Does the amount of molecules of gas change at a temp lower than STP? the temperature is 175 K.

Question

anonymous · Answer

Urgent have Finals tomorrow.

photon336 · Answer

Well, @Clemsongator at lower temperatures gas molecules would be moving around much more slowly.

photon336 · Answer

but in terms of the amount of gas, generally it would be constant.

anonymous · Answer

so the amount would be about the same as STP?

photon336 · Answer

Yeah, remember you said lower temperature. 

The lower the temperature, the slower the gas molecules move. remember temperature = the average kinetic energy, of the particles. 0.5mv^2. 

let's look at the ideal gas equation. 

pV = nRT 

usually the number of moles of gas n and R are usually constants.

anonymous · Answer

okay so if  have 24.23L of nitrogen monoxide at STP I would still have that amount?

anonymous · Answer

okay

photon336 · Answer

$$\frac{ 1 mol of any gas  }{ STP } =  22.4L $$

photon336 · Answer

if we change the temperature, the volume that the gas will occupy will be different, but the number of moles will be the same.

anonymous · Answer

okay the question wants to know how many molecules would be in the sample at 175K

photon336 · Answer

okay let me see

photon336 · Answer

okay so if  have 24.23L of nitrogen monoxide at STP.

So sw know at STP 1 mol of any gas occupies 22.4L right? so our gas occupies 24.32 liters so it must be a little bit over 1 mole. 

see below. we setup a porportion. 

$$\frac{ mol }{ 22.4L  } = \frac{ x }{ 24.32L } = \frac{ 24.32 }{ 22.4  }  = 1.1 mol, of NO$$


okay the question wants to know how many molecules would be in the sample at 175K, 

This is our inforamtion that we have. 

273K, 1atm, 1.1 mol, 24.32L 

when we lower the temperature, we may cause a change in the pressure or volume, but not the number of moles. to do calcualtions with that equation we must keep one of the variables constant. 

pV = nRT essentially the number of moles should be the same. 

essentially this equation rests on the fact that we study changes in pressure temperatuer and volume, with the idea that the number of moles is constnat.

anonymous · Answer

Thanks

photon336 · Answer

@clemsongator np