Unformatted text preview: the reaction since liquids and solids have a much smaller molar volume than gases and do not contribute in a significant manner to Δ(PV). c) If X is state function of Y and Z, then, dX = (∂X/∂Y)Z dZ + (∂X/∂Z)Y dY This equation is incorrect. The correct equation is given by: dX = (∂X/∂Y)Z dY + (∂X/∂Z)Y dZ Note how the units are consistent on the left and right hand sides of the equation since the units of Y cancel out and the units of Z cancel out. This is not the case in general in the equation given as choice c. d) Consider two ideal gases A and B at the same temperature, the rms speeds of their molecules Crms(A) and Crms(B) and their molar masses, MA and MB. If MA / MB = 4, then, Crms(A) / Crms(B) = ½. Look at solution to Question 3 Part b and you will note that the root mean squared speed of molecules in an ideal gas, as given by the 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 23.5 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 = (23.5 J/K.mol) / (32 g/mol) = 0.73 J/K.g = 0.73 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 8.161 mg/L at the temperature of 27.85 C and at the pressure of 0.100 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 densit...
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 Spring '07
 AREsker
 Physical chemistry, Thermodynamics, pH

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