Evaporation occurs as a result of molecules originally in the liquid state acqui

Question

Evaporation occurs as a result of molecules originally in the liquid state acquiring enough kinetic energy to escape from the surface of the liquid to the gaseous state Molecules have inter- molecular attractions with other molecules Wore of these attractive forces are present in the liquid state than in the gaseous state To go from the liquid state to the gaseous state, molecules must become free of these sometimes strong inter-molecular forces. The molecules that gain the energy to break these attractive forces are the ones that begin to leave the surface, i e. evaporation starts to take place The rate of evaporation then is decided by the number and types of intermolecular forces present between molecules Compound A has greater number of the same type of intermolecular forces than compound B possesses. Both compounds have almost the same molar mass. Which compound will evaporate faster? Why? Examples of inter-molecular forces are dispersion forces, dipole-dipole forces and hydrogen-bonding. Among these, hydrogen bonding contains the most energy (5-30 KJ/mol) which is only 20 times weaker than a typical covalent bond. Hydrogen bonding is found in molecule that contain O-H, N-H and H-F bonds. Dipole-dipole forces are present in molecules that contain polar bonds (X-Y where both atoms are of different electronegativity), Dispersion forces are present between any two atoms in all molecules. Compound C has hydrogen bonding between molecules but compound D does not The molar mass of both are similar. Which will evaporate faster? Why?

Explanation / Answer

Q1.

if A has greater number of the SAME intermolecular force

then, by definition, we need to break MORE numebr of interactions

meaning we require MORE energy for A, therefore

we require much more time/energy for A, the faster will be then B

Q2.

Hydrogne bondings require energy to be broken down and let the molecules to evaporate

than

if C contains H-bonds, then the energy requirement must be higher for C

that is,

the compound D will evaporate faster

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