Chapter 11

1. Chapter 11 Chemical Reactions

2. Section 1 Describing Chemical Reactions

3. Section 1 Learning Targets 11.1.1 – I can describe how to write a word equation. 11.1.2 – I can describe how to write a skeleton equation. 11.1.3 – I can describe the steps for writing a balanced chemical equation.

4. Writing chemical equations • In a chemical reaction, one or more reactants change into one or more products.

5. Word equations • To write a word equation, write the names of the reactants to the left of the arrow separated by plus signs; write the names of the products to the right of the arrow, also separated by plus signs.

6. iron + oxygen → iron (III) oxide • Iron plus oxygen yields iron (III) oxide. • Iron plus oxygen reacts to form iron (III) oxide.

7. Chemical equations • Chemical equation – a representation of a chemical reaction: the formulas of the reactants (on the left) are connected by an arrow with the formulas of the products (on the right).

8. Skeleton equation – is a chemical equation that does not indicate the relative amounts of the reactants and products. • Catalyst – a substance that speeds up the reaction but is not used up in the reaction.

9. With out catalyst With catalyst

10. Write the formulas of the reactants to the left of the yield sign (arrow) and the formulas for the products to the right. • Fe(s) + O2(g) → Fe2O3(s)

12. Balancing chemical equations • Coefficients – small whole numbers that are placed in front of the formulas in an equation in order to balance it.

13. Balanced equation – a chemical equation in which each side of the equation has the same number of atoms of each element and mass is conserved.

15. To write a balanced chemical equation, first write the skeleton equation. • Then use coefficients to balance the equation so that it obeys the law of conservation of mass.

18. Examples • _____ H2(g) + _____ O2(g) → _____ H2O(l)

19. Examples • ___ AgNO3 + ___ H2S → ____ Ag2S + ___ HNO3

20. Examples • ___ Zn(OH)2 + ___ H3PO4 → ___ Zn3(PO4)2 + ___ H2O

21. Section 2 Types of Chemical Reactions

22. Section 2 learning targets 11.2.1 – I can describe the five general types of reactions. 11.2.2 – I can predict the products of the five general types of reactions.

23. Classifying Reactions • The five general types of reactions are combination, decomposition, single-replacement, double-replacement, and combustion. Types of Chemical Reactions Video

24. Combination reactions • Combination reaction – chemical change in which two or more substances react to form a single new substance. • 2Mg(s) + O2(g) → 2MgO(s)

26. When a Group A metal and a nonmetal react the product is an ionic compound with the metal and nonmetal. • 2K(s) + Cl2(g) → 2KCl(s)

27. When two nonmetals react more than one product is possible. • S(s) + O2(g) → SO2(g) sulfur dioxide • 2S(s) + 3O2(g) → 2SO3(g) sulfur trioxide

28. Same with a transition metal and a nonmetal. • Fe(s) + S(s) → FeS(s) iron (II) sulfide • 2Fe(s) + 3S(s) → Fe2S3(s) iron (III) sulfide

29. Example: • Write and balance the equation for the formation of magnesium nitride (Mg3N2) from its elements. • HINT: there are 7 diatomic elements: H2, N2, O2, F2, Cl2, Br2, and I2. (BrINClHOF)

30. Decomposition reactions • Decomposition reaction – a chemical change in which a single compound breaks down into two or more simpler products. • 2HgO(s) → 2Hg(l) + O2(g)

32. Example: • Complete and balance this decomposition reaction: HI → _____________________________________

33. Single-replacement reaction • Single-replacement reaction – a chemical change in which one element replaces a second element in a compound.

35. Activity series – lists metals in order of decreasing activity. • Tells if one metal will replace another during a reaction. • 2K(s) + 2H2O(l) → 2KOH(aq) + H2(g) • Br2(aq) + NaCl(aq) → no reaction

37. The Halogens are a reactivity series themselves: • As you go down the group the reactivity decreases so anything on top will replace anything lower in that group.

38. Example: • Complete the equation for these single replacement reactions and balance each. • Fe(s) + Pb(NO3)2(aq) → ___________________ • Cl2(aq) + NaI(aq) → ______________________

39. Double-replacement reactions • Double-replacement reaction – a chemical change involving an exchange of positive ions between two compounds.

41. In double-replacement reactions one or more is probably true. • One of the products is only slightly soluble and precipitates from solution. • Na2S(aq) + Cd(NO3)2(aq) → CdS(s) + 2NaNO3(aq)

42. One of the products is a gas. • 2NaCN(aq) + H2SO4(aq) → 2HCN(g) + Na2SO4(aq)

43. One product is a molecular compound such as water. • Ca(OH)2(aq) + 2HCl(aq) → CaCl2(aq) + H2O(l)

44. Example: • Write a balanced equation for each reaction: • NaOH(aq) + Fe(NO3)3(aq) → ______________ [iron(III)hydroxide is a precipitate] • H2SO4(aq) + Al(OH)3(aq) → ________________

45. Combustion reactions • Combustion reaction – a chemical change in which an element or a compound reacts with oxygen, often producing energy in the form of heat and light.

47. One reactant is always oxygen and the other is usually a hydrocarbon. • 2C8H18(l) + 25O2(g) → 16CO2(g) + 18H2O(l)

48. Complete combustion happens when the supply of oxygen is unlimited. • Incomplete combustion happens when oxygen is limited.

49. Other elements/compounds can react with oxygen but those reactions are usually considered to be combination reactions.

50. Example: • Write a balanced equation for the complete combustion for each compound. • Formic acid (HCOOH) • Heptane (C7H16)