

SINGLE-REPLACEMENT REACTION: one element TAKES THE PLACE of another element in a compound. A + BC → B + AC SiO 2 + Mg → Si + MgO Cu + HgNO 3 → Cu(NO 3 ) 2 + Hg Li + H 2 O → LiOH + H 2 H 2 SO 4 + Ca → CaSO 4 + H 2

COMBUSTION REACTION: a substance REACTS RAPIDLY WITH OXYGEN, often producing heat, light, CO 2 and water (overlaps with other types). CH 4 + O 2 → CO 2 + 2H 2 O C 4 H 10 + O 2 → CO 2 + H 2 O C 10 H 22 + O 2 → CO 2 + H 2 O CH 4 + O 2 → CO 2 + H 2 O

DOUBLE-REPLACEMENT REACTION: two different compounds EXCHANGE POSITIVE IONS and form TWO NEW COMPOUNDS. AB + CD → AD + CB CaCl 2 + K 3 PO 4 → Ca 3 (PO 4 ) 2 + KCl CaCO 3 + HCl → H 2 CO 3 + CaCl 2 AgSO 4 + NH 4 I → (NH 4 ) 2 SO 4 + AgI BaO + HNO 3 → Ba(NO 3 ) 2 + H 2 O Al 2 (SO 4 ) 3 + Ca(OH) 2 → Al(OH) 3 + CaSO 4

Phase Symbols Used in Chemical Equations “Yields”; indicates result of reaction Used to indicate a reversible reaction A reactant or product in the solid state; also used to indicate a precipitate Alternative to (s), but used only to indicate a precipitate A reactant or product in the liquid state A reactant or product in an aqueous solution (dissolved in water) A reactant or product in the gaseous state (s)(s) (l)(l) (aq) (g)(g)

Phase Symbols Used in Chemical Equations Alternative to (g), but used only to indicate a gaseous product Reactants are heated Pressure at which reaction is carried out, in this case 2 atm Pressure at which reaction is carried out exceeds normal atmospheric pressure Temperature at which reaction is carried out, in this case 0 o C Formula of catalyst, in this case manganese (IV) oxide, used to alter the rate of the reaction 2 atm pressure 0 o C MnO 2 

CH O 2  CO H 2 O Matter/Mass Conserved Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms Timberlake, Chemistry 7 th Edition, page 167

Balancing Chemical Equations Balanced Equation – one in which the number of atoms of each element as a reactant is equal to the number of atoms of that element as a product. Coefficients are used to balance, NOT subscripts What is the relationship between conservation of mass and the fact that a balanced equation will always have the same number of atoms of each element on both sides of an equation? Determine whether the following equation is balanced. H 2 + Cl 2  HCl

Balancing Chemical Equations 1. Write a word equation for the reaction. 2. Write the chemical equation for all reactants and products, then use MINOH. 3. Balance metal coefficients first (M). 4. Next, look for polyatomic ions, and balance coefficients as a group (I). 4. Then, balance non-metal coefficients (N). 5. Balance O and H last (OH).

1) Write a word equation for the reaction. Write a balanced equation for the reaction between iron (III) oxide and hydrogen to form iron and water 2) Write the correct formulas for all reactants and products. 3) Determine the coefficients that make the equation balance. Iron (III) oxide + hydrogen  iron + water Fe 2 O 3 + H 2 (g)  Fe + H 2 O Fe 2 O H 2 (g)  2 Fe + 3 H 2 O

1) Write a word equation for the reaction. Write a balanced equation for the reaction between chlorine and sodium bromide to produce bromine and sodium chloride. 2) Write the correct formulas for all reactants and products. 3) Determine the coefficients that make the equation balance. chlorine + sodium bromide  bromine + sodium chloride Cl 2 (g) + NaBr  Br 2 (g) + NaCl Cl 2 (g) + 2 NaBr  Br 2 (g) + 2 NaCl

1) Write a word equation for the reaction. 2) Write the correct formulas for all reactants and products. 3) Determine the coefficients that make the equation balance. aluminum sulfate + calcium chloride  calcium sulfate Al 2 (SO 4 ) 3 + CaCl 2  CaSO 4 (s) + AlCl 3 Write the balanced equation for the reaction between aluminum sulfate and calcium chloride to form a white precipitate of calcium sulfate. Al 2 (SO 4 ) CaCl 2  3 CaSO 4 (s) + 2 AlCl 3 + aluminum chloride

Ca Activity Series Foiled again – Aluminum loses to Calcium Element Reactivity Li Rb K Ba Ca Na Mg Al Mn Zn Cr Fe Ni Sn Pb H 2 Cu Hg Ag Pt Au Halogen Reactivity F 2 Cl 2 Br 2 I 2 Printable Version of Activity Series Printable Version of Activity Series

1) Write a word equation for the reaction. Write a balanced equation for the reaction between nitrogen trihydride and oxygen to form nitrogen monoxide and water. 2) Write the correct formulas for all reactants and products. 3) Determine the coefficients that make the equation balance. Nitrogen trihydride + oxygen  nitrogen monoxide + water NH 3 + O 2 (g)  NO + H 2 O 4 NH O 2 (g)  4 NO + 6 H 2 O

Cl H H H HH H H H 2 + Cl 2  HCl H 2 + Cl 2  2 HCl reactants products H Cl reactants products H Cl (unbalanced) (balanced) Coefficients are used to balance, NOT subscripts