PV=NRT

[Lizzy Pearl]

Question:

if you want to increase the kinetic energy of molecules initially at 20 c and a pressure of 1 atm without changing the volume you will.....

a) increase temp;
b) decrease temp
c) decrease pressure
d) double both the temp and pressure

The answer is increase temp. I'm confused.... if you increase the temp, won't that also increase the volume? Shouldn't you change the temp and pressure to keep the volume unchanged?

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[Bareitashvilli]

Question:

if you want to increase the kinetic energy of molecules initially at 20 c and a pressure of 1 atm without changing the volume you will.....

a) increase temp;
b) decrease temp
c) decrease pressure
d) double both the temp and pressure

The answer is increase temp. I'm confused.... if you increase the temp, won't that also increase the volume? Shouldn't you change the temp and pressure to keep the volume unchanged?

That is what I thought too when I saw it.
That is in accordance with Charle's law.
Something is happening in the situation that makes it not that way. (Charle's law situation)

20 degrees Celsius
1 atm

PV = nRT
We know that doubling temperature and pressure changes nothing. Pressure decreases volume so the gas would have less room to move so it would have little energy.

Decreasing temperature makes it colder so less energy.
Decrease pressure you increase the volume that only means more space for the molecules to move not more energy.

But making it hotter makes the molecules go faster. Therefore this is the correct answer.

 

[Lizzy Pearl]

Ok...so focus on the energy aspect of the problem. Thanks!

 

[DagS132]

This may sound stupid but what I am thinking is that this reaction is occurring in a closed system. So imagine a box that can't be expanded or compressed where the reaction is occurring. Volume won't increase but the pressure will when increasing temperature.