How to solve gas laws problems with the given "at STP" and with mass?

Question

how will i solve it?

and when the required is molecular weight/# of moles?

how to relate it with stoichiometry?

Answer 1

STP stands for Standard Temperature Pressure. The standard pressure is 1atm, and the standard temperature is 273 K. So, you already have 2 variables. As for the mass, you will have to convert it to moles. You do this by:

#grams osf substance * (1mol of substance/ mass of substance)

So, you will probably use the ideal gas law, because you are given T, P, n (number of moles), and you know R = 0.0821Latm/Kmol.

The only variable left to find is the volume (in L).

When the required is weight/# of moles, you are trying to find n. In this case, you will probably be given T, P, and V (R is a constant). You may also be given the density and the mass, and then you use

density = mass/volume to find the mass. And then you convert the mass to moles, and use in the formula if needed.

If it is related to stoichiomtry, then you will probably have an equation given. In which case, you would have to multiply number of moles, by the mole ratio of whatever molecule you wish to find.

Hope that helps! Good luck!