1. Chemical Reactions
Chapter 10

2. Reactions and Equations
Section 9.1

3. Vocabulary
Review chemical change: a process involving one or more substances changing into a new substance New chemical reaction reactant product chemical equation coefficient Main Idea – Chemical reactions are represented by balanced chemical equations.

4. Chemical Reactions
The process by which one or more substances are rearranged to form different substances is called a chemical reaction.

5. Evidence of Chemical Reactions
Change in temperature
Heat absorbed or produced
endothermic or exothermic
Change in color
Light may be produced
Odor, gas, or bubbles may form
A solid may form (called a precipitate)

6. Representing Chemical Reactions
Chemists use statements called equations to represent chemical reactions.
Reactants are the starting substances.
Products are the substances formed in the reaction.
Reactants ® Products

7. Products
Reactants

8. In a chemical reaction
Atoms aren’t created or destroyed according to the
Law of Conservation of Mass
A reaction can be described several ways:
In a sentence every item is a word
Copper reacts with chlorine to form copper (II) chloride.
In a word equation some symbols used
Copper + chlorine ® copper (II) chloride
In a chemical equation only symbols used
Cu(s) + Cl2(g) ® CuCl2(s)

9. This table summarizes the symbols used in chemical equations.

10. Symbols in equations (aq) after the formula = aqueous solution
the arrow (→) separates the reactants from the products (arrow points to products)
Read as: yields or produces
The plus sign = “and”
(s) after the formula = solid: Fe(s)
(g) after the formula = gas: CO2(g)
(l) after the formula = liquid: H2O(l)
(aq) after the formula = aqueous solution
the substance is dissolved in water
Ex) NaCl(aq) is a salt water solution

11. Symbols used in equations
double arrow indicates a reversible reaction (more later)
shows that heat is supplied to the reaction
is used to indicate a catalyst is supplied (in this case, platinum is the catalyst) – “cat” means any catalyst.

12. What is a catalyst? More in a later chapter
A substance that speeds up a reaction, without being changed or used up by the reaction.
Enzymes are biological or protein catalysts in your body.
More in a later chapter

13. Representing Chemical Reactions
In word equations,
aluminum(s) + bromine(l) → aluminum bromide(s)
read as
“aluminum and bromine react to produce aluminum bromide”.
Skeleton equations use symbols and formulas to represent the reactants and products.
Al(s) + Br2(l) → AlBr3(s)
Skeleton equations lack information about how many total atoms are involved in the reaction.

14. Representing Chemical Reactions
A chemical equation is a statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction.

15. Example - Write a skeleton equation for:
Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas.
Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.

16. Now, read these equations:
Fe(s) + O2(g) ® Fe2O3(s)
Cu(s) + AgNO3(aq) ® Ag(s) + Cu(NO3)2(aq)
NO2(g) N2(g) + O2(g) Pt

17. Balancing Chemical Equations
This figure shows the balanced equation for the reaction between aluminum and bromine.

18. Balanced Chemical Equations
Atoms can’t be created or destroyed in an ordinary reaction:
All the atoms we start with we must end up with (meaning: balanced!)
A balanced equation has the same number of each element on both sides of the equation.

19. Balancing Chemical Equations
A coefficient in a chemical equation is the number written in front of a reactant or product, describing the lowest whole-number ratio of the amounts of all the reactants and products.

20. Balancing Chemical Equations

21. Balancing Chemical Equations

22. Balancing Chemical Equations

23. Balancing Chemical Equations
The most fundamental law in chemistry is the law of conservation of mass.
Balanced equations show this law.

24. Balancing Chemical Equations

25. Rules for balancing: Write a skeleton equation if not given it
Count the number of atoms of each type appearing on both sides
Balance the elements one at a time by adding coefficients (the numbers in front) where you need more - save balancing the H and O until LAST!
(hint: Save O until the very last – it will generally balance itself at this point)
Check to make sure it is balanced.

26. Never
Never change a subscript to balance an equation (You can only change coefficients)
H2O is a different compound than H2O2
Never put a coefficient in the middle of a formula; they must go only in the front
2NaCl is correct, but Na2Cl is not.

27. Practice Balancing Examples
_AgNO3 + _Cu ® _Cu(NO3)2 + _Ag
_Mg + _N2 ® _Mg3N2
_P + _O2 ® _P4O10
_Na + _H2O ® _H2 + _NaOH
_CH4 + _O2 ® _CO2 + _H2O 2 2 3 4 5 2 2 2 2 2

28. 10.1 Check
Which of the following is NOT a chemical reaction? A. a piece of wood burning B. a car rusting C. an ice cube melting into water D. red litmus paper turning blue

29. 10.1 Check
What is the coefficient of bromine in the equation 2Al(s) + 3Br2(l) → 2AlBr3(s)? A. 1 B. 2 C. 3 D. 6

30. Classifying Chemical Reactions
10.2

31. Vocabulary Review Main Idea New synthesis reaction
metal: an element that is a solid at room temperature, a good conductor of heat and electricity, and is generally shiny
Main Idea
There are four types of chemical reactions: synthesis, combustion, decomposition, and replacement reactions.
New
synthesis reaction
combustion reaction
decomposition reaction
single-replacement reaction
double-replacement reaction
precipitate

32. Types of Chemical Reactions
Chemists classify reactions in order to organize the many types.
There are probably millions of reactions.
Many of them can be classified in 4 or 5 categories

33. Synthesis Reaction
A synthesis reaction is a reaction in which two or more substances react to produce a single product
A + B → AB
When two elements react, the reaction is always a synthesis reaction.

34. Combustion Reactions
In a combustion reaction, oxygen combines with a substance and releases energy in the form of heat and light.
Example) Heated hydrogen reacts with oxygen to produce heat and water in a combustion reaction. This is also a synthesis reaction.

35. Combustion Reactions
Some combustion reactions are synthesis reactions, but not all of them.
For Example,
CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)

36. Decomposition Reactions
A decomposition reaction is one in which a single compound breaks down into two or more elements or new compounds.
AB → A + B
Decomposition reactions often require an energy source, such as heat, light, or electricity, to occur.

37. Replacement Reactions
A reaction in which the atoms of one element replace the atoms of another element in a compound is called a single replacement reaction.
A + BX → AX + B

38. Replacement Reactions
A metal will not always replace a metal in a compound dissolved in water because of differing reactivities.
An activity series can be used to predict if reactions will occur.

39. Replacement Reactions
Halogens frequently replace other halogens in replacement reactions.
Halogens also have different reactivities and do not always replace each other.

40. Replacement Reactions
Double replacement reactions occur when ions exchange between two compounds.
This figure shows a generic double replacement equation.

41. Replacement Reactions
The solid product produced during a chemical reaction in a solution is called a precipitate.
Beautiful precipates video:
Lead Iodide precipitate demo:

42. Replacement Reactions
All double replacement reactions produce one of these
water
a precipitate
a gas

43. Replacement Reactions
This table shows the steps
to write double replacement
reactions.

44. Predicting Products
This table summarizes different ways to predict the products of a chemical reaction.

45. 10.2 Check
Which of the following is NOT one of the four types of reactions? A. deconstructive B. synthesis C. single replacement D. double replacement

46. 10.2 Check
The following equation is what type of reaction? KCN(aq) + HBr(aq) → KBr(aq) + HCN(g) A. deconstructive B. synthesis C. single replacement D. double replacement

47. Reactions in Aqueous Solutions
10.3

48. Vocabulary
Review
solution: a uniform mixture that might contain solids, liquids, or gases
New
aqueous solution
solute
solvent
complete ionic equation
spectator ion
net ionic equation
Main Idea
Double-replacement reactions occur between substances in aqueous solutions and produce precipitates, water, or gases.

49. Aqueous Solutions
An aqueous solution contains one or more dissolved substances (called solutes) in water.
The solvent is the most plentiful substance in a solution.

50. Aqueous Solutions Water is always the solvent in an aqueous solution.
There are many possible solutes—sugar and alcohol are molecular compounds that exist as molecules in aqueous solutions.
Compounds that produce hydrogen ions in aqueous solutions are acids.

51. Aqueous Solutions
Ionic compounds (salts) can also be solutes in aqueous solutions.
When ionic compounds dissolve in water, their ions separate in a process called dissociation.

52. Types of Reactions in Aqueous Solutions
When two solutions that contain ions as solutes are combined, the ions might react.
If they react, it is always a double replacement reaction.
Three products can form:
Precipitates
water
gases.

53. Types of Reactions in Aqueous Solutions
Aqueous solutions of sodium hydroxide and copper(II) chloride react to form the precipitate copper(II) hydroxide.
2NaOH(aq) + CuCl2(aq) → 2NaCl(aq) + Cu(OH)2(s)
Ionic equations that show all of the particles in a solution as they actually exist are called complete ionic equations.
2Na+(aq) + 2OH–(aq) + Cu2+ (aq)+ 2Cl–(aq) → 2Na+(aq) + 2Cl–(aq) + Cu(OH)2(s)

54. Types of Reactions in Aqueous Solutions
Ions that do not participate in a reaction are called spectator ions and are not usually written in ionic equations.
Formulas that include only the particles that participate in reactions are called net ionic equations.
2OH–(aq) + Cu2+(aq) → Cu(OH)2(s)

55. Types of Reactions in Aqueous Solutions
Some reactions produce more water molecules.
No evidence of a chemical reaction is observable.
HBr(aq) + NaOH(aq) → H2O(l) + NaBr(aq)
Without spectator ions
H+(aq) + OH–(aq) → H2O(l).

56. Types of Reactions in Aqueous Solutions
Gases that are commonly produced are carbon dioxide, hydrogen cyanide, and hydrogen sulfide.
2HI(aq) + Li2S(aq) → H2S(g) + 2LiI(aq)

57. Types of Reactions in Aqueous Solutions
Another example is mixing vinegar and baking soda, which produces carbon dioxide gas.
HCl(aq) + NaHCO3(aq) → H2CO3(aq) + NaCl(aq)
H2CO3(aq) decomposes immediately.
H2CO3(aq) → H2O(l) + CO2(g)

58. Types of Reactions in Aqueous Solutions
Two reactions can be combined and represented by a single chemical reaction.

59. Types of Reactions in Aqueous Solutions
HCl(aq) + NaHCO3(aq) → H2CO3(aq) + NaCl(aq)
Reaction 2
H2CO3(aq) → H2O(l) + CO2(g)
Combined equation
HCl(aq) + NaHCO3(aq) + H2CO3(aq) →
H2CO3(aq) + NaCl(aq) + H2O(l) + CO2(g)
Overall equation
HCl(aq) + NaHCO3(aq) → H2O(l) + CO2(g) + NaCl(aq)

60. 10.3 Check
What is the solvent in an aqueous solution? A. hydrogen B. sodium ions C. water D. alcohol

61. 10.3 Check
An equation that includes only the particles that participate in a reaction is called: A. net ionic equation B. spectator ions C. complete ionic equation D. reduced ionic equation

62. Ch 10 Key Concepts
Some physical changes are evidence that indicate a chemical reaction has occurred.
Word equations and skeleton equations provide important information about a chemical reaction.
A chemical equation gives the identities and relative amounts of the reactants and products that are involved in a chemical reaction.
Balancing an equation involves adjusting the coefficients until the number of atoms of each element is equal on both sides of the equation.

63. Ch 10 Key Concepts
Classifying chemical reactions makes them easier to understand, remember, and recognize.
Activity series of metals and halogens can be used to predict if single-replacement reactions will occur.

64. Ch 10 Key Concepts
In aqueous solutions, the solvent is always water. There are many possible solutes.
Many molecular compounds form ions when they dissolve in water. When some ionic compounds dissolve in water, their ions separate.
When two aqueous solutions that contain ions as solutes are combined, the ions might react with one another. The solvent molecules do not usually react.
Reactions that occur in aqueous solutions are double-replacement reactions.

65. Ch 10 Key Concepts

66. Ch 10 Key Concepts