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Section 1 Describing Chemical Reactions. Chapter 8. Chemical Reaction. A chemical reaction is the process by which one or more substances change into one or more new substances. Reactants are the original substances in a chemical reaction.

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slide1

Section1 Describing Chemical Reactions

Chapter 8

Chemical Reaction

  • A chemical reaction is the process by which one or more substances change into one or more new substances.
  • Reactants are the original substances in a chemical reaction.
  • Products are the substances that are created in a chemical reaction.
slide3

Section1 Describing Chemical Reactions

Chapter 8

Evidence of a Chemical Reaction

signs of a chemical reaction

Visual Concepts

Chapter 8

Signs of a Chemical Reaction

Click below to watch the Visual Concept.

Visual Concept

precipitate

Visual Concepts

Chapter 8

Precipitate

Click below to watch the Visual Concept.

Visual Concept

slide6

Section1 Describing Chemical Reactions

Chapter 8

Evidence of a Chemical Reaction

  • solution color changes
  • solution bubbles
  • copper is used up
slide7

Section1 Describing Chemical Reactions

Chapter 8

Chemical Reaction Versus Physical Change

  • chemical change – new substance forms with properties that differ from original substance
    • density
    • boiling point
    • melting point
  • physical change - changes of state
    • evaporation
    • condensation
    • melting
    • freezing
slide8

Section1 Describing Chemical Reactions

Chapter 8

Reactions and Energy Changes

  • Energy can be released in a chemical reaction.
  • methane + oxygen  carbon dioxide + water + energy
  • Energy is a product.
  • Energy can be absorbed in a chemical reaction.
  • dinitrogen tetroxide +energy nitrogen dioxide
  • Energy is a reactant.
slide9

Section1 Describing Chemical Reactions

Chapter 8

Constructing a Chemical Equation

  • A chemical equation shows the chemical formulas and relative amounts of all reactants and products.
  • A word equation contains the names of the reactants and products.
  • Equations must be balanced.
slide10

Section1 Describing Chemical Reactions

Chapter 8

Writing a Word Equation or Formula Equation

methane + oxygen  carbon dioxide + water

?CH4 + ?O2  ?CO2 + ?H2O

slide11

Section1 Describing Chemical Reactions

Chapter 8

Equations and Reaction Information

  • Physical States
  • NaHCO3(s) + HC2H3O2(aq)  NaC2H3O2(aq) + CO2(aq) + H2O(l)
  • solid liquid

aqueous solutions

  • Reaction Conditions
  • 350°C, 25 000 kPa

N2(g) + 3H2(g)

2NH3(g)

catalyst

slide12

Section1 Describing Chemical Reactions

Chapter 8

Equations and Reaction Information

chemical equation

Visual Concepts

Chapter 8

Chemical Equation

Click below to watch the Visual Concept.

Visual Concept

slide14

Section2 Balancing Chemical Equations

Chapter 8

Reactions Conserve Mass

  • Mass cannot be created or destroyed by a chemical or physical change
  • Equations must be balanced.
  • ?Na + ?H2O  ?NaOH + ?H2
slide15

Section2 Balancing Chemical Equations

Chapter 8

Balancing Equations

  • The number of atoms for each element must be the same on the reactants’ side and on the products’ side.
  • Acoefficient multiplies the number of atoms of each element in the formula that follows.
  • H2O: 2 hydrogen atoms, 1 oxygen atom
  • 2H2O: 4 hydrogen atoms, 2 oxygen atoms
reading a chemical equation

Visual Concepts

Chapter 8

Reading a Chemical Equation

Click below to watch the Visual Concept.

Visual Concept

balancing a chemical equation by inspection

Visual Concepts

Chapter 8

Balancing a Chemical Equation by Inspection

Click below to watch the Visual Concept.

Visual Concept

slide18

Section2 Balancing Chemical Equations

Chapter 8

Balancing Equations

Sample Problem A

Balance the equation for the reaction of iron(III) oxide with hydrogen to form iron and water.

slide19

Section2 Balancing Chemical Equations

Chapter 8

Balancing Equations

  • Sample Problem A Solution
  • Identify reactants and products.
  • reactants products

Fe2O3 + H2  Fe + H2O

3

2

3

  • Count atoms
  • Insert coefficients.
slide20

Section2 Balancing Chemical Equations

Chapter 8

Reactions Conserve Mass

  • Balanced equations show mass conservation
  • ?Na + ?H2O  ?NaOH + ?H2
  • 2Na + 2H2O  2NaOH + H2
  • Never change subscripts to balance equations
  • Unbalanced: H2 + O2  H2O
  • Incorrect: H2 + O2  H2O2
  • H2O  H2O2
  • Correct: 2H2 + O2  2H2O
slide21

Section2 Balancing Chemical Equations

Chapter 8

Reactions Conserve Mass

slide22

Section2 Balancing Chemical Equations

Chapter 8

Polyatomic Ions can be balanced as a group

slide23

Section2 Balancing Chemical Equations

Chapter 8

Balancing Equations

Sample Problem C

Aluminum reacts with arsenic acid, HAsO3, to form H2 and aluminum arsenate. Write a balanced equation for this reaction.

slide24

Section2 Balancing Chemical Equations

Chapter 8

Balancing Equations

Sample Problem C Solution

1. Identify reactants and products.

reactants products

Al + HAsO3  H2 + Al(AsO3)3

2. Count Atoms

2

6

3

2

3. Insert coefficients

slide25

Section3 Classifying Chemical Reactions

Chapter 8

Combustion Reactions

  • A combustion reaction is a reaction of a carbon-based compound with oxygen.
  • Combustion of propane:
  • C3H8 + 5O2 3CO2 + 4H2O
  • Combustion of ethanol:
  • CH3CH2OH + 3O2  2CO2 + 3H2O
slide26

Visual Concepts

Chapter 8

Combustion Reaction

Click below to watch the Visual Concept.

Visual Concept

slide27

Section3 Classifying Chemical Reactions

Chapter 8

Synthesis Reactions

  • In a synthesis reaction a single compound forms from two or more reactants.
  • Two elements form a binary compound
  • C + O2 CO2
  • 2C + O22CO
  • Two compounds form a ternary compound
  • CaO(s) + H2O(l)  Ca(OH)2(s)
  • CO2(g) + H2O(l)  H2CO3(aq)
slide28

Visual Concepts

Chapter 8

Synthesis Reactions

Click below to watch the Visual Concept.

Visual Concept

slide29

Section3 Classifying Chemical Reactions

Chapter 8

Decomposition Reactions

  • In a decomposition reaction a single compound breaks down, often with the input of energy, into two or more elements or simpler compounds.
  • Decomposition of water

electricity

2H2O(l)

O2(g)+ 2H2(g)

  • A metal carbonate decomposes to form a metal oxide and carbon dioxide.

heat

CaCO3(s)

CaO(s) + CO2(g)

slide30

Visual Concepts

Chapter 8

Decomposition Reaction

Click below to watch the Visual Concept.

Visual Concept

electrolysis

Visual Concepts

Chapter 8

Electrolysis

Click below to watch the Visual Concept.

Visual Concept

slide32

Section3 Classifying Chemical Reactions

Chapter 8

Decomposition Reactions, continued

Sample Problem D

Predicting Products

Predict the product(s) and write a balanced equation for the reaction of potassium with chlorine.

slide33

Section3 Classifying Chemical Reactions

Chapter 8

Decomposition Reactions, continued

Sample Problem D Solution

  • Reaction is most likely a synthesis reaction, so the product will be binary
  • Potassium will lose one electron to become a 1+ ion.
  • Chlorine will gain one electron to become a 1– ion.
  • K + Cl2 KCl
  • Balance the equation.
  • 2K + Cl2 2KCl
slide34

Section3 Classifying Chemical Reactions

Chapter 8

Displacement Reactions

  • In adisplacement reactiona single element reacts with a compound and displaces another element from the compound.
  • 2Al(s) + 3CuCl2(aq)  2AlCl3(aq) + 3Cu(s)
  • Aluminum displaces copper.
slide36

Section3 Classifying Chemical Reactions

Chapter 8

Displacement Reactions, continued

  • The activity seriesranks the reactivity of elements
activity series

Visual Concepts

Chapter 8

Activity Series

Click below to watch the Visual Concept.

Visual Concept

slide38

Section3 Classifying Chemical Reactions

Chapter 8

Displacement Reactions, continued

Sample Problem E

Determining Products by Using the Activity SeriesMagnesium is added to a solution of lead(II) nitrate. Will a reaction happen? If so, write the equation and balance it.

slide39

Section3 Classifying Chemical Reactions

Chapter 8

Displacement Reactions,continued

Sample Problem E Solution

  • Identify the reactants.
  • Magnesium will attempt to displace lead from lead(II) nitrate.
  • Check the activity series.
  • Magnesium is more active than lead and displaces it.
  • Write the balanced equation.
  • Mg + Pb(NO3)2 Pb + Mg(NO3)2
slide40

Section3 Classifying Chemical Reactions

Chapter 8

Double-Displacement Reactions

  • In adouble-displacement reactiontwo compounds in aqueous solution appear to exchange ions and form two new compounds.
  • One of the products must be a solid precipitate, a gas, or a molecular compound, such as water.
  • HCl(aq) + NaOH(aq)  HOH(l) + NaCl(aq)
slide41

Visual Concepts

Chapter 8

Double-Displacement Reaction

precipitation reaction

Visual Concepts

Chapter 8

Precipitation Reaction

Click below to watch the Visual Concept.

Visual Concept

slide43

Chapter 8

  • Identifying Reactions and Predicting Products