Question

Phase changes always associate with change of enthalpy. For the following situations, name the phase transition and indicate whether the process is exothermic or endothermic.

. Dry ice (solid carbon dioxide) turns to gaseous carbon dioxide. Answer:

. Water vapor turns to liquid water. Answer:

. Solid iron turns to liquid iron. Answer:

. Iodine vapor turns to solid iodine. Answer:

. Liquid helium turns to helium gas. Answer:

True or false

. Intermolecular forces are stronger than ionic and covalent bonds. Answer:

. For molecules with similar size and molar mass, those with higher polarity would have higher boiling point. Answer:

. Ion-dipole forces exist between ionic potassium bromide and polar water. Answer:

. Dispersion forces exist between argon and helium. Answer:

. Instantaneous dipoles exist in all molecules and atoms. Answer:

. The strength of dispersion forces depends on the molar mass but the shape of the molecules have no effect on dispersion forces. Answer:

. Ice has a higher density than water because ice has an ordered cagelike structure. Answer:

. Liquids with weaker intermolecular interactions have lower viscosity. Answer:

. Viscosity decreases with increasing temperature. Answer:

. For any molecules, the heat of vaporization is always lower than the heat of fusion because it takes more energy to make molecules to move past one another in a solid lattice. Answer:

Answer 1

Dry ice (solid carbon dioxide) turns to gaseous carbon dioxide.

Answer:conversion of solid to gas is called sublimation. enthalphy of sublimation requires heat to be obsorbed by solid to get converted in to gas, hence, enthaply change is Positive

Water vapor turns to liquid water.

Answer: vapour to liquid is called condensation

we know that heat is needed to evapourate water we must give heat to water. it is reverse process hence heat will be released. hence, enthalpy change is Negative

Solid iron turns to liquid iron.

Answer: it is call melting

it requires heat. enthalpy change is Positive

Iodine vapor turns to solid iodine. Answer: process is deposition: it releases heat, hence, enthalpy is Negative

Liquid helium turns to helium gas. Answer:True : it canl be converted into gas

Intermolecular forces are stronger than ionic and covalent bonds. Answer: no