Question

6)What is heat of vaporization?

A.
It is the heat required to change a substance’s temperature by 1°C.
B.
It is the heat required to change a gram of substance from a solid to a liquid.
C.
It is the heat required to change a substance from a solid directly to a gas.
D.
It is the heat required to change a gram of substance from a liquid to a gas.
E.
It is the heat required to separate one substance into two substances.

7)
Why does every chemical reaction require a certain amount of activation energy?

A.
Energy is released when the reactants begin to react.
B.
Energy lost to the environment during the reaction must be replaced.
C.
Forming the activated complex requires energy.
D.
The products have more potential energy than the activated complex.
E.
The reactants have less potential energy than the products.

8)
A student places a 12-gram cube of ice inside a container. After six hours, the student returns to observe the contents of the container. Which sentence suggests that the container is an open system?
A.
The container contains 12 grams of liquid water and no ice.
B.
The container contains 12 grams of ice and no liquid water.
C.
The container contains 8 grams of liquid water and no ice.
D.
The container contains 8 grams of ice and 4 grams of liquid water.
E.
The container contains 8 grams of liquid water and 4 grams of water vapor.

9)An uncovered pot of water lies out in the sun. Which statements correctly describe what happens at the surface of the liquid water?

The vapor pressure remains constant regardless of the water temperature.
The vapor pressure is produced by water molecules that have evaporated.
The vapor pressure increases as the Sun heats the water in the pot.
Evaporation stops once the vapor pressure reaches a certain point.
Evaporation and condensation both occur on the liquid’s surface.
pick more then one for number 9

10)A man pours some hot coffee into a small cup from a large jug that contains enough coffee for several cups. Which statement correctly compares the coffee in the cup and in the jug?
A.
The coffee in the cup has a lower temperature than the coffee in the jug because there's less of it.
B.
The coffee in the jug absorbs more heat than the coffee in the cup because there's more of it.
C.
The coffee in the jug has more thermal energy than the coffee in the cup.
D.
The coffee in the cup and the coffee in the mug have the same amount of internal energy.
E.
The coffee in the cup has more thermal energy, but the coffee in the jug has more internal energy.

Answer 1

Six

A: Wrong: Anything that involves temperature is not going to describe the heat of vaporization.

B: Wrong: Vaporization has to do with gasses. Solids and liquids are not part of that process.

C: Wrong: C is describing sublimation, not vaporization.

D: Correct. That's the textbook definition.

E: Wrong. It is separating mixtures that can be separated by different temperatures where they boil.

Seven

I didn't like the wording of this question at all. The key word in the question is "Why" meaning why does it happen. The answer is what happens.

C: is the only possible answer. Some of the other answers are just taking up space (like A or B) and some are describing other events like D and E.

Eight

I wasn't fond of this one either, but at least the answer is reasonable. The key to understanding it is to realize that in an open system, it is possible for the energy to escape the system. This question is trying to trick you into answering a reasonable but made up answer.

A: if it is an open system, then why in an open system is it possible to have nothing left? There apparently is enough energy around that the ice goes from going from a solid to a liquid. That's no trivial amount of energy. A is wrong because there should be a loss of mass in the system. Some of the water has evaporated into the surroundings.

B: There has been too much time elapsed for B to be true. Think of a glass of water with ice in it. How long does it take for the ice to disappear? B is wrong.

C: I'd pick that as the answer. 4 grams have evaporated. That seems like a reasonable amount of time and a reasonable amount to have lost.

D: not possible. Refer to B

E: If you can detect the water vapor, you are not talking about an open system. And open system means that there is some way energy or (in this case) a gas can escape. E is incorrect.

Nine

This is again an open system.

This is the most open of all open systems.

A: wrong. If you add heat to the system, more molecules will have the required Kinetic (moving) energy to escape. That doesn't sound very constant to me.

B: could be true if the system was closed. Let's just hold on to this and see if we find two better answers.

C: Is a true statement, but I think it applies more to a closed system.

D: Wrong. This one really does require a closed system.

E: You are talking about equilibrium. That generally is true of a closed system which a topless pot is not (closed).

Try as I might, I can't come up with 2 answers I'm comfortable with. The two answers I would choose with a gun to my head is B and C. Be prepared to get the question wrong. It is so badly worded conceived that it is really hard to tell what to answer. (Sometimes you get that kind of answer from me). If someone contradicts, take their answer.

Ten

A is not true. At least when you first pour the cup. All water molecules are moving at roughly the same speed so the temperature is the same. The only difference is that the cup has a great big open end and the faster molecules (higher tempered ones) escape lowering the temperature of the cup of coffee.

B: is actually true if it is saying what I think it is saying. More molecules means more heat needed to raise the temperature of the the jug or even keep it constant.

C: I don't know how to distinguish B and C. Thermal energy is a form of KE or moving energy. If the jug has more it is because there is more of it.

D: Since internal energy occurs at the molecular level, that I think, is your choice. The temperature is the same for both.

E: internal energy occurs at the molecular level. It is not a macro event.

Thermal energy is a macro event. I don't think E is true.

I would pick D.

Answer 2

6) Heat of vaporization

D. is the heat required to change a gram of substance from a liquid to a gas .

Think of converting water (a liquid) of to steam (water vapor).

A. is the heat capacity of the substance.

B. is the heat of fusion.

C. is the heat of sublimation.

E. sounds like the heat of decomposition of a substance.

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7) Activation energy

C. Correct. Forming the activated complex requires energy.

A. Wrong. Energy is absorbed when the reactants begin to react.

B. Wrong. Energy lost to the environment has no effect on the activation energy. It just means that fewer molecules will have enough energy to get over the activation energy barrier.

D. Wrong. The products have less potential energy than the activated complex.

E. Wrong. The reactants may or may not have less potential energy than the products. It depends on whether the reaction is endothermic or exothermic.

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8) Open system

C. Correct. Heat must have come in from the surroundings to melt the ice and evaporate some of the water. The vapour could escape into the surroundings of the open container.

A. Wrong. This indicates a closed system, which can exchange energy but not matter with the surroundings.

B. Wrong. If the container contains 12 g ice and no water after 6 h, no heat energy has entered. The system is an isolated system.

D. Wrong. Heat has entered but mass is conserved. This is a closed system.

E. Wrong. Again, a closed system.

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9) Vapour pressure

B. Correct. The molecules that have escaped into the vapour phase create the vapour pressure. We measure the vapour pressure of a liquid in a closed system, but that is then the vapour pressure of the liquid whether the system is open or closed.

C. Correct. The vapour pressure increases as the temperature increases.

E. Correct. Evaporation and condensation both occur on the liquid’s surface, but not at the same rate in an open system. Most of the molecules that escape into the atmosphere will never return. However, a few molecules just above the surface may suffer collisions that send them back into the liquid.

A. Wrong. The vapour pressure increases as the temperature increases.

D. Wrong. Molecules are always escaping from the surface of the liquid.

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10) Heat, temperature and thermal energy

C. Correct. Thermal energy is an extensive property: it depends on how much of the substance you have. Thus, the coffee in the jug has more thermal energy than the coffee in the cup.

A. Wrong. The coffee in the cup should have the same temperature as that in the jug, at least at the moment of pouring. Temperature is an intensive property: it does not depend on the amount of substance.

B. Wrong. The coffee in the pot and in the jug are both hotter than the surroundings. They will lose heat to the surroundings.

D. Wrong. Internal energy is an extensive property.

E. Wrong. Thermal and internal energies are extensive properties.