Thermodynamics is concerned with changes in the properties of matter

Question

Thermodynamics is concerned with changes in the properties of matter when we alter the external conditions. An example of this is a gas being compressed by the motion of a piston. The final outcome depends on how the change is made—if the piston is moved in slowly, we say that the compression is “reversible.” This means that if we pull the piston back out, we retrace the same sequence of properties but in the reverse order; hence, the temperature of the gas will be the same when the piston has been pulled out as it was before the piston was pushed in. However, if the piston is moved in and out quickly, then the initial state (and temperature) will not be recovered—the gas will always be hotter than it was at the beginning.  This is a manifestation, although not a statement,  of the second law of thermodynamics. It also makes a difference whether there is a transfer of heat between the cylinder of gas and the external surroundings. If the cylinder is insulated, then the gas will heat on compression and cool on expansion (refrigeration uses this principle). On the other hand, if the cylinder can exchange heat with the surroundings, it will remain at the same temperature if the compression is slow enough.   1 
 1. The scope of this passage is

A. the motion of a piston demonstrating the effects of thermodynamics.
B. the conservation of heat during the motion of a piston.
C. how the second law of thermodynamics applies to pistons.
D. how thermodynamics function.
E. reversible compression.

2 
 2. Based on this passage, if we were to record the temperature of the gas within a cylinder of a car engine when we were driving the car at 20 mph, and measure it again after accelerating the car to 40 mph (thus speeding up the piston), what would we expect to find?

A. The gas would be hotter in the first reading.
B. The gas would be hotter in the second reading.
C. The gas would be the same temperature in both readings.
D. There is no way to accurately predict the change in temperature.
E. The gas would be cooler in the second reading if the engine were well insulated.

3 
 3. Given the context, what is the meaning of the highlighted phrase?

A. The second law of thermodynamics is only applicable to objects moving at high speeds.
B. The motion of the piston is a confirmation of the second law of thermodynamics.
C. The second law of thermodynamics cannot, on its own, explain the change in heat in the cylinder.
D. The change in heat inside the cylinder illustrates the second law of thermodynamics but does not prove it.
E. The motion of the piston disproves the second law of thermodynamics.

Sajjad1994 · Answer

OE

1. The scope of this passage is

Explanation

Remember, the first thing to do with any passage is to identify the topic and the scope. The topic is the broad subject of the passage—in this case  “thermodynamics.”  You can immediately rule out  (D)  because it speaks of the topic rather than the scope. The scope of the passage focuses on the application of thermodynamics to the motion of a piston, which is what answer  choice (A)  states—it is the correct answer.

Choices (B), (C),  and  (E)  refer to specific subjects mentioned in the passage but do not refer to the passage as a whole.

Answer: A

Sajjad1994 · Answer

OE

2. Based on this passage, if we were to record the temperature of the gas within a cylinder of a car engine when we were driving the car at 20 mph, and measure it again after accelerating the car to 40 mph (thus speeding up the piston), what would we expect to find?

Explanation

The passage informs you that the faster a piston is moving in and out of a cylinder, the hotter the gas will become. Based on this, you can infer that the when the car is moving faster, the gas will become hotter because the pistons will be moving more quickly. Thus, the correct answer choice is  (B) . Even if you are unsure of the concepts described in a passage, sometimes you can make a reasonable guess at an answer based on common sense. In this case, you can assume that the parts of a car’s engine will be hotter when the car is going faster without having to apply what you have learned in the passage about thermodynamics.

Answer: B

Sajjad1994 · Answer

OE

3. Given the context, what is the meaning of the highlighted phrase?

Explanation

The key contrast to make note of here is the difference between  “manifestation”  and  “statement” —that is, the difference between an appearance of something and a declaration of it. What the highlighted phrase, then, says is that the motion of the piston is an appearance—an example, if you will—of the second law of thermodynamics but it is not an explanation or proof of it.

Choice (A)  you can reject because a universal law is not applicable only to certain circumstances.

While  (B)  might suggest an excellent example to demonstrate the second law of thermodynamics, it is not proof of it—(B) is, in fact, the opposite of our desired answer; furthermore, it would be a poorly worded answer in that it suggests the second law of thermodynamics relates to the physical object of the piston rather than the gas within the cylinder.

(C)  is also inaccurate because the highlighted phrase tells us that the change in heat in the cylinder is an example of the second law of thermodynamics.

Answer  choice (D) , however, states that the change in heat is an example rather than a proof of the second law of thermodynamics, and this is the correct answer.

Finally, since the highlighted phrase refers to an example of the second law of thermodynamics, it certainly doesn’t disprove that law, so  (E)  is wrong.

Answer: D

Thermodynamics is concerned with changes in the properties of matter

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