If a 30-ft volume of air at 10 psig is compressed to 25-ft at a constant temperature what would be the new pressure in psig?

Answer 1

First of all, "30-ft" and "25-ft" are not volumes, so I'll have to assume, on your behalf,

that you meant "cubic ft".

If you're in a class where this has been assigned, let's say, as a homework exercise,

then the class has already learned that at constant temperature, volume of gas is

inversely proportional to pressure. In other words, for example, if you need to compress

some gas into half the volume, you need to squeeze twice as hard.

If you massage this characteristic of gas with some algebra ... a simple process, for which

we don't have the time just now ... you discover that it also means that the product of

(pressure) times (volume) is always the same number, as long as the temperature of

the sample of gas doesn't change.

So P1V1 = P2V2 . That's the math, and three of these four quantities are listed in the question.

(10) x (30) = (P) x (25)

You certainly ought to be able to perform the final step, and pull the new pressure out of that.

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OK. Just remember that (Pressure) x (Volume)/(Temperature) remains a constant number

for a sample of gas, as long as none is added and none leaks out. If any one of the

three numbers changes, the others have to change in just the right way to keep the

whole fraction the same number.

Also remember that the 'temperature' in that expression is the 'absolute' temperature,

measured from absolute zero. So it's the number of Celsius degrees above -273, or the

number of Fahrenheit degrees above -460 .

That's enough to give you a good solid start. Good luck.

*12 was the wrong answer..... I forgot to add 14.696 to the org. 10psi for a psia measure.....which changed the mutiplication......the right answer was 14.939 because you subtract psia after the division, thanks for your help......To think, these are just the basics......

Answer 2

The Universal Gas Law says (P * V / T) is a constant.

In the problem, the temperature information is not given, so is assumed to be the same before and after. So, the Gas Law becomes (P * V) = constant.

Hence, P1V1 = P1V2 ----- (1),

where P1 and V1 are the original gas pressure and volume, respectively; P2 and V2 are the final gas pressure and volume, respectively.

Given: P1 = 35 psig; V1 = 50 ft3; V2 = 25 ft3.

Procedure:

Substituting the given information in equation (1), we get

P2 = (P1 * V1 / V2) = 35 * 50 / 25 = 70 [psig]

Q.E.D.

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Answer 3

Using Boyle's Law (P1V1 = P2V2), the new pressure can be calculated as follows:

P1 = 10 psig V1 = 30 ft V2 = 25 ft

P2 = (P1 * V1) / V2 P2 = (10 psig * 30 ft) / 25 ft P2 = 12 psig

Therefore, the new pressure would be 12 psig.