Unformatted text preview: of partial pressures PA/PB is equal to the ratio of the mole fractions xA/xB This is correct and a result of Dalton’s law. The partial pressure of a component A in an ideal gas mixture is given as PA = xAP where xA is the mole fraction of A in the mixture and P is the total pressure. Hence, applying this equation to two components A and B of a mixture leads to PA/PB = xAP/xBP = xA/xB b) The relationship between ΔH and ΔU for a chemical reaction occurring at constant T is given by:
ΔU = ΔH + RT Δng This is incorrect. The correct relationship is the direct result of H = U + PV applied to the products and the reactants in a gas reaction. ΔH = ΔU + Δ(PV). The difference Δ(PV) for a chemical reaction occurring at constant temperature T isequal to Δ(ngasRT) = RT Δ(ngas). Note that we are only 3 considering the gas species in 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). Hence, the sign is wrong: Should be… ΔU = ΔH  RT Δng c) If X is state function of Y and Z, then, dX = (∂X/∂Y)Z dY + (∂X/∂Z)Y dZ This is correct. Look at the units (Left hand side and right hand side units are these of X) 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...
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 Spring '07
 AREsker
 Physical chemistry, Thermodynamics, pH

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