Question

I. Methanol $\left( {{\text{C}}{{\text{H}}_3}{\text{OH}}} \right)$ has a lower boiling point than that of propane $\left( {{{\text{C}}_3}{{\text{H}}_8}} \right)$
II. Molecules of higher molecular weight have lower kinetic energy than lower molecular weight molecules when the different substances are at the same temperature.
A.Statement I is true, Statement II is true
B.Statement I is true, Statement II is false
C.Statement I is false, Statement II is true
D.Statement I is false, Statement II is false

Answer 1

The greater the intermolecular forces of attraction the higher the melting point or boiling points. The kinetic energy is a function of temperature and not the molecular weight of molecules.

Complete step by step answer:
Methanol is an alcohol whereas propane is an unsaturated hydrocarbon that is the hydrocarbon containing only sigma bonds. Hydrogen bonds are present in alcohol because of hydrogen attached with electronegative atom search of oxygen. There is no such hydrogen bonding present in propane, because of the absence of any suitable element. Here, only Van der waal forces of attraction are there. So, due to the presence of strong hydrogen bonds, methanol has a higher boiling point than propane. So the statement one is false.
The kinetic energy for a molecule is a function of temperature and not of the molecular weight of the molecule. Hence two molecules at same temperature will have the same total kinetic energy irrespective of the molecular weight. So the kinetic energy of alcohol and propane will be the same. Hence the statement 2 is also false.

The Correct option is D.

Note:
Boiling point is the point at which liquid and vapour exist in equilibrium with each other. The boiling occurs when the vapour pressure becomes equal to the atmospheric pressure. The higher the external pressure higher heat will be required to make a vapour pressure equal to the atmospheric pressure and hence higher will be the boiling point. The boiling point of methanol is $64.7^\circ {\text{C}}$. The boiling point of propane is $- 42^\circ {\text{C}}$.