G chem - When to use what R

[skyguy1]

Hey what are some equations where one R value is used over another...

I know it depends slightly on whats given to.. but for example for Pv=nrt its almost always the 0.08206

thanks

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[DAT Destroyer]

Hey what are some equations where one R value is used over another...

I know it depends slightly on whats given to.. but for example for Pv=nrt its almost always the 0.08206

thanks

For the DAT exam, they use R as 0.082. This is an easy number to work with, as we can often round it to be 0.1. In Physics, we usually deal with Pressure units in the SI unit called the Pascal.....In cases like that, we have R=8.314. For the DAT, surely R will be the former, 0.082 to make the calculations quick and easy. Sometimes R is 1.99 when doing work in calories. Most chemists and people who develop General Chemistry problems use the 0.082 constant.

Hope this helps

Dr. Jim Romano

 

[StudentDoc1234]

Hi,

I was wondering, on a given question where R is needed to be used to answer the question, will R be given to us on the DAT?

 

[DAT Destroyer]

When pressure is in atm, volume is in liters and temperature is in kelvin. You will use the value .0821 for the DAT. If you want to discuss other possible units in which r is a different value I will be happy to explain it but it is not likely to be on the DAT.

Dr. Romano

 

[100%permwinner]

Depending on the question. If the question has to do with gases, R = 0.0821 atmL/molK. Note 1 atm = 760 torr = 760 mmHg
If the question asks to find the value of Gibb's free energy ΔG = RTlnK (equilibrium constant) or activation energy Ea = RTln k (rate constant), use R = 8.314 J/molK.

 

[StudentDoc1234]

Thank you!