Number of moles of hydrogen gas in the cylinder

[mugen715]

Homework Statement

A gas cylinder contains 4.00 x 10^4 cm^3 of hydrogen at a pressure of 2.50 x 10^7 Pa and a temperature of 290 K. The cylinder is to be used to fill balloons. Each balloon, when filled, contains 7.24 x 10^3 cm^3 of hydrogen at a pressure of 1.85 x 10^5 Pa and a temperature of 290 K

Calculate the number of balloons that can be filled from the cylinder

Homework Equations

PV = nRT

The Attempt at a Solution

I try to find out the total number of moles of hydrogen gas in the cylinder

n = PV/RT
n = (2.50 x 10^7 x 0.04) / (8.31 x 290)
n = 415 moles of hydrogen in the gas cylinder

Since (PV/n) = RT = Constant

P1V1/n1 = P2V2/n2

Next i try to find out the number of moles of hydrogen in one balloon = n2

(2.5 x 10^7 x 0.04) / 415 = (1.85 x 10^5 x 0.00724) / n2

n2 = 0.556 moles of hydrogen in a balloon

The total number of balloons that can be filled up by this hydrogen gas is:

415 moles / 0.556 moles = 746 balloons

But the actual answer is 741 balloons, what wrong with my answer? could anyone figure out?

 

[Andrew Mason]

The total number of balloons that can be filled up by this hydrogen gas is:

415 moles / 0.556 moles = 746 balloons

But the actual answer is 741 balloons, what wrong with my answer? could anyone figure out?

Your answer is correct except this: how do you get the last tankful of gas (5.5 balloon-fulls) out of the tank and into the balloons at 185 kPa when the pressure in the tank is less than 185 kPa?

Welcome to PF by the way!

AM

 

[mugen715]

Okk..thanx you very much