Calculating Grams of Helium Needed for Blimp to Rise

In summary, when 1.10 mol of helium is added to a blimp, the volume is 26.2 dm^3. To make the blimp rise, 1.10 more grams of helium must be added.
  • #1
Myung
42
0

Homework Statement



Blimps are being considered for use as freight carriers. A scale model rises when filled with helium to a volume of 55.0 dm3. When 1.10 mol He is added to the blimp, the volume is 26.2 dm3. How many more grams of He must be added to make it rise? Assume constant T and P. (4.003 g He = 1 mol He)

Homework Equations



PV = nRT
R = 0.8206 ( litres-atm/mole-K )
1 dm^3 = 1L

The Attempt at a Solution



Required volume to fill is 28.8 dm^3 or L

PV = nRT

Assume T and P is constant?
How do we do that? That is my question.
 
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  • #2
Myung said:

Homework Statement



Blimps are being considered for use as freight carriers. A scale model rises when filled with helium to a volume of 55.0 dm3. When 1.10 mol He is added to the blimp, the volume is 26.2 dm3. How many more grams of He must be added to make it rise? Assume constant T and P. (4.003 g He = 1 mol He)

Homework Equations



PV = nRT
R = 0.8206 ( litres-atm/mole-K )
1 dm^3 = 1L
You are trying to find n. You want to express n as a function of V. If P and T are constant, what is the relationship? How would you find P/RT (which is constant) from the information provided?

AM
 
  • #3
Andrew Mason said:
You are trying to find n. You want to express n as a function of V. If P and T are constant, what is the relationship? How would you find P/RT (which is constant) from the information provided?

AM

They are inversely proportional to each other ( P and T ) ,

Universal Gas Constant = 8.206 ( Litres - atm / mole - K )

n = PV/RT

1 atm is the constant Pressure at sea level but I don't know the temperature?
 
  • #4
bump!
 
  • #5
Myung said:
They are inversely proportional to each other ( P and T ) ,

Universal Gas Constant = 8.206 ( Litres - atm / mole - K )

n = PV/RT

1 atm is the constant Pressure at sea level but I don't know the temperature?

You don't need to know the pressure or temperature; It's enough to know that they are constants.

In your expression for n above, group all the constants together and replace them by a single new constant. Let's call it k. Now, in the problem statement you're given a particular case for n and V. Find k from that particular case. You can then use this k value to proceed.
 
  • #6
gneill said:
You don't need to know the pressure or temperature; It's enough to know that they are constants.

In your expression for n above, group all the constants together and replace them by a single new constant. Let's call it k. Now, in the problem statement you're given a particular case for n and V. Find k from that particular case. You can then use this k value to proceed.

P/T = nR/V

Let P/T = k

k = nR/V

Given the case that there are 1.10 moles in 26.2 dm^3/L of He

k = [1.10moles ( 0.8206 ) L-Atm/moles-K] / 26.2L of He

k = 0.03445267176 Atm/Kelvin

Constant value gained!

n = V/R * (k)

n = 28.8 L / 0.8206 Litres-atm/mole-kelvin * ( 0.03445267176 Atm/Kelvin )

n = 1.21 moles

1 mole = 4.003 g HE

He = 4.84 Grams.

THANKS!
 

1. How do you calculate the grams of helium needed for a blimp to rise?

To calculate the grams of helium needed for a blimp to rise, you need to know the total weight of the blimp (including the weight of the envelope, gondola, and any additional equipment), the weight of the air that the blimp will displace, and the density of helium. The formula is grams of helium = (total weight - weight of displaced air) / density of helium.

2. What is the density of helium?

The density of helium is 0.1785 grams per liter at standard temperature and pressure (STP). This may vary slightly depending on the temperature and pressure at which the blimp will be flying.

3. How does the size and shape of the blimp affect the amount of helium needed?

The size and shape of the blimp can greatly affect the amount of helium needed. A larger blimp will require more helium to lift its weight, while a more streamlined shape will reduce the amount of air the blimp displaces, thus reducing the weight of the displaced air that needs to be accounted for in the calculation.

4. Are there any other factors to consider when calculating the grams of helium needed for a blimp to rise?

Yes, there are other factors that can affect the amount of helium needed for a blimp to rise, such as the altitude at which the blimp will be flying, the temperature and pressure at that altitude, and any additional weight that may be added to the blimp during flight (such as fuel or cargo).

5. What happens if the calculated grams of helium needed are not enough for the blimp to rise?

If the calculated grams of helium needed are not enough for the blimp to rise, the blimp will not be able to take off or it will not be able to maintain its desired altitude. This can be dangerous and potentially result in a crash. It is important to accurately calculate the necessary amount of helium to ensure safe flight.

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