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 O 2 form rust (Fe 2 O 3 )

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) O 2 (g) CO 2 (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 H 2 + O 2  H 2 O A Chemical Equation must also be balanced. 2H 2 + O 2 --> 2H 2 O

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 Al 2 S 3 Not Balanced How many atoms of Al and S are on each side of the equation? coefficients Al + S Al 2 S 3 _ Al = _ Al _ S = _ S

Chapter 9 Slide 15 of 37 Learning Check State the number of atoms of each element on the reactant and on the product sides of the equations: P 4 (s) + 6 Br 2 (l) → 4 PBr 3 (g)

Chapter 9 Slide 16 of 37 Learning Check State the number of atoms of each element on the reactant and on the product sides of the equations: 2Al(s) + Fe 2 O 3 (s) → 2Fe(s) + Al 2 O 3 (s)

Chapter 9 Slide 17 of 37 Check the balance of atoms in the following: Fe 3 O 4 (s) + 4H 2 (g) 3Fe(s) + 4H 2 O(l) Learning Check

Chapter 9 Slide 18 of 37 Learning Check Determine if each equation is balanced or not. Na(s) + N 2 (g) → NaN 3 (s) C 2 H 4 (g) + H 2 O(l) → C 2 H 5 OH(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 CH 4 + O 2  CO 2 + H 2 O 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 C 2 H 6 + O 2  CO 2 + H 2 O C 3 H 6 + O 2  CO 2 + H 2 O NH 3 + O 2  NO + H 2 O

Chapter 9 Slide 22 of 37 And more practice…. B 2 H 6 + H 2 O  H 3 BO 3 + H 2 C 3 H 8 O + O 2  CO 2 + H 2 O

Chapter 9 Slide 23 of 37 Balancing with Polyatomic Ions MgCl 2 (aq) + Na 3 PO 4 (aq) NaCl(aq) + Mg 3 (PO 4 ) 2 (s) HINT: Balance PO 4 3- 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) + O 2 (g) 2MgO(s) 2Na(s) + Cl 2 (g)2NaCl(s) SO 3 (g) + H 2 O(l)H 2 SO 4 (aq) AB AB

Chapter 9 Slide 26 of 37 Decomposition In a decomposition reaction, One substance splits into two or more simpler substances. 2HgO(s) 2Hg(l) + O 2 (g) 2KClO 3 (s) 2KCl(s) + 3O 2 (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 Replacement In a single replacement reaction, One element takes the place of a different element in a reacting compound. Zn(s) + 2HCl(aq) ZnCl 2 (aq) + H 2 (g) Fe(s) + CuSO 4 (aq) FeSO 4 (aq) + Cu(s) Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Chapter 9 Slide 29 of 37 Double Replacement In a double replacement reaction, Two elements in the reactants exchange places. AgNO 3 (aq) + NaCl(aq)AgCl(s) + NaNO 3 (aq) ZnS(s) + 2HCl(aq)ZnCl 2 (aq) + H 2 S(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, O 2. C(s) + O 2 (g)CO 2 (g) CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) C 3 H 8 (g) + 5O 2 (g) 3CO 2 (g) + 4H 2 O(g) Fuels burned in oxygen produce CO 2, H 2 O, and energy. Combustion

Chapter 9 Slide 32 of 37 Learning Check Balance the combustion equation ___C 5 H 12 + ___O 2 ___CO 2 + ___H 2 O

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 = H products − H reactants

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. N 2 (g) + O 2 (g) 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) + 2H 2 (g) CH 4 (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. N 2 + 3H 2 2NH kJ B. CaCO kJCaO + CO 2 C. 2SO 2 + O 2 2SO 3 + heat