1. Chemical Reactions
(Chapter 13)
coefficients
reactants
products

2. Student Learning Objectives
Describe and predict types of chemical bonds
Utilize chemical equations to determine the amounts of reactants, products, and energy change
Characterize chemical bonds involving acids and bases
Analyze reactions involving oxygen and describe applications

3. How is a chemical equation balanced?
A chemical reaction is the process of forming new substances.
Atoms are combined to form molecules.
Molecules separate into atoms.
The chemical equation shows definite proportions of each substance. (same numbers of atoms on each side)
Al Br2  Al2Br6

4. Practice Pb + PbO2 + H2SO4  PbSO4 + H2O C3H8 + O2  CO2 + H2O
Al + HCl  AlCl3 + H2
BaO + H2O  Ba(OH)2

5. Moles, Grams, & Molecules
There are always x 1023 atoms or molecules in 1 mole of a substance.
Avogadro’s Number
Hydrogen & Water
6.022 x 1023 particles
mole

6. a) Gold b) NaCl c) Cu(NO3)2
Practice
Calculate the amount of grams and number of particles in one mole.
a) Gold b) NaCl c) Cu(NO3)2
Calculate the number of moles, and the number of molecules, in 2 grams of carbon dioxide.

7. More Practice
How many grams of each reactant are needed and how many grams of product are produced in the reaction?
Al + Br2  Al2Br3

8. What are exothermic and endothermic reactions?
The amount of chemical potential energy may change during a chemical reaction.
Exothermic
Endothermic
Energy released
Energy absorbed
Reactants → higher PE
Products → higher PE

9. University of Florida Department of Chemistry
Activation Energy
A spike of energy is needed to break existing bonds.
illustrated by
University of Florida Department of Chemistry
Image: BBC

10. Image Credit: Socratic.org

11. Activation Energy with a Catalyst

12. Bond Energy to Break = Bond Energy Released
Bond Strength
Bond Energy is the energy required to break 1 mole of bonds. (Same energy released when bond forms)
The net bond energy indicates whether the process is exothermic or endothermic.
Bond Energy to Break = Bond Energy Released

13. Practice N2 + H2  N2H4 H4C2 + O2  CO2 + H2O The Process:
Balance the equation
Draw the structures
Add/subtract all bond energies

14. What can cause reaction rates to vary?
Temperature
Concentration
Surface area
Catalysts
What is this?

15. Catalysts A catalyst accelerates the reaction.
Provides different pathway
Lowers activation energy
Reappears as a product
Enzymes are catalysts
Image Credit: wikidot.com

16. Practice
Why are there warnings on some medications not to break, crush, or chew the pill?
Why do some laundry soaps contain enzymes?
What is the chemical purpose of using hot water to clean?
Why are photographic prints processed in the dark?

17. What is an acid? What is a base?
Acids contain H+ and H30+ ions, and are substances that donate hydrogen ions.
Bases contain hydroxide (OH−) ions, or are substances that accept a hydrogen ions.
Proton Donor
Proton Acceptor

18. Practice Identify the acid/base substances. Baking soda (NaHCO3)
HCl + NaHCO3  H2CO3 + NaCl
CH3CO2H + H2O  CH3CO2- + H3O+

19. Strong Acids & Bases
Strong acids and bases completely ionize in water.
Always donate an H+ or an OH−
Some Strong Acids
HNO3
nitric
acid
HCl
hydrochloric acid
H2SO4
sulfuric
Some Strong Bases
LiOH
lithium hydroxide
NaOH
sodium hydroxide
KOH
potassium hydroxide

20. Water & Salts
The neutralization reaction of an acid and a base produces water and a salt.
Acid
Base
Water
Salt
HCl
 + 
NaOH 
H2O
NaCl
HBr
KOH
KBr

21. pH
A substance that has an equal number of acid and base ions is neutral. (pH balanced) pH
Solution
1 to 6
Acidic 7
Neutral
8 to 14
Basic

22. Substance pH Battery Acid 0.5 Stomach Acid 1.5 – 2.0 Cola 2.5
Orange Juice
3.5
Coffee
5.0
Milk
6.5
Human Blood
7.34 – 7.45
Hand Soap
9.0 – 10.0
Ammonia
11.5
Bleach
12.5

23. Practice
If the water you drink has a pH of 6.8, is it acidic, basic, or neutral?
Blood has buffers to help control the natural pH your body needs. The amount of CO2 in the blood stream can change pH. What do we do naturally that can change the pH of blood?

24. water + carbon dioxide carbonic acid (H2CO3)
What is “acid rain”?
Acid Rain is moisture that has a pH of less than 5.
Rain, snow, sleet, or fog
Rainwater normally has a pH of 5.6 to 6.2
Acids may combine with dust (dry deposition)
Water reacts with CO2 in the atmosphere.
water + carbon dioxide carbonic acid (H2CO3)

25. Strong Acids in Our Atmosphere
Human-produced exhaust emissions of sulfur and nitrogen oxides form strong acids.
sulfates + water  sulfuric acid (H2SO4)
nitrates + water  nitric acid (HNO3)

26. Question
Where would you expect a higher level of acidity in the atmosphere, WY or CA? Why? What are the factors?
Image Credit: Wikimedia commons

27.
Images: epa.gov

28. Trees killed by acid rain Czech Republic
Image Credit
Simon Fraser/Science Photo Library

29. What is an oxidation-reduction reaction?
Redox reactions involve a transfer of electrons, and often the addition or subtraction of oxygen.
Oxidation
Reduction
Reactant loses electrons
Reactant gains electrons
Oxygen Added
Oxygen Removed

30. Redox Reactions
Corrosion is a redox reaction between a metal and oxygen (O2).
Combustion is a redox reaction between a non-metal and oxygen (O2).

31. NASA Morpheus Lander Crash and Explosions
Liquid oxygen and methane
Green propellants
Combustion reaction

32. Practice Determined whether elements are oxidized or reduced.
HgS + O2  Hg + SO2
SnO C  Sn + 2CO2
4Fe + 3O2  2Fe2O3

33. CH4(g) + 2O2(g)  CO2(g) + 2H2O(l)
More Practice
Is a combustion reaction, like the combustion of methane, exothermic or endothermic?
CH4(g) + 2O2(g)  CO2(g) + 2H2O(l)
Why would this be a useful reaction to utilize in a space vehicle?

34. How do batteries and fuel cells work?
Batteries have 2 diodes; one that is oxidized and one that is reduced.
Acidic solution reacts with metals
One metal is reduced (+ end)
One metal is oxidized (– end)
Battery

35. Cathode (+) Anode (–) Metal gains e− Metal is reduced Battery
Metal loses e−
Metal is oxidized

36. Fuel Cells A fuel cell uses a membrane to separate the reactants.
Hydrogen gas is oxidized.
Oxygen gas is reduced.
Product is H2O vapor.

37. The Fuel Cell Process Converts hydrogen-rich fuel into electricity
Hydrogen splits into p & e− at anode
p’s pass through electrolyte membrane
e− forced through electric circuit
The protons, electrons, and oxygen combine at the cathode into water
Image Credit: FCHEA.org

38. Practice Where do you store your batteries? Why?
Do you know the difference between a dry cell battery and an alkaline battery? Which lasts longer?
What is the primary difference between a battery and a fuel cell?

39. How Fuel Cells Work Video by: hydrogenandyou
Video by: hydrogenandyou

40. Al2O3 + Energy  Al2 + O2 What is electrolysis?
Electrolysis is the use of electric current to cause chemical change.
Reverses chemical reactions
Splits compounds
Al2O3 + Energy  Al2 + O2

41. Practice Why does the water molecule split apart?
Why are hydrogen and oxygen attracted to different diodes?
Image Credit: Wikipedia

42. More Practice Is electrolysis an exothermic or endothermic process?
Describe the chemical process of recharging your mobile phone device.
Can you think of other examples of electrolysis?