1. Chemical Reactions
Chemistry

2. Section 8.1 Describing Chemical Change
Objectives:
Write equations describing chemical reactions using appropriate symbols
Write balanced chemical equations when given the names or formulas of the reactants and products in a chemical reaction

3. Chemical Reaction
The process by which one or more substances are changed into one or more different substances.
Reactants → Products

4. Chemical Equation Describes chemical reactions
Uses symbols and formulas to identify relative amounts of reactants and products.

5. Indications of a Chemical Reaction
Evolution of heat and light.
Production of a gas.
Formation of a precipitate.
A solid that is formed from solutions in a chemical reaction.
Color change.

6. Characteristics of Chemical Equations
The equation must represent known facts.
All reactants and products must be identified.
The equation must contain the correct formulas for the reactants and products.
Sodium chloride = NaCl
Water = H2O
Carbon = C

7. Characteristics of Chemical Equations
The law of conservation of mass must be satisfied.
Atoms are neither created nor destroyed.
Coefficients are used to balance the number of atoms.

8. Word and Formula Equations
Word Equation – an equation in which the reactants and the products in a chemical reaction are represented by words.
Methane + oxygen → carbon dioxide + water
Has only descriptive (qualitative) meaning.
Formula Equation – represents the reactants and products of a chemical reaction by their symbols or formulas.
CH4 + O2 → CO2 + H2O
Also a qualitative statement.

9. Additional Symbols Used in Chemical Equations
↔ (reversible reaction)
↑ (gaseous product)
↓ (precipitate)
→ (yields)
(s) = solid
(l) = liquid
(g) = gas
(aq) = aqueous

10. Catalyst – A substance that changes the rate of a chemical reaction, but can be recovered unchanged.
Reversible Reaction – a chemical reaction in which the products re-form from the original reactants.

11. Significance of a Chemical Equation
1. The coefficients of a chemical reaction indicate relative, not absolute, amounts of reactants and products.
2. The relative masses of the reactants and products of a chemical reaction can be determined from the reaction’s coefficients.
3. The reverse reaction for a chemical equation has the same relative amounts of substances as the forward reaction.

12. Balancing Equations
The same number of atoms on each side of the yield symbol.
Only the coefficients can change to balance.
CH4 + O2 → CO2 + H2O
CH O2 → CO H2O

13. Balancing Chemical Equations
Balance the different types of atoms one at a time.
First balance the atoms of elements that are combined and that appear only once on each side of the equation.
Balance polyatomic ions that appear on both sides of the equation as single units.
Balance H atoms and O atoms after atoms of all other elements have been balanced.

14. Balanced Chemical Equation
Ex #1: Write a word and a balanced chemical equation for the following: hydrogen gas reacts with fluorine gas to produce hydrogen fluoride gas.
Word
hydrogen + fluorine → hydrogen fluoride
Balanced Chemical Equation
H2 (g) + F2 (g) → HF (g)
H2 (g) + F2 (g) → 2 HF (g)

15. Cu(s) + 2AgNO3 (aq) → Cu(NO3)2 (aq) + 2Ag(s)
Ex #2: Write a balanced chemical equation for the following: When solid copper reacts with aqueous silver nitrate, the products are aqueous copper (II) nitrate and solid silver.
Cu(s) + AgNO3 (aq) → Cu(NO3)2 (aq) + Ag(s)
Cu(s) + 2AgNO3 (aq) → Cu(NO3)2 (aq) + 2Ag(s)

16. Ex #3: Balance the following equations:
___AgNO3 + ___H2S → ___Ag2S + ___HNO3
___MnO2 + ___HCl → ___MnCl2 + ___H2O + ___ Cl2
___Zn(OH)2 + ___H3PO4 → ___Zn3(PO4)2 + ___H2O
___CO + ___Fe2O3 → ___Fe + ___CO2

17. Section 8.1 Describing Chemical Change
Did We Meet Our Objectives?
Write equations describing chemical reactions using appropriate symbols
Write balanced chemical equations when given the names or formulas of the reactants and products in a chemical reaction.

18. Types of Chemical Reactions
Section 8-2
Types of Chemical Reactions

19. Section 8.2 Types of Chemical Reactions
Objectives:
Identify a reaction as combination, decomposition, single-replacement, double-replacement, or combustion
Predict the products of combination, decomposition, single-replacement, double-replacement, and combustion reactions

20. Synthesis Reactions
Two or more substances combine to form a new compound.
Also known as composition reaction or combination reaction.
A + X → AX
A and X are elements, while AX is a compound.

21. Ex #4: Complete and balance the following combination reactions.
Be + O2 →
Cu + S →

22. Combination Reactions with Water
Some nonmetals oxides react with water to produce an acid.
SO2 + H2O → H2SO3

23. Ex #5: Complete and balance the following combination reaction.
SO3 + H2O →

24. Decomposition Reactions
A single compound undergoes a reaction that produces two or more simpler substances.
AX → A + X
AX is a compound and A and X are either elements or simpler compounds.
Most decomposition takes place only when energy in the form of electricity or heat is added.

25. Decomposition Continued……
Decomposition of Binary Compounds
Will produce elements.
2 H2O → 2 H2 + O2
The decomposition of a substance by an electric current is called electrolysis.
Oxides of less-active metals decompose into their elements when heated.
2 HgO → 2 Hg + O2

26. Ex #6: Complete and balance the following decomposition reactions.
HI →
PbO2 →

27. Single-Replacement Reactions
One element replaces a similar element in a compound.
Also known as displacement reaction.
Many take place in aqueous solutions.
A + BX → AX + B or
Y + BX → BY + X

28. Single-Replacement Reactions Continued……
Replacement of a Metal in a Compound by Another Metal
If the single metal is more reactive than the compound metal, the single metal will replace it.
2 Al + 3 Pb(NO3)2 → 3 Pb + 2 Al(NO3)3

29. Ex #7: Complete and balance the following single-replacement reactions.
Mg + Zn(NO3)2 →
Cl2 + NaBr →

30. Activity Series
A list of elements organized according to the ease with which the elements undergo certain chemical reactions.
For metals – greater activity means greater ease of loss of electrons.
For nonmetals – greater activity means greater ease of gain of electrons.

31. Ex #8: Use the activity series to predict whether each will react.
Zn(s) + H2O(l) → (at 50.0 °C)
No reaction
Sn(s) + O2(g) →
Yes, a reaction will occur
Cd(s) + Pb(NO3)2(aq) →
Cu(s) + HCl(aq) →

32. Double-Replacement Reactions
The ions of two compounds exchange places in an aqueous solution to form two new compounds. One of the new compounds is usually a precipitate, gaseous product, or water.
AX + BY → AY + BX

33. Double-Replacement Reactions Continued……..
Formation of a Precipitate
Cations and Anions form an insoluble compound.
Formation of a Gas
One of the products is an insoluble gas that bubbles out of the mixture.
Formation of Water
Usually an acid and a base will form a salt and water.

34. Ex #9: Complete and balance the following double displacement reactions.
BaCl2 + K2CO3 →
FeS + HCl →

35. Combustion Reactions
A substance combines with oxygen, releasing a large amount of energy in the form of light and heat.
Hydrocarbon + O2 → CO2 + H2O
CH4 + 2 O2 → CO2 + 2 H2O

36. Ex #10: Complete and balance the following combustion reactions.
C6H →
CH →
C11H →

38. Section 8.2 Types of Chemical Reactions
Did We Meet Our Objectives?
Identify a reaction as combination, decomposition, single-replacement, double-replacement, or combustion
Predict the products of combination, decomposition, single-replacement, double-replacement, and combustion reactions

39. Section 8.3 Reactions in Aqueous Solutions
Objectives:
Write and balance net ionic equations
Use solubility rules to predict the precipitate formed in double-replacement reactions

40. Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) → AgCl(s) + Na+(aq) + NO3-(aq)
Net Ionic Equations
Most ionic compounds dissociate (separate) into cations and anions when they dissolve in water.
A complete ionic equation is an equation that shows the dissolved ionic compounds as their free ions.
Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) → AgCl(s) + Na+(aq) + NO3-(aq)

41. Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) → AgCl(s) + Na+(aq) + NO3-(aq)
Net Ionic Equations
If you notice, there are some ions that are the same on both sides of the equation. These are called spectator ions. These ions are not directly involved in the reaction.
Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) → AgCl(s) + Na+(aq) + NO3-(aq)
Na+(aq) and NO3-(aq) are spectator ions for the above equation.

42. Net Ionic Equations
We can cancel the spectator ions in the following equation. The items left provide us with the net ionic equation, the equation that indicates only those particles that actually take part in the equation.
Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq) → AgCl(s) + Na+(aq) + NO3-(aq)
Ag+(aq) + Cl-(aq) → AgCl(s)

43. Ex #11: Write the balanced net ionic equation for the following.
Pb(ClO4)2(aq) + 2NaI(aq) → PbI2(s) + 2NaClO4(aq)
Complete Ionic Equation:
Pb(aq) + 2ClO4(aq) + 2Na(aq) + 2I(aq) → PbI2(s) + 2Na(aq) + 2ClO4(aq)
Spectator Ions:
2Na(aq) and 2ClO4(aq)
Net Ionic Equation:
Pb(aq) + 2I(aq) → PbI2(s)

44. Solubility Rules

45. Complete Ionic Equation:
Ex #12: Write a complete ionic equation and a net ionic equation for the reaction of aqueous solutions of iron (III) nitrate and sodium hydroxide.
Fe(NO3)3 + NaOH → NaNO3 + Fe(OH)3
Fe(NO3)3 + 3NaOH → 3NaNO3 + Fe(OH)3
Fe(NO3)3(aq) + 3NaOH(aq) → 3NaNO3(aq) + Fe(OH)3(s)
Complete Ionic Equation:
Fe(aq)3+ + 3NO3-(aq) + 3Na(aq) + 3OH-(aq) → 3Na(aq) + 3NO3-(aq) + Fe(OH)3(s)
Net Ionic Equation:
Fe(aq)3+ + 3OH-(aq) → Fe(OH)3(s)

46. Section 8.3 Reactions in Aqueous Solutions
Did We Meet Our Objectives?
Write and balance net ionic equations
Use solubility rules to predict the precipitate formed in double-replacement reactions