Intermolecular Forces and States of Matter

What are intermolecular forces?

Attractions between molecules that hold them together, originating from the mutual attraction of unlike charges or the mutual repulsion of like charges.

What properties differentiate the phases of matter?

Density, molar volume, molecular shape, and strength of intermolecular forces.

What causes dispersion (London) forces?

Fluctuations of electron distribution within molecules and atoms.

How do the shape and sizes of molecules affect dispersion forces?

They affect the magnitude of dispersion forces and macroscopic physical properties like boiling point.

What are polar molecules and how do they interact?

Polar molecules have permanent dipoles that attract each other through dipole-dipole interactions.

What is hydrogen bonding?

A strong type of dipole-dipole interaction that occurs between molecules with hydrogen bonded to highly electronegative atoms.

How can you rank molecular compounds with respect to boiling point?

By considering the strength of intermolecular forces present in the compounds.

What is surface tension and what causes it?

Surface tension is the resistance of a liquid's surface to an external force, caused by intermolecular forces.

What factors contribute to viscosity?

Intermolecular forces, mass, shape, and length of molecules.

What is capillary action?

The ability of a liquid to flow in narrow spaces without the assistance of external forces, resulting from cohesive and adhesive forces.

What is the heat of vaporization (ΔHvap)?

A quantitative measure for the process of vaporization.

How does vapor pressure depend on temperature?

Vapor pressure increases with temperature.

What is the Clausius-Clapeyron equation used for?

To relate temperature and vapor pressure.

Define critical temperature and critical pressure.

Critical temperature is the temperature above which a substance cannot exist as a liquid, and critical pressure is the pressure required to liquefy a gas at its critical temperature.

What is sublimation?

The transition of a substance from solid to gas without passing through the liquid phase.

What is fusion in the context of phase changes?

The process of melting, where a solid turns into a liquid.

What is a phase diagram?

A graphical representation that shows the states of matter for a substance as a function of temperature and pressure.

What is the difference between polar and nonpolar covalent bonds?

Polar covalent bonds involve unequal sharing of electrons, while nonpolar covalent bonds involve equal sharing.

What is a dipole moment?

A measure of the separation of positive and negative charges in a molecule.

What is the Debye unit?

A unit of measure for net dipole moments.

How do individual bond polarities affect molecular polarity?

If the individual bond polarities do not cancel, the molecule has a net dipole moment and is polar; if they do cancel, the molecule is nonpolar.

What is the electrical force in chemical bonds?

The electrical forces that hold two atoms together in a molecule or ionic compound.

What is electronegativity?

The relative ability of an atom to attract electrons in a bond to itself.

What are Ion-Dipole Forces?

The result of electrical interactions between an ion and the partial charges on a polar molecule.

What are London Dispersion Forces?

The result of motion of electrons which gives the molecule a short-lived dipole moment that induces temporary dipoles in neighboring molecules.

How do London Dispersion Forces affect boiling points?

As dispersion forces increase, the intermolecular forces increase, leading to higher boiling points.

What is the relationship between molecular size and London Dispersion Forces?

As the size of the molecule increases, the dispersion forces increase.

What is the significance of branched vs. straight-chain isomers in boiling points?

Branched chains have lower boiling points than straight chains due to less surface-to-surface contact.

What are Dipole-Dipole Forces?

The result of electrical interactions between dipoles on neighboring molecules.

How do Dipole-Dipole Forces influence boiling points?

As dipole forces increase, the intermolecular forces increase, resulting in higher boiling points.

What defines Hydrogen Bonding?

An attractive force between a hydrogen atom bonded to a very electronegative atom (O, N, or F) and an unshared electron pair on another electronegative atom.

How does hydrogen bonding affect the density of water?

The density of water decreases as it freezes due to hydrogen bonding resulting in a cage-like structure in the solid state.

What role does hydrogen bonding play in DNA?

Hydrogen bonding occurs between complementary sites on double-stranded DNA.

What factors affect surface tension in liquids?

Surface tension is affected by molecular shape (polarity), molar mass, and temperature.

What is viscosity?

Viscosity is a measure of resistance to the flow of a fluid.

What factors influence viscosity?

Viscosity is influenced by molecular shape (polarity), molar mass, and temperature.

What are cohesive and adhesive forces?

Cohesive forces are interactions between like particles, while adhesive forces are interactions between unlike particles.

What is the effect of cohesive forces on meniscus shape?

A convex meniscus occurs when cohesive forces are greater than adhesive forces; a concave meniscus occurs when adhesive forces are greater than or equal to cohesive forces.

Which substance is likely to have the highest viscosity at 25°C: C4H10, HOCH2CH2OH, C8H18, or C2H5NH2?

HOCH2CH2OH is likely to have the highest viscosity due to hydrogen bonding.

Which substance is expected to have the highest surface tension at 25°C: C5H12, C6H6, C2H5OH, or C3H5(OH)3?

C3H5(OH)3 is expected to have the highest surface tension due to multiple hydroxyl groups.

What is the relationship between vaporization and surface area?

The larger the surface area, the faster the rate of evaporation due to high-energy molecules at the surface overcoming attractive forces.

How do intermolecular forces relate to boiling points of binary hydrides?

Increased boiling points are related to stronger attractive forces, such as hydrogen bonding.

What type of intermolecular force is dominant in CO2, SO2, CCl4, CH4, and HNO3?

CO2 has dispersion forces; SO2 has dipole-dipole forces; CCl4 has dispersion forces; CH4 has dispersion forces; HNO3 has hydrogen bonding.

What is the effect of dipole-dipole attraction on boiling and melting points?

Dipole-dipole attractions generally increase boiling and melting points due to stronger intermolecular forces.

What is the significance of the sphere of hydration in ion-dipole interactions?

The sphere of hydration refers to the arrangement of water molecules around an ion, enhancing ion-dipole interactions.

What is vapor pressure?

The pressure exerted by a gas in equilibrium with its liquid, where rates of evaporation and condensation are equal.

What is the normal boiling point?

The boiling point of a liquid when the external pressure is at standard pressure (1 atm).

What factors affect vapor pressure?

Temperature (directly proportional) and intermolecular forces (inversely proportional). Stronger intermolecular forces require higher energy to enter the gas phase.

How does the presence of a nonvolatile solute affect vapor pressure?

It decreases the vapor pressure of a solution compared to that of the pure solvent.

What happens to the fraction of molecules with escape energy as temperature increases?

The fraction increases, leading to a faster rate of evaporation.

What is the relationship between vaporization and temperature?

As temperature increases, the rate of evaporation increases.

What is vaporization in terms of energy?

Vaporization is an endothermic process that requires energy input to overcome molecular attractions.

What is the relationship between ΔHcondensation and ΔHvaporization?

ΔHcondensation = -ΔHvaporization.

What is the effect of attractive forces on vapor pressure?

Weaker attractive forces result in higher vapor pressure and greater volatility of the liquid.

How does temperature affect vapor pressure?

Increasing temperature increases the number of molecules able to escape the liquid, thus increasing vapor pressure.

What is the Clausius-Clapeyron equation?

lnPvap = lnβ - ΔHvap/RT, where lnPvap is the natural logarithm of vapor pressure and R is the gas constant.

What does the slope of the Clausius-Clapeyron plot represent?

The slope represents -ΔHvap / R.

What is the significance of the vapor pressure at the normal boiling point?

At the normal boiling point, the vapor pressure equals 760 torr, or 1 atm.

What happens to the temperature of a liquid at its boiling point when heat is added?

The temperature remains constant while all added heat goes into boiling the liquid.

What is the formula for calculating heat during the heating of a liquid?

q = mass × Cs × ΔT, where Cs is the specific heat capacity.

What is the enthalpy of vaporization if the slope of the graph is -2996 K?

The enthalpy of vaporization can be calculated using the slope in the Clausius-Clapeyron equation.

How can the vapor pressure be predicted using the Clausius-Clapeyron equation?

By using two measurements of vapor pressure and temperature or knowing the heat of vaporization and the normal boiling point.

What is the process when high-energy molecules are lost from a liquid?

The average kinetic energy of the remaining liquid decreases, leading to a temperature drop.

What is the effect of external pressure on the boiling point of a liquid?

The lower the external pressure, the lower the boiling point of the liquid.

How much energy is required to vaporize 2.58 kg of water at its boiling point?

This requires a calculation based on the heat of vaporization.

How many grams of isopropyl alcohol will require 21.8 kJ of energy to vaporize?

This requires a calculation based on its ΔHvap of 39.9 kJ/mol.

What happens to the temperature of a solid as it is heated until it reaches the melting point?

The temperature increases linearly until it reaches the melting point.

What is the formula to calculate the heat (q) required to raise the temperature of a solid?

q = mass × Cs × ΔT, where Cs is the specific heat capacity and ΔT is the change in temperature.

What occurs to the temperature of a solid at its melting point when heat is added?

The temperature remains constant as all added heat goes into melting the solid.

What is the temperature of ice/water at 1 atm pressure?

0 °C.

What is the nature of melting in terms of energy?

Melting is an endothermic process, requiring energy input to overcome molecular attractions.

What is the heat of fusion (ΔHfus)?

The amount of heat energy required to melt one mole of a solid; it is positive and somewhat temperature dependent.

What is the relationship between ΔHcrystallization and ΔHfusion?

ΔHcrystallization = -ΔHfusion.

How does sublimation occur?

Molecules in the solid state gain enough thermal energy to break free from the surface and become a gas.

What is deposition in the context of phase changes?

The process of capturing vapor molecules into a solid.

What is the significance of the triple point in a phase diagram?

It is the point at which three phases coexist in equilibrium.

What is the critical point in a phase diagram?

A combination of temperature and pressure beyond which a gas cannot be liquefied.

What is a supercritical fluid?

A state of matter beyond the critical point that is neither liquid nor gas.

What is the specific heat capacity of ice (cice)?

2.09 J/g °C.

What is the specific heat capacity of liquid water (cliquid)?

4.18 J/g °C.

What is the specific heat capacity of water vapor (cgas)?

2.01 J/g °C.

What is the total heat (qtotal) required to heat 1.0 mole of water through its heating curve?

56.1 kJ/mol.

What is the ΔHfusion for ice?

6.02 kJ/mol.

In a phase diagram, what does a negative slope of the solid-liquid line indicate for water?

It indicates that ice is less dense than liquid water.

What happens to CO2 at a pressure of 2 atm when the temperature is increased from -100°C to 0°C?

The CO2 will undergo phase changes depending on its position in the phase diagram.

At 10 atm pressure, which phase of gallium is more dense, solid or liquid?

The phase that is more dense can be determined from the phase diagram.

What is the effect of reducing pressure from 72 atm to 5.0 atm at -30°C on CO2?

The CO2 will undergo phase changes as indicated in the phase diagram.

What is the significance of the heating curve of a solid?

It illustrates the relationship between temperature and phase changes as heat is added.