Intro to Chem: Exam 3 Review

Hydrogen Bonding Force

- *hydrogen to O, N, or F* > strong dipole-dipole force between polar molecules that contain hydrogen attached to a highly electronegative element - occurs in specific directions pointing at unshared electron pair on highly electronegative atom on adjacent molecule

Network Solids

- atoms > covalent bonds > very high melting points, very hard, somewhat brittle, nondonductors/semiconductors - form carbon in form of diamond/graphite

Ionic Crystalline Solid

- cations and anions - high melting point, hard, brittle, nonconductors when solid, malleable and ductile > holes within structure

Dipole-Dipole Forces

- partially negative end of one polar molecule and partially positive end of another polar molecule - MUST BE POLAR - attractions between polar molecules are stronger than those between nonpolar molecules of similar size

Molecular Crystalline Solids

- polar/nonpolar molecules - dipole-dipole forces/london dispersion - FOR POLAR: low-to-moderate melting point, variable hardness, maybe brittle, nonconductors - FOR NONPOLAR: low melting point, soft, poor heat conductors, electrical insulators, weak london dispersion > intermolecular forces between molecules hold a molecular solid together

London Dispersion Forces

- results from formation of temporary dipoles in molecules > found in ANY atom/molecule - temporary dipole in one molecule induces formation of a temporary dipole in nearby molecule and attracted to it - stronger with larger atom/molecule; size of electron cloud causes this- the larger the cloud; the easier to distort

What is the relation with surface tension and temperature?

- surface tension decreases as temperature increases

Explain relation to velocity

- the velocity is greater for the gas particles at higher temps - when comparing 2 gases of different molar masses at the same temp, particles w/ smaller mass have greater velocities and move faster

Explain Ideal Gas Law

- under the same temperature, pressure, volume all gases contain the same number of molecules (but not the same mass)

How does vapor pressure of liquid relate to intermolecular forces?

- vapor pressure decreases when intermolecular forces increase

How does vapor pressure of liquid relate to temperature?

- vapor pressure increases with temperature

Explain Viscosity relation:

- viscosity, resistance to flow, increases with intermolecular force strength and molecular size REMEMBER: THAT LOW VISCOSITY IS LIKE WATER; HIGH VISCOSITY IS LIKE HONEY

Surface Tension

- work needed to expand surface of liquid; the property of a liquid surface that causes it to behave like a stretched membrane - the greater the intermolecular forces in a liquid, the greater the surface tension

Comparing total intermolecular forces of substances:

1. Hydrogen bond strongest unless crazy difference in molar masses 2. When comparing polar/nonpolar substances, with diff molar masses, the one with greatest molar mass will have greatest intermolecular forces 3. If they have the same molar mass and they are both polar, the more polar substance has the strongest; or one with greatest boiling point

Explain some of the postulates of the kinetic-molecular theory:

1. gases are made of small/widely separated particles 2. particles behave independently of each other 3. each particle in a gas is in rapid, straight-line motion until it collides with another molecule or with its container 4. the pressure of a gas arises from the sum of the collisions of the particles with the walls of the container 5. the average kinetic energy of gas particles depends only on the absolute temperature

What are the properties of metallic crystalline solids

> atoms > nuclei and delocalized valence electrons - low melting point and soft OR - high melting point and hard - good heat and electrical conductors - malleable and ductile

How does vapor pressure of liquid relate to boiling point?

> liquid boils when vapor pressure equals pressure above liquid; this is the boiling point

What does each part of the ideal gas law mean?

> pressure: measured in atm > volume: liters > n: moles of gas > R: .0821 > T: temp in Kelvin

Evaporation and Condensation depend on:

> temperature and concentration of molecules available - the rate of condensation equals rate of evaporation; concentration of molecules in gaseous states becomes constant

A weather balloon is filled with helium gas gets larger as it ascends to high altitudes The expansion of the balloon is due to:

A decrease in the rate of collision of the air molecules on the outside walls of the balloon

Describe Boyle's Law

At constant temperature, the volume occupied by a fixed amount of a gas is inversely proportional to its pressure

Why can evaporation cool a house?

Evaporation is endothermic- the energy water needs to evaporate comes from surrounding air

This means that the gas with the most moles will have the greatest volume at STP.

Hydrogen has most moles per gram because smallest

Solid vs Liquid molecular representation difference:

In a liquid, molecules do not show a clear pattern

A 1.5-L container of He and a 1.5-L container of O2 are both at 22°C and 760 torr. Which of the following statements about these gas samples is true? Choose the best answer.

The average kinetic energy of the He​​ atoms and O2​​ molecules is the same.

Vapor Pressure is lowest for compounds with hydrogen bonding

The ones with weakest intermolecular force has highest vapor pressure has highest vapor pressure; nonpolar would have most - among nonpolar, the one with greatest electrons would have lower vapor pressure

When two substances has similar molar mass, the polar substance will have stronger intermolecular forces

The strength of london dispersion forces increases as molecular size or molar mass increases

Why do different liquids have different vapor pressures?

The vapor pressures of pure liquids depend on the strength of the intermolecular forces between the particles of the liquids.

What is the relation between pressure and volume?

The volume is inversely proportional to its pressure

What is the origin of intermolecular forces?

They arise from the interaction of + and - charges

What is the relation between warm gases and densities?

Warm gases have lower densities

What is the relation between density and gases stored under pressure?

When gases are stored under pressure, their densities increase

What happens when more gas is added to a container?

When more gas is added to a container that is allowed to expand, the volume increases due to the presence of more gas particles

What is the relation between temperature and volume?

When temperature increases, volume increases

When will it convert to liquid?

When the temperature falls enough that the pressure of the gas matches the vapor pressure of the liquid, gas starts to condense

Which has a stronger London Dispersion Forces? Ar or Xe?

Xenon is stronger because it has more electrons

What is an alloy?

a metal with one additional metallic/nonmetallic

What is kinetic-molecular theory of gases?

assumes that gas particles occupy no volume and that there are no intermolecular forces between them

Explain Gay-Lussac's Law of Combining Volumes

chemical reactions occurring at constant pressure and temperature, the volumes of gaseous reactants/products are in ratio of the small whole numbers

Explain Avagardo's Hypothesis

equal volumes of all gases contain equal numbers of particles

Explain Charles Law

for a given mass of a gas at constant pressure, volume is directly proportional to temperature on the kelvin scale

Describe condensation

gas to liquid > exothermic

Describe deposition

gas to solid > exothermic

Describe Dalton's Law of Partial Pressure

gases in a mixture behave independently and exert the same pressure they would if they were in the container alone

At constant temperature volume is:

inversely proportional to pressure

What type of crystalline solid has a high melting point, conducts electricity when molten but no as a solid, and is brittle?

ionic solid

Describe evaporation

liquid to gas > endothermic

Trends in Intermolecular Forces

london dispersion: all substances dipole-dipole: also composed of polar molecules hydrogen: also polar containing F, N, O

Describe Vapor Pressure

partial pressure of gas molecules above a liquid/solid when 2 states of in equilibrium

At constant pressure volume is:

proportional to temperature

Define Freezing Point

temperature at which liquid/solid states of a substance are in equilibrium

Define melting point

temperature at which the liquid/solid states of a substance are in equilibrium (identical to freezing point)

Define Normal freezing point

temperature when liquid/solid are in equilibrium at pressure of 1 atm

Define boiling Point

temperature when vapor pressure of liquid equals external pressure

Explain intermolecular forces

the force of attraction *between* molecules > weaker than bonds

The viscosity of different liquids vary- increasing w/ the magnitude of their intermolecular forces/sizes

the viscosity of a liquid decreases as liquid is heated

What is molar volume?

the volume occupied by 1 mole of gas > 22.41

Describe sublimation

vaporization of a solid > endothermic