Question

True or fase:
a. heats of vaporization are greater than heats of fusion
b. under ordinary conditions, a substance will sublime rather than melt if it's triple point occurs at a pressure above atmospheric pressure
c. the type of solid that is characterized by low melting point, softness, and low electrical conduction is a covalent network solid
d. inside a unit cell, spheres on the edges are shared by 8 unit cells and are counted as 1/8 in the cell

Answer 1

a)True

Heat of fusion of water =333.55 J/g

Heat of vaporization of water =2257J/g

b) True

Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase.Sublimation is an endothermic phase transition that occurs at temperatures and pressures below a substance's triple point in its phase diagram. In other words under ordinary conditions, a substance will sublime rather than melt if it's triple point occurs at a pressure above atmospheric pressure

c) False

Network covalent solids are characterized by high Melting Point and Hardness Eg Diamond,Quartz

Molecular solids are characterized by low Melting Point, Softness and low electrical conductivity Eg CO2(s)

d) False

inside a unit cell, spheres on the corners are shared by 8 unit cells and are counted as 1/8 in the cell

inside a unit cell, spheres on the edges are shared by 4 unit cells and are counted as 1/4 in the cell