12.07.2015 Views

Theoretical Test

Theoretical Test

Theoretical Test

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1. Avogadro's number (5pts)Spherical water droplets are dispersed in argon gas. At 27 o C, each droplet is1.0 micrometer in diameter and undergoes collisions with argon. Assume thatinter-droplet collisions do not occur. The root-mean-square speed of thesedroplets was determined to be 0.50 cm/s at 27 o C. The density of a water dropletis 1.0 g/cm 3 .1-1. Calculate the average kinetic energy (mv 2 /2) of this droplet at 27 o C. Thevolume of a sphere is given by (4/3) π r 3 where r is the radius.If the temperature is changed, then droplet size and speed of the droplet willalso change. The average kinetic energy of a droplet between 0 o C and 100 o Cas a function of temperature is found to be linear. Assume that it remains linearbelow 0 o C.0At thermal equlibrium, the average kinetic energy is the same irrespective ofparticle masses (equipartition theorem).The specific heat capacity, at constant volume, of argon (atomic weight, 40)gas is 0.31 J g -1 K -1 .1-2. Calculate Avogadro's number without using the ideal gas law, the gasconstant, Boltzmann’s constant).1

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