SYNTHESIS AND DECOMPOSITION REACTIONS ELEMENTS AND THEIR OXIDES Chapter 4.1 & 5.3 SYNTHESIS AND DECOMPOSITION REACTIONS ELEMENTS AND THEIR OXIDES

Another good one: REVIEW: homework and major concepts from previous lesson (chem reaction, law of conservation of mass) http://www.funnyjunk.com/channel/Chemistry+Jokes+are+fun/cpmqGpc

Predicting Chemical Reactions Using the periodic table, we can figure out the properties of the elements Ex. H, N, O, F, Cl, Br, I elements are all diatomic Since the properties of the elements are predictable, the chemical reactions they undergo are also predictable Ex. Na and K are both alkali metals that react with Cl to form very stable compounds Because we can predict chemical reactions most of the time, chemists classify reactions. Today we will cover two types of chemical reactions.

Synthesis Reactions Two reactants combine to make a larger, more complex product What does it mean to synthesize something? Synthesis reaction between sodium and chlorine: http://www.youtube.com/watch?v=Mx5JJWI2aaw

Synthesis of Ionic Compounds Metal + Non-Metal  Ionic Compound Ex. 2 K (s) + Cl2 (g)  2 KCl (s) REMEMBER: Always apply the criss cross rule when making ionic compounds! Do the KCl equation on the board to show crossing of charges

Synthesis of Molecular Compounds Non-metal + Non-metal  Molecular compound Can involve: HYDROGEN: Easy to predict because H usually forms molecular compounds and follows general pattern of synthesis Ex. H2 (g) + F2 (g)  HF (g) NO HYDROGEN: difficult to predict because the reaction depends on reaction conditions. Ex. C and O can make CO or CO2 depending on the amount of oxygen available to react

Oxides– A Special Type of Synthesis Oxide: a compound made up of any element and oxygen Basic oxides Mg + O2  MgO MgO + H2O  Mg(OH)2 Acidic oxides CO2 (g) + H2O (l)  H2CO3 (aq) SO3 (g) + H2O (l)  H2SO4 (aq) NO2 (g) + H2O (l)  HNO3 (aq) + HNO2 (aq)

Recall: pH < 7 = acidic solution, pH= 7 neutral solution, pH > 7= basic solution Acids produce H+ ions in solution Bases produce OH- ions in solution

Decomposition Reactions A compound breaks down to form two or more simpler products Generally need energy (heat, catalyst, electricity) to get started What do you notice about this reaction? Opposite of synthesis

Decomposition of Ionic Compounds Ionic compound  Element + Element Ex. 2 KCl (l) 2 K (s) + Cl2 (g) This reaction involves passing electricity through KCl to break it down into its elements K and Cl

Decomposition Involving Compounds Compounds with polyatomic ions or molecular compounds are difficult to predict Use chemical tests to detect what the products are (often testing for presence of gas) Ex. 2 KClO3  2 KCl + 3 O2 Ex. CaCO3  CaO + CO2 Note: Both reactions require heat A chlorate will break down into a metal chloride and oxygen gas A carbonate will break down into a metal oxide and carbon dioxide

Examples Identify the reaction type: 2 HCl  H2 + Cl2 Cl2O (g) + H2O (l)  2 HClO (aq) 2 AlCl3 (s)  2 Al (s) + 3 Cl2 (g) KO (g) + H2O (l)  2 KOH (aq) Synthesis Synthesis – acidic oxide (nonmetal and oxygen) because of acid product Decomposition Synthesis – basic oxide (metal and oxygen) because of basic product

Some Helpful Links Synthesis and decomposition reactions explained: http://www.youtube.com/watch?v=yS8noHTIJ_E Basic and acidic oxides: http://www.youtube.com/watch?v=MtL64hRoTzQ

Homework pg. 161 # 1, 2, 4 pg. 204 #3, 4, 9