Chemical Reactions: Reactants change chemical and physical properties …. to become new substances made from the same elements; these are called products.

When you write a chemical reaction… The word equation explains what you begin with, and what you have at the end of the reaction. The reactants FORM, YIELD, or MAKE the products. Physical states may be included: (aq) = aqueous (l) = liquid (s) or (cr) = solid or crystalline (g) = gaseous Example: solid sodium reacts with water to form aqueous sodium hydroxide and hydrogen gas.

Types of Reactions Synthesis or Composition Decomposition Single Replacement Double Displacement Combustion Reactions A + B  AB AB  A + B AB + C  AC + B AB + CD  AD + CB C x H y + O 2  CO 2 + H 2 O HONCl BrIF A new twist To writing Formulas. These are Always written As diatomic Molecules.

Writing Equations: Subscripts describe the chemical composition of the substance. These are determined by the electrons in the atoms and MAY NOT BE CHANGED when balancing equations. Coefficients are used to balance equations. Na + Cl 2  NaCl 22

Composition/ Synthesis Reactions A + X  AX An element may react with oxygen to form the oxide (oxidation) A X

Composition/ Synthesis Reactions O 2 + 2Mg  2 MgO oxygen reacts with magnesium to form magnesium oxide O Mg O

Composition/ Synthesis Reactions C + O 2  CO 2 carbon reacts with oxygen to form carbon dioxide O C O

Practice predicting reactions with oxide and sulfides 1.2Fe + ____  2FeO 2.4 Fe + 3 ___  2 Fe 2 O 3 3.S O 2  8 ____ 4.8 Ba + S 8  8 ____ O2O2 O2O2 SO 2 BaS

More Composition/ Synthesis Reactions Fe + S  FeS Iron reacts with sulfur to form iron (II) sulfide Fe S Fe 2+ S 2-

More Composition/ Synthesis Reactions Na + S  Na 2 S Sodium reacts with sulfur to form sodium sulfide Na S Na + S 2- Na Na +

Metals react with halogens. 2Na + Cl 2  2 NaCl 2 Co + 3 F 2  2 CoF 3 2 K + I 2  2 KI Sr + Br 2  SrBr 2 2Mg + O 2  2 MgO

Synthesis reactions can also occur with oxides. Active metal oxides react with water to form hydroxides. ex: CaO + H 2 O  Ca(OH) 2 Many oxides of nonmetals react with water to form oxyacids. ex: SO 2 + H 2 O  H 2 SO 3 Some metal oxides react with nonmetal oxides to form salts. CaO + SO 2  CaSO 3

Practice Active metal oxides react with water to form hydroxides. ex: MgO + H 2 O  ________ Many oxides of nonmetals react with water to form oxyacids. ex: SO 3 + H 2 O  _________ Some metal oxides react with nonmetal oxides to form salts. Na 2 O + 2NO 2  ________ Mg(OH) 2 H 2 SO 4 2 NaNO 3

Decomposition AX  A + X 2H 2 O  2H 2 + O 2 O H H O H H Electrolysis: decomposition of a substance by an electric current.

Decomposition AX  A + X 2HgO  2Hg + O 2 O Hg O This reaction occurs when you heat orange colored mercury (II) oxide. Silver mercury and oxygen gas form.

Decomposition of metal carbonates ACO 3  AO + CO 2 (g) CaCO 3 (s)  CaO (s) + CO 2 (g) O Ca O This reaction occurs when you heat calcium carbonate. calcium oxide and carbon dioxide form. O C

Decomposition of metal hydroxides AOH  AO + CO 2 (g) Ca(OH) 2 (s)  CaO (s) + H 2 O (g) H Ca O This reaction occurs when you heat calcium hydroxide calcium oxide and water form. O H

Decomposition of metal chlorates AClO 3  ACl + O 2 (g) 2KClO 3 (s)  2KCl (s) + 3O 2 (g) K O This reaction occurs when you heat potassium chlorate. potassium chloride and oxygen form. Cl O K O O O O

Decomposition of acids H 2 CO 3 (aq)  H 2 O (g) + CO 2 (g) Carbonic acid decomposes when warmed. water and carbon dioxide form. O O O C H H

Single Displacement A+ BX  AX + B or: Y + BX  BY + X Replacement of a metal in a compound by another metal. 2 Al (s) + 3Pb(NO 3 ) 2  3Pb +2 Al(NO 3 ) 3 Al Pb 2+ N O O O N O O O N O O O N O O O N O O O N O O O

Single Displacement A+ BX  AX + B or: Y + BX  BY + X Replacement of a metal in a compound by another metal. 2 Al (s) + 3Pb(NO 3 ) 2  3Pb +2 Al(NO 3 ) 3 Al 3+ Pb N O O O N O O O N O O O N O O O N O O O N O O O

Single Displacement A+ BX  AX + B or: Y + BX  BY + X Replacement of a hydrogen in a compound by a metal. 2 Na (s) + 2 H 2 O (l)  2 NaOH (aq) + H 2 (g) Na O H H O H H

Single Displacement A+ BX  AX + B or: Y + BX  BY + X Replacement of a hydrogen in a compound by a metal. Mg (s) + 2 HCl (aq)  MgCl 2 (aq) + H 2 (g) Mg Cl H H

Single Displacement A+ BX  AX + B or: Y + BX  BY + X Replacement of halogens Cl 2 (g) + 2 KBr (aq)  2 KCl (aq) + Br 2 (g) Cl K Br K Cl

Double Replacement Reactions (double displacement) Formation of a precipitate. 2 KI (aq) + Pb(NO 3 ) 2 (aq)  PbI 2 (s) + 2 KNO 3 (aq) K K I Pb 2+ N O O O N O O O I

Double Replacement Reactions (double displacement) Formation of a gas. FeS (s) + 2 HCl(aq)  H 2 S (g) + FeCl 2 (aq) Fe 2+ S Cl H H

Double Replacement Reactions (double displacement) Formation of a water. NaOH (s) + HCl(aq)  H 2 O (l) + NaCl 2 (aq) Na + Cl H O H

Combustion Reactions A substance combines with oxygen, releasing a large amount of energy in the form of light and heat. 2 H 2 (g) + O 2 (g)  2 H 2 O O H H O H H

Combustion Reactions A substance combines with oxygen, releasing a large amount of energy in the form of light and heat. C 3 H 8 (g) +5 O 2 (g)  4 H 2 O + 3 CO 2 C CC H H H H H H H H O O O O O O O O O O

Combustion Reactions A substance combines with oxygen, releasing a large amount of energy in the form of light and heat. C 3 H 8 (g) +5 O 2 (g)  4 H 2 O + 3 CO 2 C C C H H H H H H H H O O O O O O O O O O