How many moles of gas are in the balloon?

roam

1. Homework Statement

A spherical balloon is inflated to a diameter of 36 cm. Assuming that the gas in the balloon is of atmospheric pressure (101.3 kPa) and is at a temperature of 20°C.

(a) How many moles of gas are in the balloon?

(b) If 21% of the molecules in the balloon are oxygen molecules, how many oxygen molecules are in the balloon?

3. The Attempt at a Solution

(a) I want to use the formula $$PV=nRT$$

Volume is $$v=\frac{4}{3} \pi (0.18)^2 = 0.1357$$

R is the constant 8.314

So $$(101.3)(0.1357)=n8.314(20)$$

Now if I solve for n I get $$n= {13.74}{166.28} = 0.082$$

This is wrong because the correct answer must be 1.02. Do I need to convert the temprature to Kelvin/absolute temprature? ...because I tried that too & it didn't work.

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rl.bhat

Homework Helper
Given pressure is in kilopascal.
Temperature must be in Kelvin.

Last edited:

mgb_phys

Homework Helper
Temperature should be in kelvin

rock.freak667

Homework Helper
Your temperature should be in Kelvin (K) and the pressure in Pa

roam

Okay 20 degrees is 293.15 in Kelvin, and I converted the pressure to pascals. So my equation becomes

$$(101300)(0.1357)=n(8.314)(293.15)$$

n= 5.64

But why is this still not the right answer? rl.bhat

Homework Helper
Okay 20 degrees is 293.15 in Kelvin, and I converted the pressure to pascals. So my equation becomes

$$(101300)(0.1357)=n(8.314)(293.15)$$

n= 5.64

But why is this still not the right answer? Check the volume of the gas.
V = 4/3*π*r^3

inutard

= [. I said that earlier. I'm sad now.

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