The ideal gas law

  • Thread starter kasse
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  • #1
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Homework Statement



When the volume of a gas is 2.81 L, the pressure is 740 Torr and the temperature is 20oC, how many moles of gas is there?

Homework Equations



PV=nRT

The Attempt at a Solution



740 Torr = 740*133.3 = 98.6*10^3 Pa
Temperature in Kelvin: 293 K

n = PV/RT = (98.6*10^3 * 2.81) / (8.3145*293) = 114 moles

The corret answer is 0.114 moles. Does this mean that when using the ideal gas law, the pressure should be in kPa?
 

Answers and Replies

  • #2
chemisttree
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What are your units for R? The pressure unit must match that.
 
  • #3
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J/(K*mol)
 
  • #4
Borek
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Does this mean that when using the ideal gas law, the pressure should be in kPa?
All it means is that units of data must match units of R.

R can take any value, it all depends on the units used. For example - 10.7316 ft3·psi·°R-1·lb-mol-1. Don't ask me what lb-mol is :smile:

Check how J/(K*mol) relates to pressure in kPa. What is Pa?
 
  • #5
chemisttree
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J/(K*mol)
Hint: "Oh, I thought it was in L kPa/mol K!"
 

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