Calculating Moles Using the Ideal Gas Law

[kasse]

Homework Statement

When the volume of a gas is 2.81 L, the pressure is 740 Torr and the temperature is 20^oC, 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?

 

[chemisttree]

What are your units for R? The pressure unit must match that.

 

[kasse]

J/(K*mol)

 

[Borek]

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

Check how J/(K*mol) relates to pressure in kPa. What is Pa?

 

[chemisttree]

J/(K*mol)

Hint: "Oh, I thought it was in L kPa/mol K!"