2007 ada question 46 ???

[wired202808]

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When the volume of a gas is Decreased at constant temperature, the Pressure increase because molecules:

a. move faster
b. move slower
c. become heavier
d. become lighter
e. strike a unit area of the container more often

the answer is E however, why cant it be B? since the volume is now less and the pressure is more aren't molecules simply moving slower or less as they are compressed down by the pressure? I understand that they do strike the container more but how would that affect pressure?

How should I be analyzing this problem? from the viewpoint of volume or pressure?

Thanks guys.

 

[wizi]

For me, I use this formula

PV = nRT --> P = nRT/V. nRT is constant because T is constant --> decrease V = increase P.

Because our T is constant, gases speed doesn't change.

 

[AlbinoPolarBear]

When the volume of a gas is Decreased at constant temperature, the Pressure increase because molecules:

a. move faster
b. move slower
c. become heavier
d. become lighter
e. strike a unit area of the container more often

the answer is E however, why cant it be B? since the volume is now less and the pressure is more aren't molecules simply moving slower or less as they are compressed down by the pressure? I understand that they do strike the container more but how would that affect pressure?

How should I be analyzing this problem? from the viewpoint of volume or pressure?

Thanks guys.

Molecules moving faster or slower is dependent on the temperature, and not the volume or pressure.

When the numbers of molecules stay constant, but the volume decreases, there will be 'less room' for the molecules to move around, so they will collide with the container more often.

Think of 10 people at a party, and they are in the living room. Walking around. There's a lot of space and people move around pretty freely.
Then all of those 10 people go a small washroom together. ALL of them. Then they walk around. There's not gonna be that much space in the washroom. And they will hit the wall more often. Increasing the 'pressure'.

 

[wired202808]

Molecules moving faster or slower is dependent on the temperature, and not the volume or pressure.

When the numbers of molecules stay constant, but the volume decreases, there will be 'less room' for the molecules to move around, so they will collide with the container more often.

Think of 10 people at a party, and they are in the living room. Walking around. There's a lot of space and people move around pretty freely.
Then all of those 10 people go a small washroom together. ALL of them. Then they walk around. There's not gonna be that much space in the washroom. And they will hit the wall more often. Increasing the 'pressure'.

thanks bear! awesome explanation! makes a ton of sense now that I take temp into consideration.

I was comfortable with pv=nrt but was stuck between the various choices but its good to remember what makes sense!