help me please !!!

Question

Help!! I missed a whole week of school and didnt learn gas problems! Can you help me out with these practice questions??

Remember your pressure conversions: 1 atm = 14.7 psi = 760 mmHg = 101.3 kPa

- Remember any temperature in Celsius must 1st be converted into Kelvin by adding 273

- Remember that STP (standard temp and pressure) = 0 C or 273 K and 1 atm.

1. A balloon with a volume of 7.62 liters is containing 2.45 moles of gas. How many moles of gas remain if some gas is released and the balloon shrinks to a new volume of 5.25 liters (assume temp and pressure stay constant)

2. A 4.0 mole sample of gas occupies 4.4 liters at STP, which is 273 K and 1 atm. If more gas is added to the balloon, the volume increases to 6.7 liters and the number of moles is now 7.3 moles, and the pressure is now at 3.4 atm. What is the new temperature?

3. A sample of magic gas occupies 15.0 liters at 22 C and 754 mmHg. If the volume increases to 23.0 liters and the pressure drops to 723 mmHg, what’s the new temp?

4. A car tire has 65 moles of nitrogen gas (N2) and a volume of 87 liters. If the container has 776 more grams of N2 added, what will be the new volume of the tire? Hint: you need to determine convert grams into moles, and then add that to the original number of moles to get your 2nd number of moles.

5. A 12 liter tank contains 7 moles of oxygen. The pressure in the tank is 660 kPa at 25 C. If this oxygen tank were to leak, and lose 3 moles of O2 gas and the temperature now drops to 13 C, what would be the new pressure in the tank? Assume the volume of the tank stays the same at 12 liters.

Answer 1

I'm sorry that you missed school, but I'm not going to do all these problems. I will do a couple and hopefully get you started so that you can do the others. Good luck.

Start by memorizing the Ideal Gas Law which is PV = nRT

P = pressure in the appropriate units

V = volume in liters

n = moles

R = gas constant (usually 0.0821 Latm/Kmol) but there are other values with different units. Depends on units of pressure.

T = temperature in Kelvin

Also, from this Ideal Gas Law equation, you can derive all the other relationships, such as

P1V1 = P2V2

P1/T1 = P2/T2

P1V1/T1 = P2V2/T2

etc.

(1) V1 = 7.62 L

n1 = 2.45

V2 = 5.25 L

n2 = ?

Use V1/n1 = V2/n2

7.62 L/2.45 mol = 5.25 L/n2 mol

n2 = 1.69 moles left

(3) V1 = 15.0 L

T1 = 22ºC + 273 = 295 K (remember to always use Kelvin)

P = 754 mm Hg

V2 = 23.0 L

P2 = 723 mm Hg

T2 = ?

Use P1V1/T1 = P2V2/T2

rearrange and solve for T2:

T2 = P2V2T1/P1V1 = (723)(23)(295) / (754)(15)

T2 = 434K

If you want the new temperature in ºC, we subtract 273 to get 161ºC

Good luck with the others.