Unformatted text preview: kinetic theory of gases suggests that C is directly proportional to the square root of the absolute temperature and inversely proportional to the square root of the molar mass. Hence, if the molar mass increases by a factor of 4 (at constant temperature), then, the speed must decrease by a factor of 2. Question 8: (5 points) A substance has a molar heat capacity equal to 29.5 J/K.mol, a molar mass equal to 32 g/mol and a 3
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density of 1.54 mg/cm . Calculate the specific heat capacity of the substance in J/g. C. The specific heat capacity is the heat capacity per unit mass. Hence, to obtain
the specific heat capacity, you must divide the molar heat capacity by the molar mass. o
Cs = (29.5 J/K.mol) / (32 g/mol) = 0.92 J/K.g = 0.92 J/ C.g Please, note that heat capacities are defined as heat (q) or thermal energy (ΔU) per unit of temperature change (ΔT). A change in temperature can be expressed with the same magnitude in o
kelvin or in degree Celsius. Hence, 1 J/K.g = 1 J/ C.g. Question 9: (11 points) o
An ideal gas has a density of 0.8161 mg/L at the temperature of 27.85 C and at the pressure of 0.0100 atm. Determine the molar mass of this gas (10 points) and indicate what that gaseous substance might be (1 point). Here, we use the ideal gas law PV = nRT and combine this law with the definition of density ρ = m / V and the definition of molar mass, M = m / n. This leads to : PM = ρ RT or M = ρ RT / P Using SI units we get: M = ρ RT / P 6
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M = (0.8161 mg/L) x (1 kg/10 mg) x (1000 L/m ) x 8.3145 J/K.mol x (273.15 + 27.85 K) / (0....
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 Spring '07
 AREsker
 Physical chemistry, Thermodynamics, pH

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