AP Chemistry Question of the Day --32

Welcome back to my blog. Here comes the answer to question 31 I posted yesterday. The correct answer is E.

When pressure is high and temperature is low, we can consider gases as ideal gas and they obey the ideal gas law. The molar volume of any gas would be the same at the same pressure and temperature according to PV=nRT, the molar volume (n=1)would be: V(molar)=RT/P. Under ideal gas conditions, the volume and the intermolecular interactions between gas molecules are negligible. However, when temperature is low and the pressure is high, especially when the gas is close to condense, both the volume and the intermolecular forces have to be taken into account. The stronger the intermolecular force, the less the volume. Both C2H6  and H2 are non polar molecules. Since C2H6 has higher molecular weight and more complicated electronic structure, it has stronger London Dispersion forces than H2. So E is the right answer.

Answer A is incorrect because C2H6 is larger than H2. The average kinetic energy is only dependent on the temperature. At the same temperature,  both gases have the same average kinetic energy. Thus, B and C are wrong. 



Following is Question 32 of the series. 

32. In which compound does manganese have the lowest oxidation state? 

A MnO2 
B MnI2 
C K2MnO4 
D Mn2O7 
E KMnO4 

I will post the answer and explanation tomorrow. 

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