[[Thermodynamics MOC]]
# Ideal gas
An ideal gas is an _idealised_ gas for which the following assumptions hold:

1. Newton's laws apply to the particles
2. The particles are identical and have effectively zero volume.
3. The particles are constantly engaged in random motion with a distribution of speeds independent of direction ([[Brownian motion]]).
4. There is no attraction or repulsion between gas particles or their surroundings.
   Therefore, there is no $E_P$, only $E_K$.
   Collisions between particles and the container walls are the only forces on the particles.
5. All collisions are _elastic_, i.e. no $E_K$ is lost.

One set of thermodynamic equations of state for an ideal gas are

1. [[Ideal gas law]] ($pV = \nu RT$)
2. [[Energy of an ideal gas]] ($E = \alpha\nu RT$)

## Further properties

- [[Specific heat of an ideal gas]]
- [[Entropy of an ideal gas]]

## Types of ideal gas
Ideal gases come in three types #to/inquire

1. **Monoatomic** $\alpha = 3 /2$
   — all its energy is translational since there are no axes of rotation,
   so we can calculate the [[Total energy in an ideal monoatomic gas]].
   In general, only [[Noble gases]] take this form,
   e.g. $\ce{He}$, $\ce{Ne}$.
2. **Diatomic** $\alpha = 5 / 2$
   — have rotational kinetic energy in one axis.
   Pure gases tend to take this form,
   e.g. $\ce{H2}$, $\ce{O2}$, $\ce{S2}$.
3. **Polyatomic**
   — have multiple axes of rotation,
   e.g. $\ce{H2O}$.

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#state/tidy | #SemBr