Question

23. Which set of gases is listed from lowest to highest root-mean-square speed at 25°C? a. Kr< CO2 <NO2 < SF d. SF6 <Kr<NO2 <CO2 b. SF6 <NO, <CO2 <Kr e. CO2 <NO, <Kr <SF c. SF6<Kr <CO2 <NO2 24. Which set of gases is listed from fastest to slowest effusion rate? a. N2O > NO2 > NO > N204 d. NO > NO2 >N,O > N204 b. NO > N20 > NO2 > N204 e. N204 > N20 > NO2 > NO c. N204 > NO2 > N20 > NO 25. The van der Waals equation for real gases contains an a parameter and a b parameter. Which statement about these parameters is not correct? a. One of these parameters accounts for the fact that the molecules occupy space and thereby reduce the free volume of the container b. One of these parameters accounts for the fact that attractive forces between the molecules serve to reduce the pressure exerted on the walls of the container. c. The van der Waals equation is defined so both of these parameters have negative values d. Both of these parameters increase with increasing number of atoms in each molecule. e. Both of these parameters increase with increasing mass of the molecules.

Answer 1

The root mean square speed of a gas Crms = Sqrt(3RT/M) that means RMS speed is inversely proportional to square root of its molecular weight. The order of molecular weight is

SF6 > Kr > NO2 > CO2. The order of root mean square speed is SF6 < Kr< NO2<CO2.

2. They rate of effusion is inversely proportional to square root of its molecular weight. The order of molecular weight is NO<N2O<NO2<N2O4.

They order of effusion rate is NO>N2O>NO2>N2O4.

25. Both the parameters a, b increases with the increase in mass of molecules is incorrect. It is independent of mass of molecules.