Themes > Science > Chemistry > Inorganic Chemistry > More Information About Gas Laws > Gas Index > Ideal gas law

It is possible to combine the laws that describe the relationships between volume and temperature (Charles's law), volume and pressure (Boyle's law) and the knowledge that the volume of a gas is directly proportional to the amount of gas into one simple relationship, the Ideal Gas Law
PV = nRT
Here, P is pressure, V is volume, T is temperature, n the number of moles of gas and R the ideal gas constant.

 

Despite its simplicity, this law is remarkably good at predicting the behavior of real gases at ordinary temperatures and pressures. Once you know three of the four properties of a gas (P,V,T,n), you can compute the fourth easily. Moreover, this law applies to almost all gases: even though argon is a noble gas and nitrogen is a diatomic molecule, they both still obey the ideal gas law quite well.

Example: What is the volume occupied by a 10 gram sample of nitrogen gas at 25oC and 1.0 atm pressure?

Solution: We are given P and T. We need to compute n, the number of moles of gas. Nitrogen gas has the formula N2 and thus a molecular weight of 28 g/mole, so we have

10 g /28 g/mole = 0.36 moles of nitrogen gas
We look up the value of R in units that we can use for this problem: the best is R = 0.0821 (L*atm)/(mol*K), since this uses atmospheres for our unit of pressure. We need Kelvin temperature, so T = 25 + 273 = 298 K. We now have all the pieces we need.
PV = nRT
1.0 atm * V = 0.36 mole * 0.0821 (L*atm)/(mol*K) * 298 K
1.0 atm * V = 8.8 L*atm
V = 8.8 L


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