A-Level Physics OCR A H556

amount of substance in moles; Avogadro constant N_A equals 6.02 × 10²³ mol^–1

model of kinetic theory of gases

*Assumptions for the model:

• large number of molecules in random, rapid motion
• particles (atoms or molecules) occupy negligible volume compared to the volume of gas
• all collisions are perfectly elastic and the time of the collisions is negligible compared to the time between collisions
• negligible forces between particles except during collision*

pressure in terms of this model

(i) the equation of state of an ideal gas $pV = nRT$, where n is the number of moles

(ii) techniques and procedures used to investigate $PV = \text{constant}$ (Boyle’s law) and $\dfrac{P}{T} = \text{constant}$

PAG8

(iii) an estimation of absolute zero using variation of gas temperature with pressure

PAG8

the equation $pV = \dfrac{1}{3} Nm\bar{c}^2$,

where N is the number of particles (atoms or molecules) and $\bar{c}^2$ is the mean square speed

Derivation of this equation is not required.

root mean square (r.m.s.) speed; mean square speed

Learners should know about the general characteristics of the Maxwell-Boltzmann distribution.

the Boltzmann constant; $k = \dfrac{R}{N_A}$

$pV = NkT$; $\dfrac{1}{2}m\bar{c}^2= \dfrac{3}{2}kT$

Learners will also be expected to know the derivation of the equation $\dfrac{1}{2}m\bar{c}^2= \dfrac{3}{2}kT$ from $pV = \dfrac{1}{3} Nm\bar{c}^2$ and $pV = NkT$

internal energy of an ideal gas.