2. Types of Reactions

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

4. 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.

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

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

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

8. 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.

9. A→A+XB+BX Single Replacement Examples of unbalanced single replacement reactions: F 2 + LiCl  LiF + Cl 2 MgCl 2 + Na  NaCl + Mg

10. 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.

11. 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:

12. 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.

13. 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.

14. 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:

15. 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

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

17. 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)

18. 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)

19. 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)