Ideal Gas Equation/Molar & Molecular Mass Thermal Physics Lesson 4

Learning Objectives Define a mole Calculate the number of moles in a gas using N=nN A Perform calculations using the ideal gas equation pV=nRT Describe the conditions for which a real gas behaves like an ideal gas

Avogadro’s Constant One mole of any gas contains the same number of particles. This number is called Avogadro’s constant and has the symbol N A. The value of N A is 6.02 × particles per mole.

Calculating the Number of Moles The number of moles, n, of a gas can be can be calculated using:- Where N is the total number of molecules and N A is Avogadro’s constant (=6.02 × )

Avogadro’s Law The most significant consequence of Avogadro's law is that the ideal gas constant has the same value for all gases. This means that the constant is given by:-

Deriving Ideal Gas Equation From Boyle’s Law: From Pressure Law: From Avogadro’s Law: Combining these three: Rewriting using the gas constant R: Therefore:-

The Ideal Gas Equation Combining the three gas laws gives the equation:- The constant is equal to nR. Works well for gases at low pressure and fairly high temperatures

Equation of State Recall that each phase can exist in a variety of states e.g. the temperature and pressure Thus the Ideal Gas Equation of State pV = nRT summarises the physically possible combinations of p, V and T for n moles of the ideal gas.