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www.njctl.org

Unit 5

States of MatterPart B: Solids, Liquids & Gases

AP Chemistry

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States of Matter

The liquid state of water is very rare in the universe. It is most commonly found as a solid (Mars, Moon, Comets) or as a gas.

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Solids, Liquids, and GasesThe properties of each state differ from each other

considerably.

Property Solid Liquid Gas

Compressibility Very Low Very Low High

Density High High LowViscosity Super High Medium Very Low

Potential Energy Low Medium High

Note: Water is unique in that its liquid state is more dense than the solid state.

Recall that viscosity is the resistance to flow. The weaker the particle interactions, the lower the viscosity.

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Solids, Liquids, and Gases

The properties of a material will vary depending on its state.

Electrical Conductivity of NaCl

NaCl(s) = Non-conductive

NaCl(l) = Conductive

Density of H2O

H2O(l) @ 0 C = 999 g/L

H2O(g) @ 0 C = 0.804 g/L

Viscosity of H2O

H2O (l) @100 C = 0.664 u

H2O (g) @100 C = 0.011 u

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Solids, Liquids, and Gases

Class Discussion

Can you explain why the viscosity of water is so much less in the gas state?

The Coulombic attractions are much weaker so the molecules demonstrate

very little resistance to the sheering forces that cause molecules to flow

past one another.

move for answer

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SolidsThe properties of a solid are determined by the nature of the elements that constitute it. There are essentially four types of solids that differ considerably in their make-up and properties.

Ionic Solids: salts

Metallic Solids: copper, gold

Covalent Network Solids: diamonds, graphite

Covalent Molecular Solids: solid CO2, table sugar, ice

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Solids

Ionic Solids (Example: NaCl)

Formed from elements with large differences in electronegativity resulting in ions.

Have high melting points due to their strong intramolecular forces

MP of NaCl = 801 Celsius

Are brittle due to the inflexibility of these forces

Conduct electricity only in liquid state where ions are free to move

++

++

++

+

--

--

-

-

---

- -Cl- ion

Na+ ion

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SolidsMetallic Solids (Example: Cu)

Formed from metallic elements with similar electronegativities

Since metals have low effective nuclear charges, the outer valence electrons are lost creating metals ions.

The lost electrons are de-localized and can move easily within the crystal making the metal conductive in all states.

Have high melting points due to their intramolecular forces

MP of Cu = 1085 Celsius

Are malleable due to the flexibility of the unique non-directional covalent bonds

++

+++

++

+-

-

--

--- --

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SolidsCovalent Network Solids (Example: C(diamond))

Non-metallic atoms bound to each by covalent bonds creating a single giant macromolecule.

Due to the high effective nuclear charges of the atoms involved, the electrons are localized and not mobile so generally they are

non-conductive (sp2 hybridized graphite is an exception due to pi bonds)

High high melting points due to intra-molecular forces

MP Diamond = 4827 Celsius

diamond (sp3 hybridized C atoms)

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SolidsCovalent Network Solids - Allotropes

Different molecules made of same element are called allotropes.

C(diamond) C(graphite)

sp3 hybridized

non-conductive

one giant molecule

sp2 hybridized

conductive

layers of molecules connected by weak intermolecular forces

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Solids

Covalent Molecular Solids (Example: CO2)

Composed of many covalently bonded molecules each composed of non-metals.

covalent bonds (intra)LDF's (inter)

The molecules are held together by relatively weak inter-molecular forces resulting in low melting and

boiling points compared to the other solids.

Since the atoms involved have relatively high effective nuclear charges, the electrons are localized making these

solids poor conductors.

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SolidsWhen comparing melting and boiling points, consider the nature

of the solid and the factors that influence the strength of the particle interactions.

Rank the substances by order of increasing melting point.

C6H14 K Li First determine the nature of the material and interactions

C6H14 molecular (inter, non-polar, LDF's)

K metallic (intra, covalent)

Li metallic (intra, covalent)

Since hexane has inter-molecular forces it will have lowest melting point.

Since Li has smaller atomic radii than K, it's coulombic attractions will be stronger yielding the highest melting point.

C6H14 < K < Limove to to see answer

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1 Which of the following states of matter would have the lowest viscosity?

A Solid

B Liquid

C Gas

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2 Which of the following is NOT true regarding the liquid state?

A It is significantly more compressible than the solid state

B The viscosity is less than the solid state

C The density is less than the solid state for most materials

D The Coulombic attractions are weaker than in the solid state

E The potential energy of the molecules is less than in the gas state

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3 Which of the following would be TRUE when a gas condenses?

A It will become more compressible

B It will become less dense

C The coulombic attractions will decrease

D The viscosity will decrease

E The potential energy of the molecules will decrease

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4 Which of the following substances would be characterized by delocalized electrons and high melting points?

A KF

B Cu

C CO2

D C(diamond)

E None of these

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5 Which of the following would be characterized by high electrical conductivity?

A KF(s)

B KF(l)

C C(diamond)

D H2O(s)

E H2O(l)

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6 Which of the following correctly ranks the solids by increasing melting point?

A H2O < CH4 < BeO < NaF

B CH4 < H2O < BeO < NaF

C CH4 < H2O < NaF < BeO

D BeO < NaF < CH4 < H2O

E CH4 < NaF < BeO < H2O

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7 Which of the following would correctly rank the substances below from lowest to highest boiling points at 1 atm?

A I2 < Br2< F2

B Li < Na < K

C NaCl < NaBr < NaI

D C3H8 < H2 < O2

E None of these

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LiquidsLiquids distinguish themselves from the solid phase by the

ability to flow due to diminished coulombic attractions between particles.

Hydraulic systems take advantage of a liquids ability to take

the shape of its container and low compressibility to

exert a force.

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Liquids

The viscosity of a liquid is influenced by the strength of the Coulombic attractions between particles.

H2O CH3COCH3 C6H6

Types of attractions

weak LDF's, H-

Bonds

medium LDF's, weak DDF's Strong LDF's

Viscosity (m Pa*s) 0.892 0.308 0.602

Comparing three molecular liquids

*Note: Recall LDF stands for London Dispersion Forces

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LiquidsThe viscosity of a motor oil is critical to correct engine

performance.

For instance a 0W-40 oil indicates that the oil will stay thicker (higher viscosity) at both 0C and 100 C than does oil rated as 5W-30.

Engine oil ratings indicate the resistance to flow at 0C and at 100 C.

If the oil gets too thin, it will not lubricate adequately and goodbye engine!

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8 Which of the following is TRUE regarding viscosity?

A The stronger the coulombic attractions, the lower the viscosity

B The higher the temperature, the higher the viscosity

C Solids have lower viscosities than liquids

D A substance with a low viscosity will flow easier than one with a high viscosity

E None of these

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9 Which of the following liquids would be expected to have the highest viscosity?

A CH3COCH3

B C6H14

C C4H10

D CH3CH2CH2OH

E All would have the same viscosity

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10 Which of the following make gases unsuitable to use in hydraulics?

A They are too viscous

B The Coulombic attractions are too strong

C The gas state is too compressible

D The gas state cannot flow

E None of these

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Gases

The kinetic molecular theory forms the basis for our understanding of particles in the gas state.

Assumption 1:

Gas molecules occupy a negligible volume of their container. So... the volume of a gas is assumed to be equal to the volume

of the container. Gas

molecules

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GasesThe kinetic molecular theory forms the basis for our

understanding of particles in the gas state.

Assumption 2:

Gas molecules are in constant motion and routinely collide with each other and with the walls of the container thus exerting a

pressure whose magnitude depends on the frequency and forcefulness of these collisions.

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GasesThe kinetic molecular theory forms the basis for our

understanding of particles in the gas state.

Assumption 3:

Each gas molecule does not experience any Coulombic attractions from the other gas molecules or container and

therefore do not "stick" to each other, resulting in collisions that are perfectly elastic.

Note: Some of these assumptions assume "Ideal" behavior of a gas and must be modified somewhat for "Real" gases. We will

deal with this distinction later.

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Basic Gas LawsThe temperature of a gas is equivalent to the average kinetic

energy of the gas molecules.

At a given temperature, the gas molecules possess a wide range of kinetic energies. This is known as the Boltzmann distribution.

The higher the temperature, the greater the speed of the gases, the greater the kinetic energy.

*Note: Even at low temperatures, some of the gas molecules have as much energy as the average energy of the gas molecules at a much higher temperature.

# of gas molecules

Molecular speeds

Temperatures

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Basic Gas Laws

The pressure of a gas is directly proportional to the Kelvin temperature and the number of moles.

The higher the temperature, the greater the speed and kinetic

energy of the molecules thereby increasing BOTH the frequency

and force of each collision thereby increasing the pressure.

P

T (K)

The greater the number of moles of a gas, the

greater the frequency of collisions and the higher

the pressure.

P

moles

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Basic Gas Laws

The pressure of a gas is inversely proportional to the volume.

As the volume increases, the collisions become less numerous and the pressure decreases.

less collisions more collisions

Pressure

Volume

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Basic Gas Laws

The volume of a gas is directly proportional to the Kelvin temperature and the number of moles.

As the temperature increases, the volume must expand against a constant pressure.

V

T (K)

As the number of moles are increased, the volume will expand

against a constant pressure.

V

moles

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Basic Gas LawsThe relationships between the various qualities of a gas can

be used to predict the change in the pressure, volume, moles, or temperature of a gas.

Example: What would be the effect on the volume of a gas if the pressure were doubled and the temperature were increased from

10 C to 20 C? SOLUTION

V and P are inversely related, V and T are directly related

Since P doubled, volume will decrease by factor of two.

Since K temperature increased by 293/273, the volume will increase by 293/273.

1 L x 1 atm x 293 K = 0.52 L

2 atm 283 K

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11 Which of the following is a correct assumption of the kinetic molecular theory of gases?

A Gases do not collide with each other

B Gases collide but lose energy with every collision

C Gases experience weak coulombic attractions between molecules

D A gas occupies a neglible volume of their container

E None of these

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12 Which of the following influence the pressure of an ideal gas?

A The frequency of collisions

B The frequency and force of collisions

C The force of collisions

D Neither the frequency or force of collisions

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13 Which of the following is NOT TRUE regarding a gas?

A All N2 gas molecules will have the same kinetic energy at a given temperature

B The volume of a gas is directly related to it's kelvin temperature

C If the Kelvin temperature of a gas is doubled, the pressure will double all else being constant

D Collisions between gas molecules are elastic

E Coulombic attractions between gas molecules are considered neglible.

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14 A 9 L expandable container containing a gas is heated in an isobaric manner (constant pressure) from 17 C to 117 C. What would be the new volume at 117 C?

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15 A gas in a rigid container registers a pressure of 3.2 atm at 0 C. If the temperature is cooled to -20 C, which of the following would be TRUE?

A The volume of the container will decrease.

B The inter-molecular distances will increase

C The average kinetic energy of the gas molecules will increase

D The frequency of collisions will decrease

E None of these

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16 A flexible balloon is dropped out a spaceship on Mars. Inside the spacecraft, the balloon has a pressure of 0.6 atm, a temperature of 20 C, and a volume of 18 L. What would be the new volume of the balloon if the pressure on Mars was 0.08 atm and the temperature was -30 C?

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17 Examine the container below which consists of two glass flasks connected by a valve. What is the pressure of the helium gas after the valve has been opened?

valve

2 L of He @ 2atm 0.8 L of Ar @1 atm

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Density of Gases

The density of a gas is inversely proportional to its volume

Example: A sample of oxygen gas has a density of 1.43 g/L @ STP. What will be the new density if the gas is compressed

isothermally to a new pressure of 1100 mm Hg?

SOLUTION

Volume and pressure are inversely related.

Since pressure increases by 1100/760, the volume will decrease by 760/1100 and the density will increase by 1100/760.

1.43 g/L x 1100 mmHg = 2.07 g/L

760 mm Hg

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18 A 0.5 mole sample of helium gas in an isobaric chamber is heated from 100 C to 300 C. What is the density of the gas at 300 C if the gas occupies a volume of 2 L at 100 C?

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19 A gas is heated from 100 K to 300 K and the pressure is dropped from 100 mbar to 50 mbar. Which of the following would be TRUE regarding the density?

A The density will inrease by a factor of 3

B The density will decrease by a factor of 3

C The density will increase by a factor of 6

D The density will decrease by a factor of 6

E The density will increase by a factor of 3/2

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20 Oxygen gas has a density of 1.43 g/L @STP. Hydrogen gas has a density of 0.098 g/L @STP. To what pressure (in atm) must the hydrogen gas be raised to increase its density to be equal to that of oxygen? Assume a rigid container and isothermal compression.

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Ideal Gas LawThe ideal gas law expresses the relationships of the pressure,

volume, temperature, and mole amounts of a gas.

PV = R (Ideal gas constant) = 0.0821 L*atm/mol*K

nTPV = nRT

If 3 of the 4 quantities are known, the 4th can be easily calculated.

Recall that 760 mm Hg = 1 atm = 760 torr = 101.3 kPa

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21 What is the mass of a sample of argon gas @ a temperature of 15 C, a pressure of 450 mm Hg, and occupying a 120 mL container?

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22 What is the volume of a 32 gram sample of O2 gas @ 0 C and 760 torr?

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23 At what temperature would a 87 gram sample of xenon gas be at 450 torr pressure and occupying a 2.5 L container?

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24 What is the density of a sample of chlorine gas @ 300 K and a pressure of 1.6 atm? (Remember that the molar mass of a gas is the mass (g) of 1 mole (n) of a substance)

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Molar Mass and Molar VolumeThe molar mass of a gas is equal to the ratio of the mass to moles (grams/mol). The molar volume of a gas is equal

to the ratio of the volume to moles (L/mol).

The molar mass of a gas can be determined often by using PV=nRT to find the moles if the mass is known.

The molar volume varies with temperature and pressure so the volume must first often be determined.

@STP 1 mol of any gas = 22.4 L

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25 A gas has a vapor density of 1.23 g/L @15 C and 1 atm pressure. What is the formula of the gas?

A CH4

B CCl4

C CH3Cl

D C2H6

E NH3

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26 A 22.50 gram sample of a gas in a 2.50 L container @ -4 C exerts a pressure of 4.52 atm. Identify the gas.

A O2

B Ar

C CO2

D NH3

E Cl2

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27 Identify the gas in which a 42 gram sample occupies 33.6 L @STP.

A CO2

B CH4

C O2

D N2

E He

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28 A 36 gram sample of helium gas exerts a pressure of 450 mm Hg @ 10 C. What is the molar volume of the gas at these conditions?

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29 Oxygen gas is collected by dispensing it from a gas cylinder into a previously evacuated tube. Use the data below to find the molar volume of the gas @STP.

Mass of cylinder initially = 110.400 grams

Mass of cylinder after dispensing gas = 110.273 grams

Volume of gas dispensed @ 15 C = 100.3 mL

Pressure of gas collected @ 15 C = 763 mm Hg

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Law of Partial Pressures

The total pressure of mixture of gases is equal to the sum of the partial pressures of each gas.

Ptot = PA + PB + PC ....

Since moles and P are directly related it follows that:

Ntot = NA + NB + NC ....

The relationship between pressure and moles is often conveniently expressed as:

PA = NA

PTOT NTOT

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Law of Partial PressuresInsoluble gases such as CO2, H2, or C4H10 can be easily

collected over water. When doing so, water vapor becomes mixed with the collected gas.

H2(g) and H2O(g)

Mg(s) + 2H+(aq) --> H2(g) + Mg2+(aq)

trough

The H2 gas produced in RXN moves through the tubes and bubbles into a collection flask and displaces the water.

When the water level in the collection flask and trough are equal, the pressure of the gases (H2 and H2O) must be

equal to atmospheric pressure.

The partial pressure of the H2(g), often called the "dry gas" is obtained by subtracting the water vapor pressure at that

temperature from the atmospheric pressure.

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30 Air is roughly 79% by mole amount nitrogen gas, 20% oxygen by mole amount, and 1% other trace gases. What is the partial pressure of oxygen gas in an air sample with a pressure of 745 torr?

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31 A sample of butane gas (C4H10) is collected over water @ 17C. The vapor pressure of water at this temperature is 16.4 mm Hg. What is the partial pressure of butane collected if the total pressure is 762 mm Hg?

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32 A sample of He, Ar, and Ne at 10 C contains 10 grams of each gas. Which of the following would be TRUE of the mixture?

A There is an equal number of moles of each gas

B Each gas would exert the same partial pressure

C Each gas would have have the same average kinetic energy

D Each gas would have equal number of molecules in the sample

E None of these are true

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33 What is the partial pressure of hydrogen gas if a mixture containing 4 grams of H2, 16 grams of O2, and 17 grams of NH3 exerts a total pressure of 1.2 atm?

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Graham's Law of EffusionThe speed of a gas is inversely proportional to the square

root of the mass.

For gases at the same temperature...

KEa = KEb ----> mava2 = mbvb

2 ----> ma = vb2

mb va2

This law can be practically viewed two ways:

1. A gas that is twice as heavy will move 2(1/2) or 1.41 x slower.

2. A gas that is twice as fast must be 22 or 4x lighter.

Effusion refers to the random movement of gas molecules through a small opening.

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Graham's Law of EffusionThe speed of a gas is inversely proportional to the square

root of the mass.

Example: What is the molar mass of a gas that travels at four times the speed of chlorine gas?

4 x speed = 42 x lighter = 16 x lighter

Cl2 = 70 g/mol divided by 16 = 4.3 g/mol

Example: How much faster would helium move compared to neon?

Ne is 20/4 or 5 x heavier than He so will move 5(1/2) or 2.23 x slower than He.... or He will move 2.23x faster than Ne.

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34 A container filled with 2 moles each of Ar, Ne, and NH3 is punctured creating a small hole. Which of the following would be the correct order of the gases inside the container after 2 hours have passed?

A NNH3 > NNe > NAr

B NAr > NNH3 > NNe

C NNe > NAr > NNH3

D NAr > NNe > NNH3

E NNH3 > NAr > NNe

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35 Which of the following gases will travel at approximately 2.5x the speed of Xe?

A O2

B Ne

C H2

D SiH4

E CO2

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36 How much slower will carbon dioxide move compared to ammonia (NH3)?

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37 Two samples of gases (oxygen and hydrogen) occupy the same amount of space at the same temperature and pressure. Which would NOT be true?

A Both gases have the same average kinetic energy

B Both gases have the same average molecular speed

C Both gas samples have the same number of molecules

D The mass of each gas sample would be different

E The density of each gas sample would be different

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Ideal vs. Real GasesAll gases are real and therefore do not fully conform to our

assumptions of ideal gases.

Real gases do occupy a very small part of their container.

Therefore the volume that we measure is too large, the gas molecules are actually taking up some of the room!

The larger the gas molecule, the more real and less ideal it behaves. For example, C3H8(g) will behave less ideal than H2(g)

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Ideal vs. Real Gases

All gases are real and therefore do not fully conform to our assumptions of ideal gases.

Real gases do experience coulombic attractions/repulsions between molecules.

These attractions and repulsions cause the molecules to take the scenic route and collide less frequently making the measured

pressure less than the ideal. The greater the inter-molecular forces, the less ideal

and more real the gas will behave.

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Ideal vs. Real Gases

Gases behave most ideal (less real) at high temperatures and low pressures.

The greater the inter-molecular forces, the less ideal and more real the gas will behave.

At high temperatures, the gas molecules move too fast to form coulombic attractions making them behave more ideally.

At low pressures, the volume of the container is large thereby making the molecules occupy a non-existent fraction of it making

them behave more ideally.

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38 Which of the following is TRUE regarding real gases?

A I only

B II only

C III only

D I and II only

E I, II, and III

I. Their measured pressure is less than an ideal gas

II. Their measured volume is higher than that of an ideal gas

III. They experience coulombic attractions/repulsions

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39 Which of the following gases would behave most ideally?

A CO2

B N2

C CH4

D He

E Kr

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40 Which of the following gases would behave most real?

A NH3

B CO

C CO2

D F2

E Ne

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41 Which of the following gases and set of conditions will behave most ideally?

AB

CD

E

Gas Temperature Pressure

H2O 500 K 3 atmH2O 100 K 0.1 atmH2O 100 K 3 atmCH4 500 K 3 atmCH4 500 K 0.1 atm

Ans

wer

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Comparing Gas SamplesWhen comparing gas samples, it is critical to remember all of

the relationships.

Examine the three gas samples below

Temp: 20 C 20 C 20 C

Gas: N2 O2 He

Pressure: 1 atm 2 atm 1 atm

Volume: 5 L 5 L 5 L

Which gas sample must have the highest mole value?

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42 Which sample would have the highest number of molecules? A B C

D All have the same number of molecules

E Not enough information

Temp: 20 C 20 C 20 C

Gas: N2 O2 He

Pressure: 1 atm 2 atm 1 atm

Volume: 5 L 5 L 5 L

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43 Which sample would have the fastest moving gas molecules?

A B C

D All gas molecules will move at the same speed at this temperature

E Not enough information

Temp: 20 C 20 C 20 C

Gas: N2 O2 He

Pressure: 1 atm 2 atm 1 atm

Volume: 5 L 5 L 5 L

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44 Which sample would would have the highest density?

A B C

D All would have the same density

E Not enough information

Temp: 20 C 20 C 20 C

Gas: N2 O2 He

Pressure: 1 atm 2 atm 1 atm

Volume: 5 L 5 L 5 L

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Looks like we've run out of gas on this unit! See you in the next unit

where we will deal with mixtures of materials.

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