A helium balloon has a volume of 2.5 L. When heated to 343.5K the pressure of the gas is 66.7 kPa. How many moles of He gas would there be?

0.06mole

Explanation:

Given parameters:

Volume of balloon = 2.5L

T = 343.5K

P  = 66.7kPa; in atm  gives  = 0.66atm

Unknown:

Number of moles of He  = ?

Solution:

To solve this problem, we use the ideal gas equation.

 It is mathematically expressed as;

               Pv = nRT

  where  p is the pressure

              v is the volume

               n is the number of moles

               R is the gas constant

               T is the temperature

      0.66 x 2.5  = n x 0.082 x 343.5

                      n  = 0.06mole

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.