4. Objectives Apply the law of conservation of Mass to all chemical reactions Identify the parts of a chemical reaction Identify and write balanced equations for all types of inorganic reactions. Given the reactants, predict the products for a variety of inorganic chemical reactions

6. The Meaning of a Chemical Equation Chemical equations give information in two major areas. First, they tell us what substances are reacting (those being used up) and what substances are products (those being made). Second, the coefficients of a balanced equation tell us in what ratio the substances react or are produced. Chemical equations give information in two major areas. First, they tell us what substances are reacting (those being used up) and what substances are products (those being made). Second, the coefficients of a balanced equation tell us in what ratio the substances react or are produced.

7. The Meaning of a Chemical Equation This last point regarding reaction ratios has practical consequences whenever chemicals react. For example, the large middle tank of the space shuttle actually has two smaller tanks in it - one holding liquid oxygen and the other holding liquid hydrogen. The tank with the hydrogen holds twice as much as the oxygen-holding tank. ………………Why?

8. The Meaning of a Chemical Equation Answer - hydrogen and oxygen always react in a 2:1 ratio. For any oxygen used by the shuttle, twice as much hydrogen is needed. If the two tanks were equal sizes, the hydrogen tank would run dry when the oxygen tank was still half-filled..

10. The Meaning of a Chemical Equation The reactants are on the left side of a chemical equation and the products are on the right side. However, you might ask, "On the left and right side of what?" Answer - the arrow, (which means Yields or produces). The reactants are on the left side of a chemical equation and the products are on the right side. However, you might ask, "On the left and right side of what?" Answer - the arrow, (which means Yields or produces).

11. The Meaning of a Chemical Equation 2 H 2 + O 2 ---> 2 H 2 O On the left side are the reactants - hydrogen and oxygen. We will ignore the two in front of the hydrogen for a moment. On the right side is the product - water. For now, we will ignore the two in front of the water, but we will soon return to it. 2 H 2 + O 2 ---> 2 H 2 O On the left side are the reactants - hydrogen and oxygen. We will ignore the two in front of the hydrogen for a moment. On the right side is the product - water. For now, we will ignore the two in front of the water, but we will soon return to it.

12. The Meaning of a Chemical Equation Please be aware that there can be one, two, three, or more substances on either side of the arrow, as in this more complex equation: Ca(H 2 PO 4 ) 2 + CaSO 4 + HF ---> Ca 10 F 2 (PO 4 ) 6 + H 2 SO 4 Typically the arrow is replaced with produces" or "yields" when the equation is said out loud. Please be aware that there can be one, two, three, or more substances on either side of the arrow, as in this more complex equation: Ca(H 2 PO 4 ) 2 + CaSO 4 + HF ---> Ca 10 F 2 (PO 4 ) 6 + H 2 SO 4 Typically the arrow is replaced with produces" or "yields" when the equation is said out loud.

13. The Meaning of a Chemical Equation Coefficients are the numbers in front of the formulas. Here is the example equation again: 2 H 2 + O 2 ---> 2 H 2 O Note the presence of a two in front of the hydrogen and also the water. These are called the coefficients. Coefficients are the numbers in front of the formulas. Here is the example equation again: 2 H 2 + O 2 ---> 2 H 2 O Note the presence of a two in front of the hydrogen and also the water. These are called the coefficients.

14. The Meaning of a Chemical Equation These numbers give two very important pieces of information about the equation. You must understand both in order to read and to use chemical equations successfully.

15. The Meaning of a Chemical Equation First: The coefficients give the number of molecules involved in the reaction. In the example reaction, two molecules of hydrogen react with one molecule of oxygen and produce two molecules of water. 2 H 2 + O 2 ---> 2 H 2 O

16. The Meaning of a Chemical Equation Second: The coefficients give the number of moles of each substance involved in the reaction. In the example reaction, two moles of hydrogen react with one mole of oxygen and produce two moles of water. 2 H 2 + O 2 ---> 2 H 2 O 1 1

17. The Meaning of a Chemical Equation Identify the reactants, the products and the coefficients of these equations: 1) Zn + 2 HCl ---> ZnCl 2 + H 2 2) 2 KClO 3 ---> 2 KCl + 3 O 2 3) S 8 + 24 F 2 ---> 8 SF 6 4) 4 Fe + 3 O 2 ---> 2 Fe 2 O 3 5) 2 C 2 H 6 + 7 O 2 ---> 4 CO 2 + 6 H 2 O

18. The Meaning of a Chemical Equation You know a chemical reaction takes place if one or more of these occur: 1. Color changes - Different combinations of molecules reflect light differently. A color change indicates a change in molecules. 2. Heat content changes - In all chemical reactions, the heat content of the reactants and the content of the products is never the same. Sometimes the difference is great and can be easily detected; at other times the difference is slight and is more difficult to detect. You know a chemical reaction takes place if one or more of these occur: 1. Color changes - Different combinations of molecules reflect light differently. A color change indicates a change in molecules. 2. Heat content changes - In all chemical reactions, the heat content of the reactants and the content of the products is never the same. Sometimes the difference is great and can be easily detected; at other times the difference is slight and is more difficult to detect.

19. The Meaning of a Chemical Equation You know a chemical reaction takes place if one or more of these occur (cont.): 3.A gas is produced - Whenever a gaseous product forms in a liquid solution, bubbles can be seen. A colorless gas produced in a reaction of solids is much harder to detect. 4.A precipitate forms - Precipitates are insoluble products formed by a reaction taking place in a liquid solution. Thi insoluble product will eventually settle to the bottom, bu might immediately appear by turning the clear solution cloudy. You know a chemical reaction takes place if one or more of these occur (cont.): 3.A gas is produced - Whenever a gaseous product forms in a liquid solution, bubbles can be seen. A colorless gas produced in a reaction of solids is much harder to detect. 4.A precipitate forms - Precipitates are insoluble products formed by a reaction taking place in a liquid solution. Thi insoluble product will eventually settle to the bottom, bu might immediately appear by turning the clear solution cloudy.

20. Reaction Types: Synthesis Also called, Direct Combination That means that two pieces join together to produce one, a more complex compound. These pieces can be elements or simpler compounds. Complex simply means that the product compound has more atoms than the reactant molecules. Usually!! Written using generic symbols, it is usually shown as: A + B ---> AB That means that two pieces join together to produce one, a more complex compound. These pieces can be elements or simpler compounds. Complex simply means that the product compound has more atoms than the reactant molecules. Usually!! Written using generic symbols, it is usually shown as: A + B ---> AB

21. Reaction Types: Synthesis These are some examples: Mg + O 2 ---> Please note that none of the following examples are balanced H 2 + O 2 ---> K + Cl 2 ---> Fe + O 2 ---> MgO H2OH2O H2OH2O KCl Fe 2 O 3

22. Reaction Types: Synthesis Synthesis can also be two compounds making a more complex compound (or a compound and an element joining together) as in these examples: CaO + CO 2 ---> Na 2 O + CO 2 ---> KCl + O 2 ---> CaCO 3 Na 2 CO 3 KClO 3

23. Reaction Types: Synthesis Notice how, in every case so far, there is only one substance on the right-hand (product) side. This is not always the case in a synthesis reaction. Sometimes there will be two products. Here's an example: CO 2 + H 2 O ---> C 6 H 12 O 6 + O 2

24. Reaction Types: Synthesis (also called Direct Combination) Synthesis reactions are the reverse of decomposition, and these rules apply: 1) Direct union of two elements will produce a binary compound. 2) Metallic oxides and carbon dioxide react to produce metallic carbonates. 3) Binary salts and oxygen react to produce a metallic halogenate.

25. Halogenate Defined A halogenate is any halogen (Family 7A element, not At ) that is combined in a polyatomic ion with 3 oxygen atoms ClO 3 -1 FO 3 -1 BrO 3 -1 IO 3 -1

26. Reaction Types: Decomposition During decomposition, one compound splits apart into two or more pieces. These pieces can be elements or simpler compounds AB ---> A + B Written using generic symbols, it is usually shown as:

27. Reaction Types: Decomposition The above illustration only works for splitting apart into elements, like these examples. AB ---> A + B HgO ---> MgCl 2 ---> FeS ---> Hg + O 2 H 2 O ---> H 2 + O 2 Mg + Cl 2 Fe + S

28. Reaction Types: Decomposition Decomposition can also split one compound into two simpler compounds (or a compound and an element) as in these examples: CaCO 3 ---> Na 2 CO 3 ---> KClO 3 ---> Ba(ClO 3 ) 2 ---> Notice there is only one substance on the left-hand (reactant) side. This is always the case in a decomposition reaction. CaO + CO 2 Na 2 O + CO 2 KCl + O 2 BaCl 2 + O 2

29. Reaction Types: Decomposition You will have to recognize several rules for writing decomposition reaction, here are the first four: (yes, there's more!): 1) All binary compounds will break down into their elements 2) All metallic carbonates break down to the metallic oxide and carbon dioxide. 3. Metallic Halogenates will break down to a binary salt and oxygen.

30. Reaction Types: Decomposition Here is a 4 th rule: 4. An acid or base breaks down into the oxide of the metal (in the case of bases) or the oxide of the nonmetal (in the case of acids) plus water.

31. Reaction Types: Decomposition Try these examples applying the 4 rules on the previous slides: 1) NaClO 3 ---> NaCl + O 2 2) Li 2 CO 3 ---> Li 2 O + CO 2 3) KOH ---> K 2 O + H 2 O 4) NaCl ---> Na + Cl 2

32. Reaction Types: Decomposition using synthesis Here is one more rule for writing decomposition reactions: CaO + H 2 O ---> Na 2 O + H 2 O ---> N 2 O 5 + H 2 O ---> P 2 O 5 + H 2 O ---> The first two examples show metallic oxides and the last two nonmetallic oxides. In the first 2 examples, the oxide plus water will produce a base (in the case of the metallic oxide) or an acid (in the case of the nonmetallic oxide). Ca(OH) 2 NaOH HNO 3 H 3 PO 4

33. Reaction Types: Single Replacement During single replacement, one element replaces another element in a compound. There are two different possibilities: 1. One cation replaces another. Written using generic symbols, it is: AX + Y ---> YX + A Element Y has replaced A (in the compound AX) to form a new compound YX and the free element A. Remember that A and Y are both cations (+) in this example.

34. Reaction Types: Single Replacement Here are 2 examples: Cu + AgNO 3 ---> Element Cu has replaced Ag (in the compound AgNO 3 ) to form a new compound Cu(NO 3 ) 2 and the free element Ag. Remember that Cu and Agare both cations (+) in this example. Fe + Cu(NO 3 ) 2 ---> Ag + Cu(NO 3 ) 2 Fe(NO 3 ) 3 + Cu

35. Reaction Types: Single Replacement Here is possibility #2 2. One anion replaces another. Written using generic symbols, it is: A + XY ---> XA + Y Element A has replaced Y (in the compound XY) to form a new compound XA and the free element Y. Remember that A and Y are both anions (-) in this example.

36. Reaction Types: Single Replacement Here are 2 examples: Cl 2 + NaBr ---> In single replacement, one reactant is always a single element. It does not matter if the element is written first or second on the reactant side. The other reactant will be a compound. Br 2 + KI ---> NaCl + Br 2 KBr + I 2

37. Reaction Types: Single Replacement You may ask, “How do you know if one element will replace another or not????” Refer to a table called the Activity Series. Refer to page 295 in your textbook. This table lists metals in the order of their ability to react. The most reactive element (Li), is at the top, and the least reactive metal (Au), is at the bottom.

38. Reaction Types: Single Replacement Refer to a table called the Activity Series. If a single metal element is located above the cation of a compound it is reacting with, the single element will replace the cation, forming a new compound. Li + NaCl ---> Since Li is higher on the “A.S.” than Na, it will replace it and form a new compound, LiCl. LiCl + Na

39. Reaction Types: Single Replacement Try these 2 examples Cl 2 + NaBr ---> In single replacement, one reactant is always a single element. It does not matter if the element is written first or second on the reactant side. The other reactant will be a compound. Br 2 + KI ---> NaCl + Br 2 KBr + I 2

40. Reaction Types: Single Replacement Try these 2 examples Cl 2 + NaBr ---> When dealing with anions, like chlorine and Bromine, the element higher in the family (higher electronegativity), will replace any anion below it. Br 2 + KI ---> NaCl + Br 2 KBr + I 2

41. Reaction Types: Double Replacement During double replacement, the cations and anions of two different compounds switch places. Written using generic symbols, it is: AB + XY ---> AY + XB A and X are the cations (+ ions) in this example, with B and Y being the anions (- ions). During double replacement, the cations and anions of two different compounds switch places. Written using generic symbols, it is: AB + XY ---> AY + XB A and X are the cations (+ ions) in this example, with B and Y being the anions (- ions).

42. Reaction Types: Double Replacement KOH + H 2 SO 4 -  FeCl 3 + H 6 S (aq) Na 2 SO 4 + HCl (aq) AgNO 3 + NaCl ---> K 2 SO 4 + H 2 O Fe 2 S + HCl (aq) ---> NaCl + H 2 SO 4 ---> AgCl + NaNO 3

43. Reaction Types: Double Replacement These three are also examples of double replacement, but there is something special about them: CaCO 3 + HCl (aq) ---> K 2 SO 3 + HNO 3 ---> NH 4 Cl + NaOH ---> CaCl 2 + CO 2 + H 2 O KNO 3 + SO 2 + H 2 O NaCl + NH 3 + H 2 O

44. Reaction Types: Double Replacement Whenever H 2 CO 3, H 2 SO 3, or NH 4 OH is a product formula, the correct technique is to write the products as done in the examples. Don't forget that! CaCl 2 + CO 2 + H 2 O CaCO 3 + HCl ---> With this in mind the following example would be incorrect: Decompose the H 2 CO 3 to CO 2 & H 2 O (below): CaCl 2 + H 2 CO 3 CaCO 3 + HCl --->

45. Reaction Types: Double Replacement Try these examples: 1) Ca(OH) 2 + HCl (aq) --> CaCl 2 + H 2 O 2) Al(NO 3 ) 3 + H 2 SO 4 (aq) --> Al 2 (SO 4 ) 3 + HNO 3 3) Pb(NO 3 ) 2 + K 2 S ---> PbS + KNO 3 4) Pb(NO 3 ) 2 + CuSO 4 ---> PbSO 4 + Cu(NO 3 ) 2

46. Reaction Types: Combustion Combustion, at its most general, can mean the reaction of oxygen gas (O 2 ) with anything. A common synonym for combustion is burn. Combustion, at its most general, can mean the reaction of oxygen gas (O 2 ) with anything. A common synonym for combustion is burn. Written using generic symbols, it is usually shown as: C x H y + O 2 ---> CO 2 + H 2 O Written using generic symbols, it is usually shown as: C x H y + O 2 ---> CO 2 + H 2 O

47. Reaction Types: Combustion Try some examples: CH 4 + O 2 ---> CO 2 + H 2 O C 2 H 6 + O 2 ---> CO 2 + H 2 O C 6 H 12 O 6 + O 2 ---> CO 2 + H 2 O C 2 H 5 OH + O 2 ---> CO 2 + H 2 O

48. Reaction Types: Combustion If the reactants contain the element Nitrogen, the following results will be obtained: C 21 H 24 N 2 O 4 + O 2 ---> C 2 H 5 SH + O 2 ---> If the reactants contain the element sulfur, the following results will be obtained: CO 2 + H 2 O + NO 2 CO 2 + H 2 O + SO 2

51. Balancing Reactions Chemical equations usually do not come already balanced. This must be done before the equation can be used in a chemically meaningful way. A balanced equation has equal numbers of each type of atom on each side of the equation.

52. Balancing Reactions The Law of conservation of Mass is the rationale for balancing a chemical equation. Therefore, we must finish our chemical reaction with as many atoms of each element as when we started. "Matter is neither created nor destroyed during a chemical change."

53. Balancing Reactions Here is the example equation: An unbalanced equation (sometimes also called a skeleton equation), has UNEQUAL numbers of at least one atom on each side of the arrow. H 2 + O 2 ---> H 2 O

54. Balancing Reactions Analyzing this reaction, you can count the following numbers of each type of atom on each side of the equation: H 2 + O 2 ---> H 2 O 2 Atoms H 2 Atoms O 2 Atoms H 1 Atom O

55. Balancing Reactions An equation is balanced by changing coefficients in a somewhat trial-and-error fashion. It is important to note that only the coefficients can be changed, NEVER a subscript. A coefficient is a whole number placed to the left of a formula indicating the number of molecules or “Moles” of that substance reacted or produced in the equation.

56. Balancing Reactions Using coefficients balance this equation: H 2 + O 2 ---> H 2 O 2 2 By placing a 2 in front of the H 2 O molecule we now have increased the oxygen quantity to 2. However in doing so, we have also increased the Hydrogen to 4, (2 x H 2 = 4H).

57. Balancing Reactions Since we increased both hydrogen and Oxygen on the product side of the reaction, we must make sure we make the atoms on the reactant side of the equation equal: H 2 + O 2 ---> 2H 2 O 2 2 If we add a coefficient 2 in front of the H 2 molecule on the left side of the equation, it’s balanced.

58. Balancing Reactions Balance this equation: H 2 + Cl 2 ---> HCl Balance this equation: H2 H2 + Cl 2 ---> HCl H 2 + Cl 2 ---> HCl 2 2

59. Balancing Reactions We will now begin learning to balance equations by using molecular models..