Name: General Chemistry II, Fall 2018 Test #2 (3 pts) What kind of molecules hav

Question

Name: General Chemistry II, Fall 2018 Test #2 (3 pts) What kind of molecules have London dispe only polar molecules only nonpolar molecules only molecules with H bound to F.O, or N all molecules a. b, d) 2. 3 pts) Why are London dispersion forces so weak? because both molecules have outer electrons that rav a diole repel each other b. because they occur only in molecules that do not hav c. because the dipoles present in the d. are none of these reasons are correct. reasons are correch molecules are very short-lived. charges. How does a nonpolar 9 pts) London dispersion forces involve the attractions of + molecule like O: (O) get + and - charges? spersion forces involve the attractions of + and - . (15 pts) The strongest IMF that liquid hydrogen peroxide (H.O,) has is hydrogen bonding forces and the strongest IMF that liquid hydrogen sulfide (H,S) has is London dispersion forces liquid will have a higher vapor pressure? Explain why this happens. (15 pts) Explain how the evaporation rate of the same liquid will change if you cool it from 75 °C to 50 °C. Why does this happen?

Explanation / Answer

1)LONDON DISPERSION FORCES are present between any two molecules.It is predominant in non-polar molecules,however,it is present in polar molecules too when they are almost touching.

So,the correct answer is (d)

2)

The London dispersion force is the weakest intermolecular force. The London dispersion force is a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles. Because of the constant motion of the electrons, an atom or molecule can develop a temporary (instantaneous) dipole when its electrons are distributed unsymmetrically about the nucleus.

So,correct answer is (C)

3)Temporary dipoles (Van Der Waal) forces are caused by the electrons in a oxygen molecule continuously moving from one end of the specie to the other, creating areas of unequal distribution of electrons i.e.one side of the molecule acquires positive charge where there are fewer electrons, and other side attains negative charge, where there are more electrons. Now this molecule induces dipoles in neighbouring molecules and this results electrostatic attractions between oppositely charged temporary dipole.

4)

Vapor pressure is the amount of gas in equilibrium with the liquid and solid phases. The higher the vapor pressure, the more gas in equilibrium, and thus the easier it is for the substance to vaporize (turn to gas), and vice versa.

Intermolecular forces are the attractive interactions between molecules. For something to vaporize, we need to give enough energy together to break these interactions. As a result, we'll need more energy (due to higher temperature) to break apart stronger intermolecular forces.

Since higher vapor pressures corresponds to more gas in equilibrium, the intermolecular forces are therefore primarily weaker for higher vapor pressures.

So,H2S will have higher vapor pressure as compared to H2O2.

5)Temperature is directly proportional to the rate of evaporation. It is so because, when we increase the temp of our heating source, we supply more energy to the liquid to be evaporated. This energy is stored in the form of kinetic energy in the molecules.

With the increase in temperature, the molecules tend to collide with each other and begin to move faster until some of the molecules escape into the atmosphere. And so evaporation takes place.

So, the liquid which is heated at 75 degree celcius will have higher evaporation rate as compared to that of 50 degree celcius.

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