text: # Problem: Olympic cyclists fill their tires with helium to make them lighter. Assume that the volume of the tire is 860 mL , that it is filled to a total pressure of 125 psi , and that the temperature is 25 oC. Also, assume an average molar mass for air of 28.8 g/mol.What is the mass difference between the two?
  
  ###### FREE Expert Solution
  
  Calculate the moles of that can occupy the tire:
  
  $\mathbf{PV}\mathbf{=}\mathbf{nRT}\phantom{\rule{0ex}{0ex}}\frac{\mathbf{PV}}{\mathbf{RT}}\mathbf{=}\frac{\mathbf{n}\overline{)\mathbf{RT}}}{\overline{)\mathbf{RT}}}\phantom{\rule{0ex}{0ex}}\overline{)\mathbf{n}\mathbf{=}\frac{\mathbf{PV}}{\mathbf{RT}}}$
  
  T = 25°C +273.15 = 298.15 K
  
  V = 0.860 L
  
  P = 8.6058 atm
  
  n = 0.299 mol ≈ 0.30 mol
  
  Calculate the mass of helium (He) and air:
  
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  ###### Problem Details
  
  Olympic cyclists fill their tires with helium to make them lighter. Assume that the volume of the tire is 860 mL , that it is filled to a total pressure of 125 psi , and that the temperature is 25 oC. Also, assume an average molar mass for air of 28.8 g/mol.
  
  What is the mass difference between the two?