Equilibrium & LeChatlier’s Principle
1. Saturated solutions are examples of substances in a state of physical equilibrium. What two things are equal to
each other in saturated solutions? remember: at equilibrium CARE (Constant Amounts, Rates are Equal). In a
saturated solution, the rate of dissolving = the rate of recrystallizing
2. At chemical equilibrium, what is equal? The RATES (SPEEDS) of the forward and reverse reactions
3. What does LeChatlier’s Principle say?
A system at equilibrium will shift to lessen the effects of a stress applied to the system (i.e. a change in
temperature, concentration, or pressure)
 A system will shift AWAY from an INCREASE (concentration, temperature) UP & AWAY
 A system will shift TOWARD a DECREASE (concentration, temperature) Touch Down
 If pressure is increased on a system of all GASES, equilibrium will shift AWAY from the side with the
MOST gas particles (fewer particles fit better in a smaller volume)
 If pressure is decreased on a system of all GASES, equilibrium will shift TOWARD the side with the
MOST gas particles (more particles fit better in a bigger volume)
4. What happens to the concentration of a gas if the pressure is increased? increases
5. What happens to the concentration of a gas if the pressure is decreased? decreases
6. Given the following reaction at equilibrium:
2 CO(g) + O2(g)
2CO2(g) + heat
a. Which reaction will be favored if…
i. CO is removed from the system? reverse
ii. carbon dioxide is added to the system?
reverse
iii. the pressure is decreased? reverse
b. What will happen to the system if…
i. a catalyst is added? Nothing (both the
forward and reverse reactions will speed up
equally)
ii. the temperature is increased? Shift to the
left; more CO and O2 will form; CO2 will be
used up
iii. more oxygen is added?
Shift to the right; more CO2 will form; CO and
O2 will be used up
7. Given the following reaction at equilibrium:
H+(aq) + OH–(aq)
H2O (l)
∆H = -55.8 kJ
a. What will happen to the system if…
i. H2O is removed from the system? Shift
to the right;
ii. heat is added to the system? Shift to
the left
iii. the pressure is decreased? Nothing –
no gases in this system
b. If a base is added to the system,
i. What will happen to the amount of H+?
H+ will decrease because there will be
more OH- from the base to react with
ii. What will happen to the amount of
water? H2O will increase because more
OH- from the base will react with H+ to
form water
8. Nitrogen gas, hydrogen gas, and ammonia gas are in equilibrium in a closed container at constant temperature
and pressure. The equation below represents this equilibrium.
N2(g) + 3H2(g)
2NH3(g)
The graph below shows the initial concentration of each gas, the changes that occur as a result of adding H2(g)
to the system, and the final concentrations when equilibrium is re-established.
a. What information on the graph indicates that the system was initially at equilibrium? Constant
concentrations/amounts
b. Explain, in terms of LeChatelier’s principle, why the final concentration of NH3(g) is greater than the initial
concentration of NH3(g). More H2 was added to the system. According to LeChatlier’s principle, a system at
equilibrium will move away from an increase in concentration. The reaction shifted to the right, which
produced more NH3.
c. Explain, in terms of collision theory, why the concentration of H2(g) begins to decrease immediately after more
H2(g) is added to the system. As more H2 was added, more collisions occurred between reactant particles,
which caused them to react and form more NH3.
Acids, Bases, and Salts
1. What is something acids, bases, and salts have in common? They are all ELECTROLYTES (conduct electricity in
SOLUTION).
2. Which ion do Arrhenius acids release in solution? H+ or H3O+
3. Which ion do Arrhenius bases release in solution? OH4. What is the alternate definition of an acid? proton donors/H+ donors
5. What is the alternate definition of a base? proton acceptors/H+ acceptors (BAH+!)
6. What is the chemical formula for ammonia? Is it an acid or a base? NH3 (base)
7. Write and balance the chemical equation for the neutralization reaction between carbonic acid and magnesium
hydroxide. Name the salt that is produced in this reaction.
H2CO3 + Mg(OH)2  2H2O + MgCO3
salt: magnesium carbonate
H
4
H
2 4
C
1
C
1
O
5
O
4 5
Mg
1
Mg
1
8. Write and balance the chemical equation for the neutralization reaction between perchloric acid and sodium
hydroxide. Name the salt that is produced in this reaction.
HClO4 + NaOH  H2O + NaClO4
H
Cl
O
Na
2
1
5
1
H
Cl
O
Na
salt: sodium perchlorate
2
1
5
1
9. What is molarity? What is the symbol for molarity? moles solute/liter solution; symbol is M
10. What is the molarity of 3 liters of a solution containing 2 moles of NaOH?
MB = moles OH-/liter solution
MB = 2 moles OH-/3L = 0.67M
11. What is the molarity of 3 liters of a solution containing 2 moles of Ca(OH)2?
MB = moles OH-/liter solution
MB = 4 moles OH-/3L = 1.3M
12. What is the volume of a 2M solution of HBr that is required to neutralize 10 milliliters of a 5M NaOH solution?
MAVA = MBVB
2M x VA = 5M x 10mL
VA = 25 mL
13. What is the molarity of a solution of hydroiodic acid if 85mL of 10M calcium hydroxide are needed to neutralize
50mL of the acid?
MAVA = MBVB
MA x 50mL = 10M x 85mL
MA = 17M
14. For the following, state whether a chemical reaction will occur. If so, write and balance the chemical equation.
(TABLE J)
a. Sn and HCl yes
Sn + 2HCl  SnCl2 + H2
b. Au and HCl no
c. Ca and H2SO4 yes
Ca + H2SO4  CaSO4 + H2
d. Pb and HNO3 yes
Pb + 2HNO3  Pb(NO3)2 + H2
15. A strong acid spill changes the pH levels of the soil in a field 1000-fold. If the original pH of the soil in the field
was 7, what is the new pH of the soil?
1000 = 103 (the pH level changes by 3 units – it is lowered by 3 since it is becoming more acidic)
new pH = 4
16. A lake affected by acid rain has a pH of 4.5. A base is added to the lake to neutralize some of the acid. Enough
base is added to change the pH of the lake a hundred-fold. What is the new pH of the lake?
100 = 102 (the pH level changes by 2 units – it is raised by 2 since it is becoming more basic)
new pH = 6.5
17. Compare the concentrations of H+ and OH- in a neutral solution. they are equal
18. Compare the concentrations of H+ and OH- in an acidic solution. H+ is greater than OH19. Compare the concentrations of H+ and OH- in a basic solution. OH- is greater than H+
20. What three indicators could be used to differentiate between solutions of pH 3 and 6? Methyl orange, litmus,
bromcresol green
Redox
1.
2.
3.
4.
5.
What is the oxidation state of phosphorus in Na3PO4? +5
What is the oxidation state of sodium in a sample of Na(s)? 0
What is the oxidation state of O in O2? 0
Is an element oxidized or reduced when it loses electrons? (LEO) oxidized
Is an element oxidized or reduced when it gains electrons? (GER) reduced
0
0
+1 -1
6. Given the following reaction: H2 + F2 → 2 HF
a. Which species is oxidized? H2
b. Which species is reduced? F2
c. In the reaction above, electrons are transferred from H2 to F2
+1
d. Write the balanced half-reaction for the oxidation reaction. H2  2e- + 2H
-1
e. Write the balanced half-reaction for the reduction reaction. F2 + 2e-  2F
f.
If 4 moles of electrons are gained by fluorine, how many moles of electrons must be lost by hydrogen? 4
Electrochemistry
1. What are the three types of compounds (electrolytes) that will conduct electricity in the liquid, molten, or
aqueous phases? Acids, bases, and salts
2. What type of element will conduct electricity in the molten phase and as solids? METALS
3. At which electrode does oxidation always occur? (AnOx) ANODE
4. At which electrode does reduction always occur? (RedCat) CATHODE
5. In which direction do electrons flow (from which electrode to which electrode)? From anode to cathode
6. Which electrode always gains mass? Cathode (because positive ions (in solution) are being reduced to form
neutral atoms which, being uncharged, do not like to stay in solution and are deposited on the metal strip that
forms the cathode)
7. Which electrode always loses mass? Anode (because neutral atoms that make up the metal strip that forms
the anode are being oxidized (losing electrons) and forming positive ions that will go into solution – the anode
is essentially “dissolving” away)
8. What is another name for a voltaic cell? A battery
9. What is the purpose of the salt bridge in a voltaic cell? To permit the migration (movement) of IONS
10. In a voltaic cell, chemical energy is converted into what type of energy? electrical
11. A voltaic cell involved a (spontaneous, nonspontaneous) redox reaction that (releases, requires) energy.
12. In a voltaic cell, the metal listed higher on Table J is the one that (loses, gains) electrons and is (oxidized,
reduced).
13. In an electrochemical cell, the metal listed higher on Table J is the one that (loses, gains) electrons and is
(oxidized, reduced).
14. What is electrolysis? Is it spontaneous or nonspontaneous? Does it release or require energy?
Electrolysis is a type of redox reaction in which a compound is broken apart into its elements.
Ex: 2H2O  2H2 + O2
15. What is electroplating? Is it spontaneous or nonspontaneous? Does it release or require energy?
Electroplating is a type of redox reaction in which some material is coated or plated with a metal
Ex: gold-plated jewelry
Organic Chemistry
1. Refer to notes/blue packet/quiz to review naming of organic compounds.
2. Identify the following type of organic reaction occurring for each of the following:
a. nC2H2 → (C2H2)n POLYMERIZATION
b. C4H10 + Cl2 → C4H9Cl + HCl SUBSTITUTION
c. C6H12O6 → 2C2H5OH + 2CO2 FERMENTATION
d. C5H10 + H2 → C5H12 ADDITION
e. C2H4 + I2 → C2H4I2 ADDITION
f. C2H4 + 3 O2  2 H2O + 2 CO2 COMPLETE COMBUSTION
g. CH3COOH + CH3OH  CH3COOCH3 + H2O ESTERIFICATION
3. Write the word equation for a saponification reaction. Ester + base  soap + alcohol
4. What are the products of complete combustion? CO2 and H2O
5. What are the products of incomplete combustion? CO and H2O
6. What are three natural polymers? Starches, proteins, cellulose
7. What are three synthetic polymers? Nylon, rubber, plastics (polyethylene)
Miscellaneous
1. Which measurement contains a total of three significant figures? (0.010g, 0.01g, 0.0100g, 0.01000g)
2. Balance the following chemical reactions and identify the type(s) of reaction they are.
a. N2 + O2 → N2O5
2N2 + 5O2 → 2N2O5
Synthesis, redox
b. Al + CuSO4 → Al2(SO4)3 + Cu
2Al + 3CuSO4 → Al2(SO4)3 + 3Cu
Single replacement, redox
c. NaOH + H3PO4 → Na3PO4 + H2O
3NaOH + H3PO4 → Na3PO4 + 3H2O
Neutralization, double replacement
d. ZnBr2(aq) + AgNO3(aq) → Zn(NO3)2(aq) + AgBr(s)
ZnBr2(aq) + 2AgNO3(aq) → Zn(NO3)2(aq) + 2AgBr(s)
Double replacement
e. Al(s) + CuCl2(aq) → AlCl3(aq) + Cu(s)
2Al(s) + 3CuCl2(aq) → 2AlCl3(aq) + 3Cu(s)
Single replacement, redox
f.
2Ag2O(s) → 4Ag(s) + O2(g)
2Ag2O(s) → 4Ag(s) + O2(g)
Decomposition, redox (electrolysis)