Download Unit 13 Worksheet Answers

Name_______________________________________period_______unit 13 worksheet kinetics and equilibrium
1) What is meant by the term "rate of reaction"?
How fast a reaction occurs
2) It is found that a 10oC increase in temperature roughly doubles the rate of many chemical reactions. If a reaction
takes 20 seconds at 40oC, how long would it take at 60oC? 5 seconds
3) Use the collision theory to explain why each factor (concentration, temperature, surface area) alters the rate of a
reaction.
They each cause more collisions so the reaction can happen faster. The temperature also causes the collisions to
happen with more energy so there are more effective collisions.
4) It has been found that rates are more rapid at the beginning of a reaction than toward the end, assuming the
temperature is constant. Explain why. As a reaction proceeds, the concentration of reactants decrease so the
reaction slows down
5) Enzymes act as catalyst in our bodies and help our muscles move. Why do you think your hands seem to “stiff” when they are
cold? Reactions are slower at colder temperatures
6)
Due to the decomposition reactions with oxygen or carbon dioxide in the air, meat begins to feel slimy and smell spoiled. Explain, using your
knowledge of chemical kinetics, why meat spoils less rapidly when left unsliced?
Reactions are slower when there is less surface area
7) For each energy diagram below, label reactants, products, ∆H, E a , and tell if it is endothermic or exothermic.
Endothermic
exothermic
8) How would each of the energy diagrams in the previous problem change if a catalyst were added to the reaction.
(show using dashed lines) lower activation energy
9) Explain why there is a danger of explosion in places such as coal mines, saw mills, and grain elevators, where large
amounts of dry, powdered combustible materials are present.
High surface area so the reaction happens faster (easier to combust)
10) For each of the following pairs, choose the substance or process you would expect to react more rapidly.
a) Granulated sugar or powdered sugar powdered sugar
b) Zinc in HCl at 298 K or zinc in HCl at 410 K 410 K
c) 5 g of thick platinum wire or 5 g of thin platinum wire 5 g of thin wire
11) What is meant by the normal boiling point of a substance? Boiling point at sea level
12) Explain why the vapor pressure of a liquid increases with increasing temperature.
More evaporation so there is more pressure
13) Which of the following would have a higher vapor pressure at 30 °C, H 2 S (polar) or H 2 O (polar)?
H2S
14) Water boils at 71 C on top of Mt. Everest (8848 m above sea level) and at 86 C on top of Mt Whitney (4418
m above sea level). Why does water boil at a higher temperature on Mt. Whitney than on Mt. Everest?
Boiling occurs when vapor pressure = outside pressure, since Mt. Whitney is lower, there is more
outside pressure so the water will boil at a higher temperature
15) For the reaction below, which change would cause the equilibrium to shift to the right?
CH4(g) + 2H2S(g) + heat ↔ CS2(g) + 4H2(g)
(a) Decrease the concentration of dihydrogen sulfide.
(b) Increase the temperature of the system.
(c) Increase the concentration of carbon disulfide.
(d) Decrease the concentration of methane (CH 4 ).
16) In what direction will the equilibrium shift when the following changes are made to the equilibrium system
below?
2SO3(g) + heat ↔ 2SO2(g) + O2(g)
(a) Sulfur dioxide is added to the system. left
(c) Sulfur trioxide is removed from the system. left
(b) Oxygen is removed from the system. right
(d) Decrease the temperature of the system. left
17) What would happen to the concentration of oxygen when the following changes are made to the reaction
below?
2HgO(g) ↔ Hg(g) + O2(g) + heat
(a) HgO is added to the system increase
(c) decrease the temperature of the system. increase
(b) Hg is added to the system. decrease
(d) the volume is decreased. No change
18) Predict the effect of decreasing the temperature on the position of the following equilibrium.
(a) H 2 (g) + Cl 2 (g) ↔ 2HCl(g) + 49.7 kJ right
(c) 2NH 3 (g) ↔ N 2 (g) + 3H 2 (g) Δ H = 37.2 kJ left
(b) CO(g) + H 2 O(g) ↔ CO 2 (g) + H 2 (g) Δ H = -27.6 kJ right
19) Consider the following equilibrium: 2NO 2 ↔ N 2 O 4 + heat
a. In what direction will the equilibrium shift when NO 2 is removed? left
b. What happens to the amount of N 2 O 4 when the temperature is increased? decrease
c. What happens to the amount of NO 2 when N 2 O 4 is added? Increase
d. In what direction will the equilibrium shift when the volume of the container is decreased? right
e. Is this reaction endothermic or exothermic? Will it getter hotter or colder? Exothermic, hotter
20) For the following reaction, ∆H = 2816 kJ: 6CO 2 (g) + 6H 2 O(l) ↔ C 6 H 12 O 6 (S) + 6O 2 (g)
How is the equilibrium yield of C 6 H 12 O 6 affected by
a. Increasing the pressure of carbon dioxide increases
d. Increasing the temperature increases
b. Decreasing the total pressure no change
e. Removing carbon dioxide decreases
c. Adding a catalyst no change
21) Which describes a system that has reached chemical equilibrium?
a. No new product is formed by the forward reaction.
b. The reverse reaction no longer occurs in the system.
c. The concentration of reactants in the system is equal to the concentration of products.
d. The rate at which the forward reaction occurs equals the rate of the reverse reaction.
Review:
22) When do electrons release photons(packets of energy)? When the electrons:
a. move to higher levels of energy
c increase orbital speed around the nucleus
b. return to their original energy level
d. are released by the atom
23) Helium was discovered on the sun in 1868, almost 30 years before it was discovered here on the earth. How could that be
possible?
a. Investigation of light from the sun revealed a spectrum not yet found in known elements.
b. Captured cosmic rays from the sun contained helium.
c. Investigation of the size of solar flares suggested that they consisted of material twice the mass of hydrogen.
d. Meteorites that had traveled through the sun’s atmosphere contained helium.
24) What is the molar mass of Ca (PO ) ? 310 g/mol
3
4 2
25) Atoms of metals tend to
a. lose electrons and form negative ions
c. gain electrons and form negative ions
b. lose electrons and form positive ions
d. gain electrons and form positive ions
26) Which of these elements has physical and chemical properties most similar to silicon (Si)?
b. silver (Ag)
c. phosphorus (P)
a. germanium (Ge)
27) How many neutrons are in Antimony -122? 71
d. chlorine (Cl)
28) All the isotopes of a given atom have:
a. the same atomic mass and the same atomic number
c. different atomic mass but the same atomic number
b. the same atomic mass but different atomic numbers
d. different atomic mass and different atomic numbers
29) Which pair of atoms will share electrons when a bond is formed between them?
c. K and Cl
a. Ba and I
b. Br and Cl
d. Li and I
30) The proper relationship of wavelength to light energy (E) is:
a. increased wavelength correlates to increased energy
c. wavelength is independent of energy
b. increased wavelength correlates to decreased energy
d. wavelength is independent of frequency
31) When an atom loses an electron, the atom becomes an ion that is
a. positively charged and gains a small amount of mass
c. negatively charged and gains a small amount of mass
b. positively charged and loses a small amount of mass
d. negatively charged and loses a small amount of mass
32) Which solution is more effective at raising the boiling point of water, 0.5 m NaCl, 0.5 m CH 3 OH, or 0.5 m
AlCl 3 ?
33) If 6.5 moles of hydrogen reacts with silver phosphate, how many grams of silver will be produced?
1400g
34) Which of the following will conduct electricity? (there can be more than one answer)
a. solid Mg
b. solid NaCl c. aqueous MgCl 2
d. liquid Sn
e. solid CO 2
35) Write the net ionic equation for each of the following
a. nitrous acid is added to potassium hydroxide
HNO 2 + OH-  H 2 O + NO 2 b. lithium sulfate is added to barium nitrate and a precipitate forms
SO 4 2- + Ba2+  BaSO 4
f. liquid N 2