Page 368 - Physics Coursebook 2015 (A level)

Cambridge International A Level Physics
Summary
■■ Brownian motion provides evidence for the fast, random movement of molecules in a gas.
■■ From the kinetic model of a gas, we can deduce the relationship:
p = 13 Nm< c 2> = 13 ρ < c 2> V
where <c2> is the mean square molecular speed and ρ is the density of the gas.
■■ The mean translational kinetic energy E of a particle (atom or molecule) of an ideal gas is proportional to the thermodynamic temperature T.
E = 12 m <c2> = 3kT 2
■■ For an ideal gas: pV = constant
T
■■ One mole of any substance contains NA particles
(atoms or molecules).
NA = Avogadro constant = 6.02 × 1023 mol−1 ■■ The equation of state for an ideal gas is:
pV=nRT fornmoles
End-of-chapter questions
1 a
State how many atoms there are in:
i a mole of helium gas [1]
ii a mole of chlorine gas [1]
iii a kilomole of neon gas. [1]
b A container holds four moles of carbon dioxide. Calculate:
i the number of carbon dioxide molecules there are in the container [1]
ii the number of carbon atoms there are in the container [1]
iii the number of oxygen atoms there are in the container. [1]
2 A bar of gold has a mass of 1.0 kg. Calculate:
a the number of moles of gold in the bar [2]
b the number of gold atoms in the bar [1]
c the mass of one gold atom. [1]
(Relative atomic mass of gold = 197.)
3 A cylinder holds 140 dm3 of nitrogen at room temperature and pressure. Moving slowly so that there is no change in temperature, a piston is pushed to reduce the volume of the nitrogen to 42 dm3.
a Calculate the pressure of the nitrogen after compression. [2]
b Explain the effect on the temperature and pressure of the nitrogen if the piston were pushed in
very quickly. [1]
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