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# Chemistry Questions, Calculating Volume?

A sample of helium gas occupies 12.4 L at 23 °C and 0.956 atm. What volume will it occupy at 40 °C and 0.956 atm?

a. 21.6 L

b. 11.7 L

c. 7.13 L

d. 13.1 L

A gas has a volume of 5.0 L at a certain pressure. How must the pressure be changed to double the volume of the gas at constant temperature?

a. There is not enough information to decide.

b. The pressure must be doubled.

c. The pressure must be quadrupled.

d. The pressure must be halved.

A gas occupies 30. L at 2.0 atm pressure and 27 °C. Calculate the volume of the gas if the pressure remains at 2.0 atm, but the temperature is raised to 54 °C.

a. 12 L

b. 33 L

c. 86 L

A gas occupies 30. L at 2.0 atm pressure and 27 °C. Calculate the volume of the gas if the pressure is decreased to 1.0 atm at constant temperature.

a. 79 L

b. 15 L

c. 60. L

Thanks, for any help!

### 2 Answers

- 3 years agoFavorite Answer
P1V1/T1 = P2V2/T2

Temp must be in K .. (K = °C 273)

1)A sample of helium gas occupies 12.4 L at 23 °C and 0.956 atm. What volume will it occupy at 40 °C and 0.956 atm?

T1= 273 23 = 296, T2 = 273 40 = 313

P1V1/T1 = P2V2/T2

The pressure is constant @ .956 atm

V1/T1 = V2/T2

V2 is the unknown

V2 = V1T2/T1

V2 = (12.4L)(313K)/296K

V2 = 13.1L (d)

2)A gas has a volume of 5.0 L at a certain pressure. How must the pressure be changed to double the volume of the gas at constant temperature?

a. There is not enough information to decide.

b. The pressure must be doubled.

c. The pressure must be quadrupled.

d. The pressure must be halved.

P1V1 = P2V2

You want the volume to increase from 5L to 10L

P2 = P1V1/V2

P2 = (x)(5)/10

P2 = 5x/10

P2 = .5x

The pressure x must be multiplied by (.5) or halved ... (d)

3) A gas occupies 30. L at 2.0 atm pressure and 27 °C. Calculate the volume of the gas if the pressure remains at 2.0 atm, but the temperature is raised to 54 °C.

Pressure is constant

T1 = 273 27 = 300

T2 = 273 54 = 327

V2 = V1T2/T1

V2 = (30L)(327K)/300

V2 = 32.7L (b)

4) A gas occupies 30. L at 2.0 atm pressure and 27 °C. Calculate the volume of the gas if the pressure is decreased to 1.0 atm at constant temperature.

P1V1/T1 = P2V2/T2

Constant temp

V2 is the unknown

V2 = V1P1/P2

V2 = (30L)(2 atm)/1 atm

V2 = 60L (c)

Once you know the formula: P1V1/T1 = P2V2/T2

You have to determine what value is your unknown, then solve for your unknown.

Write out the equation ---> P1V1/T1 = P2V2/T2

If you wanted to solve for T2 ...

1st you would cross multiply:

P1V1T2 = P2V2T1

then, once your variables are in a straight line (you cross multiplied to get rid of the fractions). Now, in order to solve for (or isolate) T2 you would divide both sides of the equation by P1V1 --->

P1V1T2/P1V1 = P2V2T1/P1V1

P1V1 cancels on the left, leaving:

T2 = (P2)(V2)(T1)/(P1)(V1)

Any values that remain constant can be ignored.

It's all about re-defining the equation in terms of your unknown. Then your calculator does all the work.

make sure you convert Celsius to Kelvin ...

I hope that helps, good luck.

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- Roger the MoleLv 73 years ago
(12.4 L) x (40 + 273) K / (23 + 273) K = 13.1

So answer d.

d. The pressure must be halved.

(30. L) x (54 + 273) K / (27 + 273) K = 33 L

So answer b.

(30 L) x (2.0 atm / 1.0 atm) = 60 L

So answer c.

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