Page 6 of 11 In a closed chamber an Ultra High Vacuum has been achieved where th
ID: 1877953 • Letter: P
Question
Page 6 of 11 In a closed chamber an Ultra High Vacuum has been achieved where the gas pressure inside is as low as 1.0 10*Pa At a temperature of 21 C, how many there in I em 2.5 10 molecules b. 2.510 molecules 3.4 10 molecules d. 3.4 10" molecules 3.4 10" molecules 5. Three 25-g ice cubes are dropped into 350 g of water in a glass. If the water is initially at temperature of the drink a temperature of 28 C and the ice at -12 C, what is the final Ignore any heat exchange between the glass cup and the water inside. 79.7 cal/s a. 22"C b. 20 C c.96°C d. 9.0C 7.9°C 6. Assume that a 1.0-inch thick wall made of solid wood is to be replaced by a concrete wall that has the same surface area. How thick should the concrete wall be in order to have the same rate of heat flow through it? The thermal conductivity, of concrete is 0.34 's m C" and the thermal conductivity of wood is 0.10 1/s m C a 0.12 in b 3.3 in 84 in d 12in 21 inExplanation / Answer
4.
Using ideal gas law:
PV = nRT
n = PV/RT
Using given values
P = 1.0*10^-8 Pa
V = 1.0 cm^3
T = 21 C
R = gas constant
So,
n = (1.0*10^-8 Pa)*(1 cm^3)/((273 + 21)*(8.314*10^6 cm^3-Pa/(K-mol)))
n = 10^-8/(294*8.314*10^6)
n = 4.09*10^-18 moles
No. of molecules = n*Na = 4.09*10^-18*6.023*10^23
No. of molecules = 2.46*10^6 molecules = 2.5*10^6 molecules
Correct option is A.
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