chapter 9 chemical reactions. chapter 9 slide 2 of 37 physical change in a physical change, the...
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Chapter 9
Chemical Reactions
Chapter 9 Slide 2 of 37
Physical Change
In a physical change,
• The identity and composition of the substance do not change
• The state can change or the material can be torn into smaller pieces
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
Chapter 9 Slide 3 of 37
Chemical Change
In a chemical change,
• Reacting substances form new substances with different compositions and properties
• A chemical reaction takes place
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
Chapter 9 Slide 4 of 37
Chemical Reaction
In a chemical reaction,
• Old bonds are broken and new bonds are formed
• Atoms in the reactants are rearranged to form one or more different substances
• Fe and O2 form rust (Fe2O3)
Chapter 9 Slide 5 of 37
Chemical Reaction
In a chemical reaction,
• A chemical change produces one or more new substances
• There is a change in the composition of one or more substances
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
Chapter 9 Slide 6 of 37
Evidence of a Chemical Reaction
• Changes that can be seen are evidence of a chemical reaction.
Table 9.2
Chapter 9 Slide 7 of 37
Writing a Chemical Reaction
• Chemists use a shorthand approach when writing the specifics of a chemical reaction. This approach is called the chemical equation.
Reactants -----> Products
Chapter 9 Slide 8 of 37
Chemical Equations
A chemical equation,
• Gives the chemical formulas of the reactants on the left of an arrow and the products on the right
Reactants Product
C(s)
O2 (g)CO2 (g)
Chapter 9 Slide 9 of 37
Symbols Used in Equations
Symbols used in chemical
equations show:
• The states of the reactants
• The states of the products
• The reaction conditions
Table 9.3
Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
Chapter 9 Slide 10 of 37
Chemical Equations Are Balanced
In a balanced chemical reaction,
• Atoms are not gained or lost
Chapter 9 Slide 11 of 37
Chemical Equations Are Balanced
In a balanced chemical reaction,
• The number of reactant atoms are equal to the number of product atoms
Chapter 9 Slide 12 of 37
Chemical Equations•Chemical equations: symbolic descriptions of chemical reactions.•Two parts to an equation:
•reactants and products
H2 + O2 H2OA Chemical Equation must also be balanced.
2H2 + O2 --> 2H2O
Chapter 9 Slide 13 of 37
Balanced Chemical Equations
• Chemical Equations must be balanced– There must be equal numbers of atoms of
each element on both sides of the equation (both sides of the arrow)
1. Write the correct symbols and formulas for all of the reactants and products.
2. Count the number of each type of atom on BOTH sides of the equation.
3. Insert coefficients until there are the equal numbers of each kind of atom on both sides of the equation.
Chapter 9 Slide 14 of 37
A Balanced Chemical Equation
Al + S Al2S3 Not Balanced
How many atoms of Al and S are on each side of the equation?
coefficients
Al + S Al2S3
_ Al = _ Al
_ S = _ S
Chapter 9 Slide 15 of 37
Learning Check
State the number of atoms of each element on thereactant and on the product sides of the equations:
P4(s) + 6 Br2(l) → 4 PBr3(g)
Chapter 9 Slide 16 of 37
Learning Check
State the number of atoms of each element on thereactant and on the product sides of the equations:
2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s)
Chapter 9 Slide 17 of 37
Check the balance of atoms in the following:
Fe3O4(s) + 4H2(g) 3Fe(s) + 4H2O(l)
Learning Check
Chapter 9 Slide 18 of 37
Learning CheckDetermine if each equation is balanced or not.
Na(s) + N2(g) → NaN3(s)
C2H4(g) + H2O(l) → C2H5OH(l)
Chapter 9 Slide 19 of 37
Balancing Equations
• Methane reacts with oxygen (combustion reaction) to form carbon dioxide and water.
Write a properly balanced chemical equation
1. Write out chemical formulas
CH4 + O2 CO2 + H2O
2. Use coefficients to balance the equation
Chapter 9 Slide 20 of 37
The Numbers in Chemical Equations
Chapter 9 Slide 21 of 37
More Practice: Balancing Reactions
C2H6 + O2 CO2 + H2O
C3H6 + O2 CO2 + H2O
NH3 + O2 NO + H2O
Chapter 9 Slide 22 of 37
And more practice….
B2H6 + H2O H3BO3 + H2
C3H8O + O2 CO2 + H2O
Chapter 9 Slide 23 of 37
Balancing with Polyatomic Ions
MgCl2(aq) + Na3PO4(aq) NaCl(aq) + Mg3(PO4)2(s)
• HINT: Balance PO43- as a unit.
Set of # coef?
Chapter 9 Slide 24 of 37
Type of Reactions
Chemical reactions can be classified as
• Combination reactions.
• Decomposition reactions.
• Single Replacement reactions.
• Double Replacement reactions.
• Combustion reactions.
Chapter 9 Slide 25 of 37
Combination In a combination reaction,
• Two or more elements form one product.
• Or simple compounds combine to form one product.
+
2Mg(s) + O2(g) 2MgO(s)
2Na(s) + Cl2(g) 2NaCl(s)
SO3(g) + H2O(l) H2SO4(aq)
A B A B
Chapter 9 Slide 26 of 37
DecompositionIn a decomposition reaction,
• One substance splits into two or more simpler substances.
2HgO(s) 2Hg(l) + O2(g)
2KClO3(s) 2KCl(s) + 3O2(g)
Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
Chapter 9 Slide 27 of 37
Learning Check
Classify the following reactions as
A) combination or B) decomposition:
Chapter 9 Slide 28 of 37
Single ReplacementIn a single replacement reaction,
• One element takes the place of a different element in a reacting compound.
Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)
Fe(s) + CuSO4(aq) FeSO4(aq) + Cu(s)
Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
Chapter 9 Slide 29 of 37
Double ReplacementIn a double replacement reaction,• Two elements in the reactants exchange places.
AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)
ZnS(s) + 2HCl(aq) ZnCl2(aq) + H2S(g)
Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings
Chapter 9 Slide 30 of 37
Learning Check Classify the following reactions as
A) single replacement B) double replacement
Chapter 9 Slide 31 of 37
In a combustion reaction,
• A compound such as carbon reacts with oxygen, O2.
C(s) + O2(g) CO2(g)
CH4(g) + 2O2(g) CO2 (g) + 2H2O(g)
C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g)
• Fuels burned in oxygen produce CO2, H2O, and energy.
Combustion
Chapter 9 Slide 32 of 37
Learning Check
Balance the combustion equation
___C5H12 + ___O2 ___CO2 + ___H2O
Chapter 9 Slide 33 of 37
Summary of Reaction Types
Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings
Table 9.4
Chapter 9 Slide 34 of 37
Heat of Reaction
The heat of reaction,• Is the amount of heat absorbed or released
during a reaction at constant pressure.• Is the difference in the energy of the
reactants and the products.• Is shown as the symbol ΔH. ΔH = Hproducts − Hreactants
Chapter 9 Slide 35 of 37
Endothermic Reactions
In an endothermic reaction,
• Heat is absorbed.
• The sign of ΔH is +.
• The energy of the products is greater than the energy of the reactants.
• Heat is a reactant.
N2(g) + O2 (g) + 181 kJ 2NO(g)
ΔH = +181 kJ (heat added)
Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
Chapter 9 Slide 36 of 37
Exothermic Reactions
In an exothermic reaction,• Heat is released.• The sign of ΔH is -.• The energy of the products is less
than the energy of the reactants.
• Heat is a product.
C(s) + 2H2(g) CH4(g) + 75 kJ
ΔH = - 75 kJ (heat given off) Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings
Chapter 9 Slide 37 of 37
Learning Check
Identify each reaction as
1) exothermic or 2) endothermic.
A. N2 + 3H2 2NH3 + 92 kJ
B. CaCO3 + 556 kJ CaO + CO2
C. 2SO2 + O2 2SO3 + heat