Types of Chemical Reactions I. Single replacement reaction II. Double replacement reaction III. Combination (synthesis) reaction IV. Decomposition reaction V. Combustion reaction

I. Single Replacement Reactions atoms of one element replace atoms of a second element in a compound a more reactive metal will replace any metal of less reactivity

Examples of single replacement reactions: Mg +Zn(NO 3 ) 2 Mg(NO 3 ) 2 + Zn Mg + 2AgNO 3 Mg(NO 3 ) 2 +2Ag Mg + LiNO 3 NR

II. Double Replacement Reactions positive ions switch generally involve two ionic compounds in aqueous solution are characterized by the production of a precipitate and….

one of the following is true: one product is only slightly soluble and precipitates from solution: Na 2 S (aq) +Cd(NO 3 ) 2(aq) CdS (s) + 2NaNO 3(aq) one product is a gas that bubbles out of the mixture: 2NaCN (aq) + H 2 SO 4(aq) 2HCN (g) +Na 2 SO 4(aq) Ca(OH) 2(aq) + 2HCl (aq) CaCl 2(aq) + 2H 2 O (l) one product is a molecular compound such as water:

Double replacement reactions in aqueous solutions most ionic compounds separate into cations and anions when dissolved in water (aqueous) complete ionic equation - shows dissolved ionic compounds as their free ions: Ag + (aq) + NO 3 - (aq) + Na + (aq) + Cl - (aq) AgCl (s) + Na + (aq) + NO 3 - (aq) precipitate! (What about these guys?)

They’re called…. Spectator ions appear in both sides of the equation, but are not directly involved in the reaction. spectator ions! Ag + (aq) + NO 3 - (aq) + Na + (aq) + Cl - (aq) AgCl (s) + Na + + NO 3 - (aq) How do you know which one will make the precipitate?

Copy the solubility rules from the chart on page 227. Practice predicting the formation of a precipitate: (write the products and circle the ppts.) H 2 SO 4 + BaCl 2 Al 2 (SO 4 ) 3 + 6NH 4 OH 2AgNO 3 + H 2 S CaCl 2 +Pb(NO 3 ) 2 Ca(NO 3 ) 2 + Na 2 CO 3 2HCl + BaSO 4 2Al(OH) 3 + 3(NH 4 ) 2 SO 4 2HNO 3 + Ag 2 S PbCl 2 + Ca(NO 3 ) 2 CaCO 3 + 2NaNO 3

III. Combination (synthesis) reactions: two or more substances combine to form a single substance reactants can be two elements or two compounds product is always a compound

5 possibilities: Group A metal + non-metal: compound is cation + anion 2K (s) + Cl 2(g) 2KCl (s) non- metal + non-metal: more than 1 combination is possible S (s) + O 2(g) SO 2(g) 2S (s) + 3O 2(g) 2SO 3(g)

transitional metal + non-metal: more than one product possible Fe (s) + S (s) FeS (s) 2Fe (s) + 3S (s) Fe 2 S 3(s) some non-metals + water: acid SO 2(g) + H 2 O (l) H 2 SO 3(aq) CaO (s) + H 2 O (l) Ca(OH) 2(aq) metallic oxide + water: base

IV. Decomposition reactions Compound breaks down into two simpler compounds (two or more products) CaO (s) +CO 2(g) Explosions are the result of extremely rapid decomposition reactions! ?? Why is energy required for decomposition reactions?? CaCO 3

V. Combustion Reactions an element or compound reacts with oxygen, producing energy as heat and light usually involve carbon and hydrogen with oxygen; large amounts of heat are released (fossil fuels) 2Mg (s) + O 2(g) → 2 MgO (s) C x H x + O 2 → CO 2 + H 2 O *other elements (such as S and Mg) react with O 2 to form combustion reactions:

Summary of reactions: Combination reaction: Decomposition reaction: Single-replacement reaction: Double-replacement reaction: Combustion reaction: X + YXY X + Y X + TYXY + T X + Y - + R + S - X + S - + R + Y - CH + O 2 CO 2 + H 2 O

How do you know if a chemical reaction has occurred? change in temperature change in color a gas is produced an odor is formed a solid is formed It’s like a baby’s diaper!