How do we know which gas constant to use?
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How do we know which gas constant to use?
In the equation sheet, multiple values are listed for the ideal gas constant (with different units). I've always used .08206 L·atm·K-1·mol-1 as the gas constant in previous classes, but this example in lecture used 8.314 J·K-1·mol-1. Is this because we aren't given volume in liters or perhaps because we're solving for volume?
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Re: How do we know which gas constant to use?
The ideal gas constant used depends on the units provided in the question and are using to solve the question. If the question uses L and atm, you will probably use 8.206*10^-2 L*atm/K*mol and if the question uses J, you'd use 8.314J/K*mol. In the example from lecture today, 8.314J/K*mol was used for R because the enthalpy was given in kJ. There was no mention of liters in the question so I would just stick to the units given in the problem to see which gas constant to use.
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Re: How do we know which gas constant to use?
Similar to what Harsimer said you have to see which gas constant has the units that will allow it to cancel out others given in the problem.
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Re: How do we know which gas constant to use?
It is safe to assume that we will be using the J/K*mol constant for the ideal gas law. Otherwise you should check which units are present in order to use the right one.
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Re: How do we know which gas constant to use?
To figure out what gas constant to use, you can check the units of the other values and use the gas constant with those units. This way, units can cancel out.
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Re: How do we know which gas constant to use?
I believe for at least the midterm it should be given!
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Re: How do we know which gas constant to use?
I would assume the gas constant will be given, but if not, check the units of of the units given/calculated and match the gas constant to it.
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Re: How do we know which gas constant to use?
The gas constant that you use should match the units used in the problem. Therefore, if the units are L and atm, you will use 8.206*10^-2 L*atm/K*mol and if the units are J, you will use 8.314J/K*mol
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Re: How do we know which gas constant to use?
Just make sure that the units of the gas constant correspond to those given in the problem, so that they may cancel out.
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