Chem Sem 2 Exam Review Answers
1. When balancing a chemical equation,
a. you must insert subscripts or coefficients? coefficients
b. And why? Due to the conservation of mass, the number of atoms we started
with must equal the same number of atoms we finish with.
2. Balance the following equation:
2Li + 2H2O  2LiOH + H2
3. What is the formula for Calcium fluoride? CaF2
4. Balance the following equation and then tell me the mole ratio:
2H2O + 4KO2  4KOH + 3O2
Mole ratio: 2:4:4:3
5. 10 moles of Gallium has a mass of? (5.08)
69.72 𝑔 𝐺𝑎
10 mol Ga X 1 𝑚𝑜𝑙𝑒 𝐺𝑎 = 697.2 g Ga (700 g Ga if considering significant figures)
Use the following reaction to answer the questions below:
H2O  H2 + O2
6. Balance the reaction.
2H2O  2H2 + O2
7. What is the mole ratio of H2O to O2? 2:1
8. When 15 grams of H2O decomposes how many grams of O2 are formed?
1 𝑚𝑜𝑙𝑒 𝐻2𝑂
1 𝑚𝑜𝑙𝑒 𝑂2
32 𝑔 𝑂2
15 g H2O X
X
X
= 13.33 g O2 (13 g O2 with
18.01 𝑔 𝐻2𝑂
2 𝑚𝑜𝑙𝑒𝑠 𝐻2𝑂
1 𝑚𝑜𝑙𝑒 𝑂2
significant figures)
Use the following reaction to answer questions 9-11 below:
LiH + AlCl3  LiCl + LiAlH4
9. Balance the reaction
4LiH + AlCl3  3LiCl + LiAlH4
10. How many moles of LiH are required to make 1 mole of LiAlH4?
1 mole LiAlH4 X
4 𝑚𝑜𝑙 𝐿𝑖𝐻
1 𝑚𝑜𝑙𝑒 LiAlH4
= 4 moles LiH
11. 6 moles of LiH will produce how many moles of LiAlH4?
6 mole LiH X
1 𝑚𝑜𝑙 𝐿𝑖𝐴𝑙𝐻4
4 𝑚𝑜𝑙𝑒 𝐿𝑖𝐻
= 1.5 mol LiAlH4
12. List the three states of matter from the most to least energetic.
Gas>liquid>solid
13. What affect does altitude have on boiling point?
As altitude increases, the atmospheric pressure decreases. Boiling point of a liquid is
the temperature at which the vapor pressure equals the atmospheric pressure. Since
there is a reduced atmospheric pressure, we will need a reduced vapor pressure for
boiling to occur. This reduces the amount of energy required to boil water, thus lowering
the boiling point of a liquid.
14. What affect does altitude have on atmospheric air volume? See answer #13
15. A diver goes down to a depth of 132 feet. How many atmospheres of pressure are
on the diver?
1 𝑎𝑡𝑚
132 feet X
= approx 4 atm from the water and 1 from the
34 𝑓𝑒𝑒𝑡 𝑤𝑎𝑡𝑒𝑟
air.
The final answr is 5 atm.
16. Convert 2.5 atmospheres to mmHg
2.5 atm X
760 𝑚𝑚𝐻𝑔
1 𝑎𝑡𝑚
= 1900 mmHg
17. A basketball with a volume of 4.75 Liters is left in a car when the temperature is 298
K. What will the volume of the ball be as the car heats up to 309 K during the day?
V1 = 4.75 L
T1 = 298 K
V2 = ?
T2 = 309K
𝑉1
𝑇1
=
4.75 𝐿
298 𝐾
V2 =
𝑉2
𝑇2
=
𝑉2
309 𝐾
(4.75 𝐿) (309𝐾)
298 𝐾
V2 = 4.93 L
18. Define Temperature and Heat.
Heat is the measurement of the average kinetic energy of the particles in a substance,
whereas temperature is the measurement of the amount of heat of a substance
19. Which conversion factor below would be used to change liters gas to moles of gas?
We would use Molar Volume: 1 mol = 22.4 L
20. Define Chemical Equilibrium and Reversible Reaction
Chemical equilibrium is a reaction in which the forward reaction occurs at the same rate
as the reverse reaction. At equilibrium, the concentration of reactants and products
remain constant.
A reversible reaction is one where the reactants form products and the products simply
break down to reform the reactants at the same time (eventually reaching equilibrium
where the reactions occur at the same rate).
21.
Graph B. Equilibrium is the state in which the concentration of reactants and products
remain constant.
22. How does temperature affect the rate of a reaction on the molecular level? As
temperature increases, the molecules will increase in speed. This will cause more
collisions, thus causing the reaction to occur faster.
23.
The activation energy is ‘b’.
24.
The energy of the reactants is higher. Since this reaction ‘lost’ energy, it is exothermic.
25. Define endothermic and exothermic.
An endothermic reaction is when heat is absorbed and the temperature of the vessel
decreases. The enthalpy (the heat absorbed or releases by a process running at a
constant pressure) change is positive and the bond is breaking.
An exothermic reaction is when heat is released and the temperature of the vessel rises.
The enthalpy (the heat absorbed or releases by a process running at a constant
pressure) change is negative and the bond is formation.
26.
The reaction is exothermic.
27. Define the Haber Process and be able to identify it.
The Haber process is where hydrogen gas and nitrogen gas react to form ammonia.
The reaction is: N2 + 3H2  2NH3
28. Define pH.
The pH is the measure of the concentration of H+ ions in solution.
29. High H+ concentrations indicates a
a. basic solution
b. acidic solution
30. A substance used to determine whether a solution is acidic, basic or neutral is a …
acid/base indicator (like the cabbage juice you used in one of the labs)
31. Chemical properties of hydrogen compounds can have vast differences depending
on the state of matter that the substance is in - solid, liquid or gas. The difference in
chemical properties is related to…the molecular structure and/or the dissociation of H+
from the hydrogen compound into solution.
32. What happens in a reduction reaction? A substance gains electrons
33. What happens in a oxidation reaction? A substance loses electrons
34. Identify the reaction as oxidation or reduction:
Cu+4 + 2e- →Cu+2
This is a reduction reaction as Cu+4 ion gained two electrons to form the Cu+2 ion.
35. What is the oxidizing agent and reducing agent in the following equations:
Oxidizing Agent - that substance which oxidizes somebody else. It is reduced in the process.
Reducing Agent - that substance which reduces somebody else. It is oxidized in the process.
Reaction
4NaF + O22Na2O + 2F2
Mg + Cl2  MgCl2
2H2 + O2  2H2O
Oxidizing Agent
Na
Cl2
O2
Reducing Agent
F
Mg
H2
36. Convert 3 atm to torr.
760 𝑡𝑜𝑟𝑟
3 atm X 1 𝑎𝑡𝑚 = 2280 torr
37. A gas with a volume of 2.75 L is known to contain 0.766 mol. Keeping the
temperature and pressure constant, if the amount of gas is increased to 2.89 mol, what
will be the new volume?
V1 = 2.75 L
N1= 0.766 mol
N2 = 2.89 mol
V2 = ?
𝑣1
𝑛1
𝑣2
= 𝑛2
2.75 𝐿
0.766 𝑚𝑜𝑙
V2 =
𝑣2
= 2.89 𝑚𝑜𝑙
(2.75 𝐿)(2.89 𝑚𝑜𝑙)
0.766 𝑚𝑜𝑙
V2 = 10.4 mol
38. What are the three basic types of compounds that are used as antacids?
Calcium carbonate , magnesium carbonate, and sodium bicarbonate
39. Acids react with metals to produce hydrogen.
36. Neutralization reaction of an acid with a base always produces salt and water.
37. The concentration of hydronium ions in a solution is 1 x 10-9, What is the pH of the
solution?
pH = -log[H+]
pH = -log(1 x 10-9)
pH = 9
38. What is the oxidation number of Pb in PbSO4?
PbSO4
Oxidation #’s: (?)(-2)(-2*4)
Pb oxidation number has to be +10
39. Calculate the number of atoms in 20.5 g Carbon
1 𝑚𝑜𝑙 𝐶
20.5 g C X 12.01 𝑔 𝐶 X
6.02 𝑋 1023 𝑎𝑡𝑜𝑚𝑠
1 𝑚𝑜𝑙𝑒 𝐶
= 1.03 X 1024 Carbon atoms
40. Determine the molar mass of Sodium Carbonate.
Na2CO3
Na = 2 X 22.99 = 45.98
C = 1 X 12.01 = 12.01
O = 3 X 16
= 48
45.98 + 12.01 + 48 = 105.99 g/mol
Use the following reaction to answer the questions below:
Li + N2 Li3N
41. Balance the reaction
6Li + N2 2Li3N
42. How many moles of Li3N will be produced if you begin with 8.5 moles of Li ?
2 𝑚𝑜𝑙 𝐿𝑖3𝑁
8.5 mol Li X
= 2.83 mol Li3N
6 𝑚𝑜𝑙 𝐿𝑖
43. Determine the mass of sodium chloride produced when 2.5 moles of chlorine gas
reacts with sodium. 2Na + Cl2  2NaCl (be sure to balance the reaction first!)
2.5 mol Cl2 X
2 𝑚𝑜𝑙 𝑁𝑎𝐶𝑙
1 𝑚𝑜𝑙 𝐶𝑙2
X
58.44 𝑔 𝑁𝑎𝐶𝑙
1 𝑚𝑜𝑙 𝑁𝑎𝐶𝑙
= 292.2 g NaCl
46. Match the reaction type with the reaction:
Synthesis
Single Replacemet
Double Replacement
Combustion
Decomposition
2Na + Cl2  2NaCl
Synthesis
4NaF + O22Na2O + 2F2
Single replacement
4LiH + AlCl3  3LiCl + LiAlH4
Double replacement
2H2O 2H2 + O2
Decomposition
47. Bases turn blue litmus red. True or False? False
48. What is oxygen’s oxidation number? -2