Question

Question

1. Describe four types of intermolecular interactions; sketch attractions between molecules (somehow communicate what the attraction is). Which of these is the strongest? Which is the weakest? What can a substance’s phase at room temperature tell us about the intermolecular interactions?

2. What types of substances can hydrogen bond? What is special about the hydrogen bond?

3. Define each of the following: vaporization; condensation; sublimation; deposition; melting (fusion); freezing. Which of these are exothermic? Which are endothermic?

4. Define the “heat of fusion” (ΔH_fus) and “heat of vaporization” (ΔH_vap). Why do these processes require an input of energy? What is the energy used for?

Answer 1

There are four types of intermolecular forces

Ionic interactions are interactions between charged atoms or molecules Ex :NaCl

Hydrogen bonding occurs in molecules having highly electronegative elements F, O, or N directly bound to hydrogen

Vander wal interactions takes place due to strong elctronnege atoms. The more electronegative atom receives partial -ve charge and the electropositive elements receives partial positive charge. The bond between Carbon and oxygen is an example of Vander wal interactions

London forces are interaction between instantaneosu dipoles in a molecule.

b) Hydrogen bonding occurs between highly electronegative elements and hydrogen. These bonds will have significant bond strenghts which make their boilng points higher.

c) Vaporozation refers to phase transition from liquid to Vapor. Vaorization takes place from the surface

Condensation :Change of phase transition from vapor to liquid

Sublimation is a unit operation where a solid directly passes the vapor phase without becoming liquid

depositionThe direct solidification of a vapor by cooling;

Melting is a physical change where a solid becomes a liquid

Freezing is a unit operation where a liquid becoms a solid

Exothermic : freezing, deposition, condensation.

Endothermic : melting, sublimation, vaporization

4. Heat of fusion is the amoumt of heat required to convert a solid to liquid at constant temperature. Heat of vaporization is the amount of heat required to convert a liqudi at constant temperature to vapir.

They need heat energy. Because the molecualr distance is more in liquid and vapor compared to solid and liquid respectively.