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1 | |
What role does air play in combustion? |
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2 | |
For a given amount of energy to be used for its propulsion, a spacecraft must have much larger tanks than an airplane. Why? |
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3 | |
Which of the following are exothermic reactions and which are endothermic?
a. The explosion of dynamite
b. The burning of methane
c. The decomposition of water into its elements
d. The dissociation of water into ions
e. The burning of iron in chlorine
f. The combination of zinc and sulfur to form zinc sulfide |
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4 | |
From the observation that the slaking of lime [addition of water to CaO to form Ca(OH)2] gives out heat, would you conclude that the following reaction is endothermic or exothermic?
Ca(OH)2 → CaO + H2O |
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5 | |
In what fundamental way is the explosion of an atomic bomb different from the explosion of dynamite? |
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6 | |
What is the origin of the energy liberated in an exothermic reaction? |
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7 | |
What is the chief reason that reaction rates increase with temperature? |
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8 | |
Why does an increase in temperature increase the rate of exothermic as well as endothermic reactions? |
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9 | |
When carbon in the form of diamond is burned to produce CO2, more heat is given off than when carbon in the form of graphite is burned. What form of carbon is more stable under ordinary conditions? What bearing does this conclusion have on the origin of diamonds? |
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10 | |
Suggest three ways to increase the rate at which zinc dissolves in sulfuric acid. |
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11 | |
Give two examples of reactions that are (a)practically instantaneous at room temperatures, (b) fairly slow at room temperatures. |
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12 | |
Under ordinary circumstances coal burns slowly, but the fine coal dust in mines sometimes burns so rapidly as to cause an explosion. Explain the difference in rates. Would you expect the danger from spontaneous combustion to be greater in a coal pile containing principally large chunks or in one containing finely pulverized coal? Why? |
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13 | |
Why is a reaction with a high activation energy slow at room temperature? |
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14 | |
The solubility of a gas in a liquid decreases with increasing temperature. From this observation and what you know of how a change in temperature can affect an equilibrium, would you expect that dissolving a gas in a liquid is an exothermic or an endothermic process? |
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15 | |
To what extent does the time needed for a strong acid to neutralize a strong base in solution depend on temperature? |
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16 | |
How common are reversible chemical reactions? |
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17 | |
Can you think of the general condition for a reaction to go to completion instead of an equilibrium being established? Give examples of liquid-phase reactions that go to completion. |
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18 | |
Methanol (CH3OH) can be synthesized from carbon monoxide and hydrogen by the reversible reaction
CO + H2 ⇔ CH3OH + energy
If the temperature in the reaction chamber is increased, what happens to the yield of methanol? If the pressure is increased, what happens to the yield of methanol? Why? |
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19 | |
Hydrogen sulfide gas dissolves in water and ionizes very slightly:
H2S ⇔ 2H+ + S2-
How would the acidity of the solution (concentration of H+) be affected by
a. increasing the pressure of H,2S?
b. raising the temperature?
c. adding a solution of KOH?
d. adding a solution of silver nitrate [silver sulfide (Ag2S) is insoluble]? |
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20 | |
Ozone (O3) and normal molecular oxygen (O2) transform into each other according to the reversible reaction
3O2 + energy ⇔ 2O3
How will the equilibrium be affected by increasing the temperature? Increasing the pressure? |
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21 | |
The reaction 2SO2 + O2 → 2SO3 is exothermic. How will a rise in temperature affect the yield of SO3 in an equilibrium mixture of the three gases? Will an increase in pressure raise or lower this yield? In what possible way can the speed of the reaction be increased at moderate temperatures? |
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22 | |
The three gases N2, O2, and NO are in equilibrium. The formation of NO is exothermic. Write the equation for the equilibrium. How would a decrease in temperature affect the equilibrium? A decrease in pressure? A lower concentration of N2? A lower concentration of NO? The presence of a catalyst? |
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23 | |
What class of reactions involves the transfer of electrons between the reacting substances? |
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24 | |
When an electric current is passed through a solution of hydrochloric acid, what substance is liberated at the anode (positive electrode)? At the cathode (negative electrode)? |
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25 | |
In each of the following reactions, identify the element that is oxidized and the one that is reduced:
Zn + Cu2+ → Zn2+ + Cu
Fe + 2H+ → Fe2+ + H2
Cl2 + 2Br- → 2Cl- + Br2
Cl2 + 2Fe2+ → 2Cl- + 2Fe3+ |
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26 | |
A displacement reaction is an oxidation-reduction reaction in which one element displaces another from solution. (a) In each of the following displacement reactions identify the element that is oxidized and the element that is reduced:
Zn + Cu2+ → Zn2+ + Cu
Fe + 2H+ → Fe2+ + H2
Cl2 + 2Br- → 2Cl- + Br2
(b) On the basis of the following displacement reactions, arrange zinc, iron, and copper in the order of their strength as reducing agents:
Zn + Cu2+ → Zn2+ + Cu
Fe + Cu2+ → Fe2+ + Cu
Zn + Fe2+ → Zn2+ + Fe |
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27 | |
Which loses electrons more easily, Na or Fe? Al or Ag? I- or Cl-? Which gains electrons more easily, Cl or Br? Hg2+ or Mg2+? |
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28 | |
Chlorine is a powerful oxidizing agent, which is the reason it is used as a bleach. Do you think a chlorine solution would remove a rust stain on a piece of clothing? |
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29 | |
How could you demonstrate that magnesium is a better reducing agent (that is, more easily oxidized) than hydrogen? |
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30 | |
What becomes of the electric energy provided in electrolysis? In what device is this energy transformation reversed? |
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31 | |
Why must water be added periodically to a lead-acid storage battery when it is in normal operation? |
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32 | |
A charging current is passed through a fully charged lead-acid storage battery. What happens? |
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33 | |
In what basic way is a fuel cell different from a dry cell or a storage battery? |
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