Question

1. Why is the boiling point of NaCl higher than that of C3H8?

a. ion-ion interactions are stronger than induced-dipole interactions.

b. dipole-dipole interactions are stronger than ion-ion interactions.

c. induced dipoles can be generated in C3H8.

d. hydrogen bonds cannot form in NaCl.

e. covalent bonding in bonding in C3H8 is weak.

Increasing volume of a gaseous sample, while holding the number of moles within constant, decreases pressure. Why is this?

a. Particles become less dense and exert less pressure

b. Particle on average collide less frequently with the walls of the container

c. As V is raised the walls of the container swell – resulting in decreased pressure

d. At higher V particles collide more frequently and with more force with the walls of the container

e. The heat capacities of gas changes as T is increased leading to decreased Pressure

Answer 1

1) NaCl is ionic compound, it has ion-ion interactions which are very strong due to electrostatic interaction, whereas C3H8 is covalent and it shows induced dipole interactions which are very weak.

ion-ion interactions >> induced dipole interaction

Hence NaCl need more energy to break its intermolecular interactions compared to C3H8. Therefore NaCl has greater melting point.

Answer: a. ion-ion interactions are stronger than induced-dipole interactions.

2) When volume of the gas increase keeping the number of moles same, no. of molecules per unit volume decreases. As a result less no. of gas molecules collide with container wall.

Since pressure no. of collitions per unit area, pressure of the gas decreases.

Answer: b. Particle on average collide less frequently with the walls of the container