Annoying pressure prob. that is so easy i should not have to ask for help

[Rasine]

A child's helium-filled balloon escapes at sea level and 20.0°C. When it reaches an altitude of 2530 m where the temperature is 5.60°C and the pressure only 0.710 atm, what is the ratio its volume compare to that at sea level?


so i am going to use the ideal gas law... that is (p1v1)/t1=(p2v2)/t2

so if the gas is contained in a balloon, that means that the gas will still have the same amount of volume that it could fill so i am going to mulitiply v1 and v2 out so that i have

p1/t1=p2/t2

p1/293.15 K=0.710/ 278.75 K

p1=0.74667 atm

and now for the ratio...i am not sure if it is p1/p2 or p2/p1....but i think it may be p1/p2 and i get 1.05

either way i do the raito i still get the worng answer...please help me

 

[Dick]

If you are going to assume that the volume is unchanged, then there is not much point in computing a ratio of volumes, is there? Don't assume that and solve for v2/v1.