which gas has molecules with the greatest average molecular speed at 25 C?

2 Answers

• average speed = square root of (8RT/pi M)

  where R = gas constant = 8.314 J/K/mole

  T = temperature

  pi = 22/7 or 3.14

  M = molecular mass

  now since mass is in denominator ....it means molecular mass is inversely proportional to average speed ....so as mass increases average speed decreases.....and as mass decreases average speed increases

  so find out -which of the following has lightest molecular mass

  CH4 = 16 g/mole

  Kr = 83.8 g/mole

  N2 = 28 g/mole

  CO2 = 44 g/mole

  Ar = 39.9 g/mole

  since CH4 has lowest molecular mass among these so it's average speed will be highest...

  and the order of average speed for these gases in decreasing order will be :

  CH4 > N2 > Ar > CO2 > Kr

• CH4 because its molar mass is the smallest