1. Chapter 6
Chemical Reactions

2. 6.1 Types of Chemical Reactions: Synthesis
Synthesis reactions are also known as formation reactions.
Two or more reactants (usually elements) join to form a compound.
A + B  AB where A and B represent elements

3. The elements may form ionic compounds, like the following:
Sodium metal and chlorine gas combine to form sodium chloride.
2Na + Cl2  2NaCl
Magnesium metal reacts with oxygen gas to form magnesium oxide.
2Mg + O2  2MgO
Sodium added to chlorine gas

4. Or the elements may form covalent compounds, like the following:
Nitrogen gas and oxygen gas join to form dinitrogen monoxide.
2N2 + O2  2N2O

5. An Analogy for Synthesis
Guy meets girl, they become a couple ;)
(or, assuming that in this example that the girl represents a metal and the guy represents a non-metal, it could be a covalent bond with two guys  ) + 

7. Types of Chemical Reactions: Decomposition
Decomposition reactions are the opposite of synthesis reactions.
A compounds breaks down into two or more products (often elements).
AB  A + B where A and B represent elements

8. Ionic compounds may decompose to produce elements, like the following:
Table salt, sodium chloride, can be broken down into sodium metal and chlorine gas by melting salt at 800ºC and running electricity through it.
2NaCl  2Na + Cl2

9. Or covalent compounds may decompose into elements, or diatoms (HOBrFINCl) like the following:
By running electricity through water, the
water molecules decompose into
hydrogen and oxygen gases.
2H2O  2H2 + O2

10. An Analogy for Decomposition
Couple breaks up   +

12. Types of Chemical Reactions: Single Replacement
Single replacement reactions replace one element from a compound with a separate element added as a reactant.
A compound and an element react, and the element switches places with part of the original compound.
B + AX  A + BX where A and B are metals, or
Y + AX  X + AY where X and Y are non-metal

13. Replacement of a metal:
Aluminum foil in a solution of copper(II) chloride produces solid copper and aluminum chloride.
2Al + 3CuCl2  3Cu + 2AlCl3
Replacement of a non-metal:
When fluorine is bubbled through a sodium iodide solution, iodine and sodium fluoride are produced.
F2 + 2NaI  I2 + 2NaF

14. An Analogy for Single Replacement Reactions
1 partner decides to ditch their current partner for someone new :O

16. Types of Chemical Reactions: Double Replacement
Double replacement reactions swap elements between two compounds reacting together to form two new compounds.
Two compounds react, with elements switching places between the original compounds.
Two solutions react to form a precipitate (ppt, solid) and another solution
Ionic solution + ionic solution  ionic solution + ionic solid
AB + CD  AD + CB
See page 262

17. When potassium chromate and silver nitrate react, they form a red precipitate, silver chromate, in a solution of potassium nitrate.
K2CrO4 + 2AgNO3  Ag2CrO4 + 2KNO3
silver chromate

18. An Analogy for Double Replacement
Start with two couples, and they both switch partners
Swingers! :P +  +
(c) McGraw Hill Ryerson 2007

20. Types of Chemical Reactions: Neutralization (Acid-Base Reactions)
Neutralization reactions occur when an acid (most compounds starting with H) and a base (most compounds ending in OH, or beginning with NH4) react to form a salt and water.
Acid + base  salt + water
HX + MOH  MX + H2O where X is a non-metal ion and M is a metal ion

21. Sulfuric acid is used to neutralize calcium hydroxide:
H2SO4 + Ca(OH) 2  CaSO4 + 2H2O
Phosphoric acid helps to neutralize the compounds that cause rust, such as iron(II) hydroxide.
2H3PO4 + 3Fe(OH)2  Fe3(PO4)2 + 6H2O
Neutralization is just a special case of a double replacement reaction

23. Types of Chemical Reactions: Combustion
Combustion reactions occur when a compound or element react with oxygen to release energy and produce an oxide.
Also sometimes referred to as hydrocarbon combustion.
CXHY + O2  CO2 + H2O where X and Y represent whole numbers

24. Natural gas (methane) is burned in furnaces to heat homes.
CH4 + 2O2  CO2 + 2H2O
An acetylene torch is used to weld metals together.
2C2H2 + 5O2  4CO2 + 2H2O
Carbohydrates like glucose combine with oxygen in our body to release energy.
C6H12O6 + 6O2  6CO2 + 6H2O

26. Types of Chemical Reactions: Summary of Types

27. To Do:
Chp 6.1 worksheets

28. 6.2 Factors Affecting the Rate of Chemical Reactions

29. 6.2 Factors Affecting the Rate of Chemical Reactions
Often, controlling the rate of a chemical reaction is as important as having the reaction occur in the first place.
Many factors can determine the rate at which a chemical reaction occurs.
A bicycle chain slowly rusts.

30. To make a reaction happen quickly:
Increase the temperature where the reaction occurs.
Increase the concentration of reactants.
Increase the amount of surface area that reacts.
Add a catalyst or remove an inhibitor.

31. To make a reaction happen slowly:
Decrease the temperature where the reaction occurs.
Decrease the concentration of reactants.
Decrease the amount of surface area that reacts.
Remove a catalyst or add an inhibitor.

32. Temperature Temperature is the average kinetic energy of molecules.
The more energy molecules have, the higher the temperature.
When molecules have more energy, they move around more, bump into other molecules more, and collide, and therefore react faster.

33. The rate of reaction changes with the temperature.
Higher temperature = faster reaction rate, and vice versa.
Sometimes we want slower reactions (we use a fridge to prevent spoilage).
Sometimes we want faster reactions (we cook food to speed up the production of new molecules).
The chemical reaction rate is higher in hot water than in cold water.

35. Concentration
Concentration refers to how many molecules of a substance exist in a certain volume.
Concentration is how much solute is dissolved in solution.
Concentration is measured in mass per unit volume (g/L).

36. Usually, the higher the concentration of
reactants, the faster the reaction occurs.
Since there are more molecules per unit volume in high concentrations, there are more opportunities for molecules to collide and react.

37. Changing the concentration of O2 changes the intensity of flames.
A splint of wood glows brighter in highly concentrated oxygen than in normal air with a lower concentration of oxygen.
Changing the concentration of O2 changes the intensity of flames.

38. Surface Area
Chemical reactions occur when and where atoms and compounds collide.
The more atoms and molecules there are to collide, the higher the reaction rate.

39. Increasing surface area increases the rate of reaction.
Surface area can be increased by creating smaller pieces.
A powdered substance has far more surface area than one large chunk.
The increase in surface area must also be exposed for reaction; a powder only reacts more quickly if it is spread into the air instead of lying on a pan.

40. Steel wool (on the right) is made up of small strands of steel, and therefore has much more surface area than an equivalent amount of solid steel.

41. Catalysts
Sometimes, increasing the temperature or concentration is not a desirable method to increase reaction rate.
Changing these two variables may be impractical or dangerous.
A catalyst is a chemical that allows a reaction to occur more quickly without actually participating in the reaction itself.

42. The catalyst speeds up the reaction rate but does not
get used up as a reactant.
Catalysts often lower the amount of energy necessary
to break the bonds in the reactants.

44. Salivary amylase increases the digestion of starches.
Enzymes are an example of biological catalysts.
Saliva has enzymes that help speed the breakdown of starches when they enter the mouth.
Salivary amylase increases the digestion of starches.

45. A catalytic converter is a device installed in cars to decrease pollution.
Car exhaust passes through the catalytic converter before leaving the car.
A catalytic converter.

46. Catalysts found in the honeycomb-shaped filters in the converter help to change many of the pollutants into less harmful substances.
Poisonous carbon monoxide is changed into CO2.
Hydrocarbons are converted into CO2 and H2O.
Nitrogen oxides are changed into N2 and O2.
2N2O3  2N2 + 3O2

47. Inhibitors are substances that slow down
a reaction by getting in way of the molecules
when they’re trying to react

48. To Do:
Chapter 6.2 Workbook (handout) Review Questions