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Types of Reactions

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l Reactions fall into 5 categories. l We will recognize the type by the reactants.

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Synthesis Reactions l Synthesize - put together l Whenever two or more substances combine to form one single product, the reaction is called a synthesis reaction.

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A + B AB Examples of unbalanced synthesis reactions: Fe + O 2 Fe 2 O 3 CaO + H 2 O Ca(OH) 2 Synthesis Reactions

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Decomposition Reactions l decompose = fall apart l In a decomposition reaction, one compound breaks down into two or more simpler substances.

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AB A + B H2OH2O H2H2 O2O2 + NaHCO 3 H2H2 NaCO 3 + Decomposition Reactions Examples of unbalanced decomposition reactions:

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Single Replacement l In a single-displacement reaction, one element takes the place of another in a compound. l One reactant must be an element and one reactant must be a compound. l The products will be a different element and a different compound.

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AA+XB+BX Single Replacement Examples of unbalanced single replacement reactions: F 2 + LiCl LiF + Cl 2 MgCl 2 + Na NaCl + Mg

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Double Replacement l In double-displacement reactions, the positive portions of two ionic compounds are interchanged. l The reactants must be two ionic compounds or acids. l Double replacement reactions usually take place in aqueous solution.

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AB + CD AD + CB Pb(NO 3 ) 2 + KI PbI 2 + KNO 3 HCl + KOH KCl + H 2 O Double Replacement Examples of unbalanced double replacement reactions:

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Combustion l A combustion reaction is one in which a substance rapidly combines with oxygen to form one or more oxides. l Combustion reactions involve a compound composed of only C and H (and maybe O) that is reacted with oxygen gas.

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Combustion l If the combustion is complete, the products will be CO 2 and H 2 O. l Combustion reactions produce heat, and are therefore considered exothermic reactions.

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C x H y + O 2 CO 2 + H 2 O + energy C 6 H 12 O 6 + O 2 CO 2 + H 2 O Combustion Example of an unbalanced combustion reaction:

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How to Recognize Which Type l Look at the reactants. (E = element; C = compound) l E + E Synthesis l CDecomposition l E + CSingle replacement l C + CDouble replacement l CH cpd + O 2 Combustion

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Problem l Identify whether the reaction is synthesis, decomposition, single replacement, double replacement or combustion. H 2 + O 2 H 2 O (synthesis) (decomposition)

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Problem l Identify whether the reaction is synthesis, decomposition, single replacement, double replacement or combustion. Mg(OH) 2 + H 2 SO 3 HgO (double replacement) (decomposition)

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Problem l Identify whether the reaction is synthesis, decomposition, single replacement, double replacement or combustion. KBr + Cl 2 Zn + H 2 SO 4 (single replacement)

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Problem l Identify whether the reaction is synthesis, decomposition, single replacement, double replacement or combustion. AgNO 3 + NaCl C 6 H 6 + O 2 (double replacement) (combustion)