# pressure/ temp/ volume

Discussion in 'DAT Discussions' started by Dencology, Jun 3, 2008.

1. ### Dencology 2+ Year Member

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guys, i keep getting is concept wrong.

if pressure is quartered and temp double, by what factoer , volume change?
it is 8 right?

now what if pressure doubled, volume tripled, now by what factor temp changes? (if n and R are constant)
is is 6 ----> PV=T
(2)(3)= 6

2. ### osimsDDS 5+ Year Member

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you cant do that, pressure and volume are inversely related....so if pressure increases volume has to decrease by the same amount to keep it constant...PV=k (constant).

Ex/ If pressure doubled, volume would have to be decrease by half to compensate for consistency...

3. ### baedero1 2+ Year Member

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PV/T=K

1/4P*V / 2*T =K ---> V should be 8

(2*P)(3*v)/T = K ----> T have to be decreased by 1/6

4. ### osimsDDS 5+ Year Member

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The first one you can do, the second example you gave you cant do thats what i meant....sorry

5. OP

### Dencology 2+ Year Member

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so you would say that the example i gave does not work.? if pressure is increased by a factor of 2 and temperature is increased by a factor of 4, what should be the factor of volume to keep everything constant?

6. ### osimsDDS 5+ Year Member

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ok this can work....Pressure by a factor of 2 and Temp. by a factor of 4.

So if pressure increased by a factor of 2 then Volume has to decrease to make it constant by a factor of 1/2. Then if Temp. increased by 4 then volume would have to be increased by 4 as well since they are proportional.

so: 4 x 1/2= 2

The key is to know what relates to what and how they change according to the constants...take each by itself. For example try to do it the other way starting with temp and volume first...

since temp is increased by 4 so does volume increase by 4. Then if pressure is increased by 2 then volume has to decrease by the same amount (1/2)...So you see its exactly the same if you start with either one...

7. ### Shjfr 5+ Year Member

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You can just relate everything to the original equation, this makes it pretty easy.

Original equation:
PV=nRT

New equation:
(2)PV=nR(4)T

Divide the 4 over: (1/2)PV=nRT

So, V must be 2 times larger to get it back to the original equation

8. OP

### Dencology 2+ Year Member

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i like how you explained. now to cement everything together, would you give a problem in the same realm?

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