Types of chemical reactions Imagine that you are

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Types of chemical reactions • Imagine that you are baking some cookies at home.

Types of chemical reactions • Imagine that you are baking some cookies at home. • You follow a recipe • In the same way chemists know that elements and compounds undergo particular type of chemical reactions

 • How do you classify elements? • Chemical famillies • Members react in

• How do you classify elements? • Chemical famillies • Members react in a similar way How do we classify compounds? Ionic or molecular - Have definite patterns of chemical properties. • Chemists use these patterns to classify groups of chemical changes • 4 categories • • Synthesis Decomposition Single displacement Double displacement

 • Why is it useful to have any knowledge of of the types

• Why is it useful to have any knowledge of of the types of reactions? • We can better understand experimental observations. • We can predict products of unknown reactions

Look at the reactants represented below, which reaction involves elements as reactants? Which reaction

Look at the reactants represented below, which reaction involves elements as reactants? Which reaction involves compounds as reactants? Synthesis reaction A synthesis reaction involves the combination smaller molecules Decomposition reaction A decomposition reaction involves the breaking apart of larger molecules

Recognizing the types of reactants is key to identifying the reaction type LETS US

Recognizing the types of reactants is key to identifying the reaction type LETS US LOOK AT TWO OF THE REACTION TYPES: SYNTHESIS AND DECOMPOSITION

Synthesis Reactions • Involve the combination • General formula of smaller atoms and /or

Synthesis Reactions • Involve the combination • General formula of smaller atoms and /or molecules into • A + B AB larger molecules. • They are also called • If you see two elements combination reactions as reactants, you know the reaction has to be a sysnthesis reaction

 • Most of these elements are represented as single atoms, but some occur

• Most of these elements are represented as single atoms, but some occur naturally as diatomic molecules. For example, hydrogen and oxygen gases react to produce water hydrogen + oxygen H 2 + O 2 Element Diatomic molecule Hydrogen H 2 Oxygen O 2 Nitrogen N 2 Fluorine F 2 Chlorine Cl 2 Bromine Br 2 iodine I 2 2 H 2 + O 2 water H 2 O 2 H 2 O

 • Synthesis reactions can also involve combinations of small molecules. • For example,

• Synthesis reactions can also involve combinations of small molecules. • For example, when ammonia and hydrogen chloride vapours combine, they form a white smoke as solid particles of ammonium chloride are formed. Hydrogen chloride + ammonia ammonium chloride HCl + NH 3 NH 4 Cl

Similarly, combination of water and carbon dioxide molecules Synthesis reaction CO 2 + H

Similarly, combination of water and carbon dioxide molecules Synthesis reaction CO 2 + H 2 O H 2 CO 3(aq) TYPICAL EXAMPLE , RAINWATER

Decomposition Reactions • It involve the splitting of • Example, electrolysis of a large

Decomposition Reactions • It involve the splitting of • Example, electrolysis of a large molecule into water uses electricity to elements or smaller split water molecules. into their elements water hydrogen + oxygen • General formula H 2 O H 2 + O 2 AB A+ B 2 H 2 O 2 H 2 + O 2

 • Sometimes it involves large amounts of energy. • Nitrogen triiodide decomposes rapidly

• Sometimes it involves large amounts of energy. • Nitrogen triiodide decomposes rapidly to form the elements nitrogen and iodine nitrogen triiodide • NI 3 • 2 NI 3 nitrogen + iodine N 2 + I 2 N 2 + 3 I 2 • Can also involve the production of two small molecules from a large molecule • When ammonium nitrate is heated to above 250 o. C, it decomposes explosively to form nitrous oxide and water molecules • NH 4 NO 3 N 2 O + H 2 O • NH 4 NO 3 N 2 O + 2 H 2 O

Single Displacement Reactions Mg + Ag. No 3 Ag + Mg(NO 3)2 • Are

Single Displacement Reactions Mg + Ag. No 3 Ag + Mg(NO 3)2 • Are chemical changes that involve an element Mg + 2 Ag. NO 3 2 Ag + Mg(NO 3)2 and a compound as reactants. • One element displaces or replaces another element from the compound. • Example, when magnesium ribbon is placed in a solution of silver nitrate

Example, when the element bromine is added to a solution of calcium iodide •

Example, when the element bromine is added to a solution of calcium iodide • the bromine displaces (or takes the place of) the iodide ion • bromine + calcium iodide • Br 2 + Ca. I 2 iodine + calcium bromide I 2 + Ca. Br 2