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. • 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 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 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 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 LOOK AT TWO OF THE REACTION TYPES: SYNTHESIS AND DECOMPOSITION
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 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, 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 2 O H 2 CO 3(aq) TYPICAL EXAMPLE , RAINWATER
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 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 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 • 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
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