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Chapter 5 Chemical Reactions. I. 5.1 Nature of Chemical Reactions II. 5.2 Reaction Types III. 5.3 Balancing Chemical Equations. I. 5.1 Nature of Chemical Reactions. A. Signs of a chemical reaction 1. bubbles are given off 2. changes in color 3. precipitates are formed

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Chapter 5 chemical reactions
Chapter 5 Chemical Reactions

  • I. 5.1 Nature of Chemical Reactions

  • II. 5.2 Reaction Types

  • III. 5.3 Balancing Chemical Equations


I 5 1 nature of chemical reactions
I. 5.1 Nature of Chemical Reactions

  • A. Signs of a chemical reaction

    • 1. bubbles are given off

    • 2. changes in color

    • 3. precipitates are formed

    • 4. energy is released or absorbed

  • B. Chemical reactions rearrange atoms


1. Reactants - a substance that undergoes a chemical change

a. bonds are broken

b. energy is added in the form of

(1) heat

(2) electricity

(3) sound

(4) light


2. Products - a substance that is the result of a chemical reaction

a. bonds are formed

b. energy is released in the form of

(1) heat

(2) light

(3) sound


3. Reactions can be referred to as reaction

a. Exothermic - a reaction that transfers energy from the reactants to the surroundings usually as heat

b. Endothermic - a reaction in which energy is transferred to the reactants usually as heat from the surroundings


Ii 5 2 reaction types
II. 5.2 Reaction Types reaction

  • A. Classifying Reactions

    • 1. We use patterns to identify the general types of chemical reactions


a. Synthesis reactions reaction

(1) a reaction of at least two substances that form a new, more complex compound

(2) general form

(a) A + B g AB

(b) 2 Na + Cl2g 2 Na Cl

i) subscript indicates the number of atoms per molecule

ii) coefficients indicates the number of molecules

iii) g is read as yields


b. Decomposition Reactions reaction

(1) a reaction in which one compound breaks into at least two products

(2) general form

(a) AB g A + B

(b) 2 H2O g 2 H2 + O2

(3) electrolysis is the decomposition of a compound by an electric current


c. Single Replacement (displacement) Reactions reaction

(1) a reaction in which atoms of one element take the place of atoms of another element in a compound

(2) general form

(a) XA + B g BA + X

(b) 3 CuCl2 + 2 Al g 2 AlCl3 + 3 Cu

(3) combustion a reaction in which a compound and oxygen burn

(a) 2 CH4 + 4 O2g 2 CO2 + 4 H2O


d. Double Replacement (displacement) Reactions reaction

(1) a reaction in which a gas, a solid precipitate, or a molecular compound is formed from the apparent exchange of ions between two compounds

(2) general form

(a) AX + BY g AY + BX

(b) Pb(NO3)2 + K2CrO4g PbCrO4 + 2 KNO3


e. Reduction/Oxidation (redox) reaction is a reaction that occurs when electrons are transferred from one reactant to another.

(1) reduced - substance that accept electrons

(2) oxidized - substance that gives up electrons


Iii 5 3 balancing chemical equations
III. 5.3 Balancing Chemical Equations occurs when electrons are transferred from one reactant to another.

  • A. Four Steps for Balancing Chemical Equations

    • 1. Determine the type of reaction.

      • a. D - Decomposition

      • b. S - Synthesis

      • c. SR - Single Replacement

      • d. DR - Double Replacement


2. Recombine ions/atoms on the product side. occurs when electrons are transferred from one reactant to another.

a. different free elements and different compounds

3. Balance compounds on the product side

a. using subscripts

b. check for diatomic elements

(1) only for Decomposition and Single Replacement reactions


4. Balance equation by placing coefficients in front of each compound or free element where necessary

a. Conservation of matter

b. must have the same number of atoms for each element on both sides of the equation

5. Examples

a. Mg + O2g

S

2 Mg + O2g 2 MgO

b. Pb(NO3)2 + KI g

DR

Pb(NO3)2 + 2 KI g PbI2 + 2 KNO3

c. N2 + H2g

d. NaCl g


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