Name ______KEY______Period ______Date ______
“Oh My Goodness” II – The Sequel
Chemistry Second Semester Review
Stoichiometry
1. Define:
a) limiting reagent The reactant that determines the maximum amount of product that can be produced.
b) theoretical yield The amount of product I should be able to produce, based on calculations.
c) actual yield
The amount of product actually made in the lab.
d) percent yield
A comparison of actual yield vs theoretical yield.
2. What does the Limiting Reacting limit? The amount of product produced and the amount of the other reactant(s) consumed.
3. Why does the Limiting Reactant limit the reaction? It runs out first.
Use the following equation to answer questions 4 – 7.
3Na2O + Ca3(PO4)2 → 2Na3PO4 + 3CaO
4. How many moles of sodium oxide will be required to react with 3 moles of calcium phosphate?
3 mol Ca3(PO4)2 / 3 mol Na2O__ = 9 mol Na2O
/ 1 mol Ca3(PO4)2
5. How many grams of Na3PO4 will be produced if 117 grams of Na2O reacts with excess grams of Ca3(PO4)2?
117 Na2O / 1 mol Na2O / 2 mol Na3PO4 / 163.94g___ = 206 g Na3PO4
/ 61.98 g / 3 mol Na2O / 1 mol Na3PO4
6. How many grams of Na2O will be required to react with 4.3 moles of Ca3(PO4)2
4.3 mol Ca3(PO4)2 / 3 mol Na2O / 61.98 g __ = 8.0 X 102 g Na2O
/ 1 mol Ca3(PO4)2 / 1 mol Na2O
7. If excess Na2O is allowed to react with 3 moles of Ca3(PO4)2, how many grams of CaO will be produced?
3 mol Ca3(PO4)2 / 3 mol CaO / 56.08 g__ = 504.72 à 5 X 102 g CaO
/ 1 mol Ca3(PO4)2 / 1 mol CaO
8. Penelope ran a reaction in the lab and produced 97.4 grams of product. According to her calculations, she should have produced only 92.4 grams of product. What was her percent yield?
97.4 X 100 = 105%
92.4
9. Theoretically, 402 grams of product should have been produced in a laboratory experiment. When Stephan did the experiment, he only produced 349 grams. What was his percent yield?
349 X 100 = 86.8%
402
10. Given: N2 + 3H2 → 2NH3
How many grams of NH3 can be produced from the reaction of 28g of N2?
28g N2 / 1mol N2 / 2mol NH3 / 17.04g = 34g NH3
/ 28g N2 / 1mol N2 / 1mol NH3
Thermo Constants and Equations:
Q =(m)(cp)(Δ T)
Cp water = 1 cal/ goC or 4.18 J/ gOC
ΔH = Products - Reactants
11. How many calories are needed to heat 20.0g of Al from 10oC to 50oC?
(Cp of aluminum is 0.215cal/goC).
20.0g x 0.215 x 40oC = 172 cal
12. 1.5 cal are added to 10.0g of a metal, resulting in a 440oC temperature change. What is the specific heat of the metal?
1.5 = 10.0g x Cp x 440oC Cp = 3.4 X 10-4 cal/goC
13. What is the specific heat of silicon (in kJ/g * oC) if the temperature of a 4.11 g sample of silicon is increased by 3.8 oC when 11.1 J of heat is added?
11.1 J / 1 kJ = 0.0111 kJ 0.0111 = 4.11g x Cp x 3.8oC 7.11 X 10-4 kJ/goC
/ 103J
14. When a 25.7 g sample of NaI dissolves in 80.0 g of water in a calorimeter, the temperature rises from 20.5 oC to 24.4 oC. Calculate heat flow into the water as the NaI dissolves.
24.4 – 20.5 = 3.9 80.0g x 1 x 3.9oC = 312 cal
15. A sample of gold is heated, then placed in a calorimeter containing 60.0 g of water. Temperature of water increases from 19.00 oC to 20.00 oC. How much heat was lost by the metal?
60.0g x 1 x 1 = 60.0 cal
16. When a chemical reaction occurs in 75.0 g of water in a calorimeter, the
temperature drops from 31.0 oC to 21.6 oC. Calculate the heat flow. (specific heat of water is 4.18J/g* OC)
75.0g x 4.18 x 9.4oC = 2946.9 à 2.95 X 103 J
17. C2H6(g) à C2H2(g) + 2H2(g) ∆H = +3.2 x 102 kJ/mol
What is an alternate way to write this equation?
A. C2H6(g) à C2H2(g) + 2H2(g) + 3.2 x 102 kJ
B. C2H6(g) + 3.2 x 102 kJ à C2H2(g) + 2H2(g)
C. C2H2(g) + 2H2(g) + 3.2 x 102 kJ à C2H6(g)
D. C2H6(g) – 3.2 x 102 kJ à C2H2(g) + 2H2(g)
18. What characteristic(s) of water change(s) when its temperature is raised from 10ºC to 110ºC at standard pressure?
A. both kinetic and potential energy
B. intramolecular bonding only
C. kinetic energy only
D. potential energy only
19. What happens to the water in a calorimeter when an exothermic reaction occurs in it?
A. It absorbs heat, and a drop in temperature is observed.
B. It absorbs heat, and a rise in temperature is observed.
C. It releases heat, and a drop in temperature is observed.
D. It releases heat, and a rise in temperature is observed.
21. A 10 g sample of water is at 100OC. A 20 g sample of water is at 100OC. Which sample has the highest kinetic energy?______both the same_____ Explain ______Substances at the same temperature have the same average KE______
22. What is heat? ____Energy that is transferred from one body to another.____. In what direction does heat flow? ______from warmer to cooler______
23. Is Heat being absorbed or released as the process goes from I to H?
released
24. What process is occuring as the process moves from K to L?
heating steam
25. What process is occuring as the process moves from K to J?
condensation
26. Is the change that occurs when moving from K to J endothermic or exothermic?
exothermic
27. What type(s) of energy are increasing as the process moves from G to J?
G-H and I-J: kinetic H-I: potential
28. What type(s) of energy changes are decreasing as the process moves from K to J?
potential
29. The temperature does not change as we move from H to I. Does this mean that the heat energy remains the same?
No. It is an increase of potential energy, not kinetic.
30. Equal masses of iron (Cp = .107 cal/goC), Zinc (Cp = .0928 cal/goC), and Nickel (Cp = .1225 cal/goC) are placed into an oven and heated to 200oc. They are then allowed to sit at room temperature to cool.
Which metal will heat up to 200oC the fastest? ______Zn______
Which metal will cool off the fastest?______Zn______
31. Refer to the graph above:
a. Is the reaction endothermic or exothermic?______Endothermic______
b. Would heat be written as a product or a reactant? ______Reactant______
c. What is the approximate value of ∆H (include sign)? ____C – (A+B)______(+)______
d. Which has more enthalpy, the reactants or the products? ____products_____
e. Will the environment become warmer or cooler as the reaction proceeds? ___colder_____
Gases and Gas Behavior
32. Which of the following graphs could represent the relationship between Gas Pressure and Gas Volume with pressure on the Y axis? ______A______
33. Which could represent the relationship between temperature and volume with temperature on the X axis?______B______
34. Which could represent the relationship between temperature and pressure with temperature on the X axis? ______B______
Graph A Graph B
35. A decrease in temperature means that the particles are moving _slower_ (slower/ faster).
36. What Celsius temperature is referred to as absolute zero? ___-273 oC / 0 K____
37. Convert the following: 304K = __31__ C 22C = _295__ K
38. Anything which decreases the number of collisions between gas particles and container walls will decrease ____pressure_____.
39. In a perfect vacuum, the pressure is 0. What does that say about the number of particles that would be in a perfect vacuum. Zero particles
40. If pressure remains constant, gas volume will decrease when gas temperature _____decrease_____ (increases/decreases).
41. If volume is held constant, pressure will decrease when temperature _____decrease_____ (increases/decreases).
42. If the temperature of a gas in a balloon increases
a. How does the kinetic energy change?______increases______
b. How does the volume of the balloon change?______increases______
c. How does the pressure in the balloon change?______increases______
43. What are the temperature and pressure conditions of STP? ____0_____OC
and _____1____ atm.
44. If a gas at STP has a volume of 22.4L, how many moles of gas are in the container? ___1 mole___
45. According to Kinetic Molecular Theory, is the volume of the individual gas particles important? ______No______
46. According to Kinetic Molecular Theory,
a. Do gas particles collide with each other? ______Yes______
b. Do the gas particles attract each other? ______No______
c. Do the gas particles repel each other? ______No______
47. If the Pressure of a gas at 1 atm is changed to 3 atm at a constant temperature, how will the volume of the gas change? ______decrease to 1/3 of original______
48. If the Kelvin Temperature of a gas in a rigid container is doubled, how will the pressure of the gas change? ______pressure will double______
49. If the pressure exerted on 240.0mL of hydrogen gas at a constant temperature is increased from 325mmHg to 550mmHg, what will be the final volume of the sample?
P1V1 = P2V2 325 x 240 = 550 x V2 V2 = 141.8 mL
50. To what temperature must a sample of nitrogen at 27°C and 0.625 atm be heated so that its pressure becomes 1.125 atm at constant volume?
P1 = P2 0.625 atm = 1.125 atm T2 = 540K 540-273 = 267oC
T1 T2 300K T2
51. Three gases occupy the same container. Gas A exerts a pressure of 1 atm. Gas B exerts a pressure of 2 atm. Gas C exerts a pressure of 3 atm. What is the total pressure in the container? ______1 + 2 + 3 = 6 atm______
52. A mixture of gases contains 20% oxygen, 35% nitrogen, and 45% hydrogen by volume. The total pressure in the container is 885 torr. What is the partial pressure of
a. the oxygen? ___177 torr___
b. the nitrogen? ___310 torr__
c. the hydrogen?___398 torr__
53. What is Avogadro’s Law? ___If the amount of gas in a container increases, the volume increases (if P and T are constant).___
54. If some gas is removed from a container but the pressure and temperature remain the same, how will the volume of the container change? ______decrease______
Solution Equations:
Molarity = moles / L Dilutions formula: M1V1 = M2V2
55. A solution is a _____homogeneous______mixture.
56. List three factors that affect how quickly a solute dissolves.
______Temp______, _____agitation_____, and ______particle size______
57. Define the following:
a. Solute The dissolved particles. The substance in lesser amount.
b. Solvent The dissolving medium. The substance present in greater amount.
c. Miscible Liquids dissolve in each other. (Alcohol and water)
d. Immiscible Liquids are insoluble in each other. (Oil and water)
e. Polar molecule One end is slightly positive and one end is slightly negative.
f. Electrolyte A solution that conducts electricity. (Ionic compounds dissolved in water.)
g. Solubility The amount of a solute that will dissolve in an amount solvent at a given temp.
h. Concentration Measure of the amount of a solute dissolved in a given quantity of solvent.
i. Dilute solution Small amount of solute. (Low concentration)
j. Concentrated solution Large amount of solute. (High concentration)
k. Molarity
Number of moles of solute dissolved in 1 liter of solution (M).
l. Stock solution The concentrated solution.
58. Water has a much higher boiling point than other molecules of similar size. What is the property of water that causes it to have such a high boiling point? ______polarity______
59. What types of compounds will dissolve in water? __ionic and polar molecular__
60. What type of compound will not dissolve in water? ___non-polar molecules____
61. Consider the graph below
a. What is the solubility of KNO3 at 80°C? ______170g / 100g______
b. How many grams of KCl will dissolve in 65g of water at 80°C? _32.5g KCl___
c. Does the solubility of KCl increase or decrease as the temperature increases?
increases
d. 90 g of KNO3 are dissolved in water at 60OC. The solution is then cooled to 40OC. No precipitate is observed. Is this solution now saturated, unsaturated, or supersaturated? _____supersaturated_____
62. At 40°C, the solubility of KNO3 in water is 60g/100g (see graph from question 61). Identify the following solutions as:
A. unsaturated B. saturated C. supersaturated
a. 25g of KNO3 is placed in 50g of water at 40°C. All of the solute dissolves. ___A___
b. 24g of KNO3 is stirred into 40g of water at 40°C. All of the solute dissolves. __B__
c. 35g of KNO3 is stirred into 50g of water at 40°C. NOT all of the solute dissolves. ___B___
d. 35g of KNO3 is stirred into 50g of water at 40°C. NOT all of the solute dissolves. The container is then heated to 90°C. All of the solute dissolves and remains in solution when the temperature is returned to 40°C. ___C___
63. A student is given a solution and asked to determine if the solution is saturated, unsaturated, or supersaturated. The student drops one solute crystal into the solution. How should the student interpret the possible outcomes of his experiment?
a. Outcome 1. The crystal dissolves ______unsaturated______
b. Outcome 2. Many crystals rapidly appear in the solution. ___supersat._____
c. Outcome 3. The crystal falls to the bottom of the container.___saturated___
64. According to the graphed relationships shown above:
a. Do gases become more soluble at higher temperatures or lower temperatures?
Lower temp
b. Do solids become more soluble at higher temperatures or lower temperatures?
Higher temp
c. How is the solubility of a gas in a liquid affected by a decrease in temperature?
Increase in solubility