## Monatomic ideal gases

MaryBanh_2K
Posts: 101
Joined: Wed Sep 18, 2019 12:21 am

### Monatomic ideal gases

Can someone explain when to use the ideal gas constant for monatomic ideal gases? What is are some examples of a monoatomic ideal gas?

Selena Yu 1H
Posts: 108
Joined: Fri Aug 09, 2019 12:16 am

### Re: Monatomic ideal gases

You use the ideal gas constant for monoatomic ideal gases when you have constant pressure or constant volume. Some examples of monoatomic ideal gases include all the noble gases on the periodic table, like Xenon, Neon, etc.

Hannah Lee 2F
Posts: 117
Joined: Thu Jul 11, 2019 12:15 am

### Re: Monatomic ideal gases

Cv = 3/2R and Cp = 5/2R. This means that the molar heat capacity of a monoatomic ideal gas at a constant volume is 3/2R, and for constant pressure it is 5/2R. Both Cv and Cp are independent of T and P. You would use this when calculating enthalpy changes related to heating an ideal gas, and replace C in q = mCΔT or nCΔT with either Cv or Cp.

There is an equation deriving both Cv and Cp which you can find in Focus 4C, and Example 4C.1 shows you how to work through similar problems.

Examples include Ar(g), Xe(g), He(g), or any gas composed of a single atom. The only elements that are stable single atom molecules in nature are the noble gases.

For linear molecules like O2(g), Cv = 5/2R and Cp = 7/2R. The molar heat capacities of gases composed of molecules (not monoaatomic) are higher than those of monoatomic ideal gases because molecules can store E as more types of kinetic energy.