Behavior of Gases

• C-5: The student will demonstrate an understanding of the structure and behavior of the different phases of matter.

C-5.1 Explain the effects of the intermolecular forces on the different phases of matter.

EQ 1. What are the phases of matter?

EQ 2. What are intermolecular (or interparticle forces)?

EQ 3. In the phases of matter listed above, are these forces strong, intermediate, or weak?

Phases of Matter

• Kinetic model of solids: Strong forces between particles keep structure rigid. They are in motion but cannot move past one another. Crystal lattice is the three-dimensional arrangement of the particles in a solid.

• Kinetic model of liquids: Interparticle forces maintain their volume, but not their shape. Particles are so close together they slide past one another. i.e. magnetized marbles.

• Kinetic Model of gases: Interparticle forces do not maintain shape or volume. Particles “bounce” off each other. Gases do not lose kinetic energy as they bounce off each other or the container. The collisions are elastic.

Other phases of Matter?

• Other forms of matter: matter that looks like a solid or gas but behave like a liquid. These forms are plasmas, liquid crystals, and amorphous materials.

• What are some examples of the other forms of matter?

• Liquid crystals - laptop, calculators• Plasma – ionized gas, i.e. sun, stars, fluorescent

lights• Amorphous Materials – disjointed, and incomplete

crystal lattice. i.e. peanut butter, wax, cotton candy

EQ4. What is the Kinetic Molecular Theory for gases?

• Kinetic Theory of Matter: states that all submicroscopic particles of all matter are in constant random motion. The energy of moving objects is called kinetic energy.

• Kinetic Model of gases: Gases do not lose kinetic energy as they bounce off each other or the container. The collisions are elastic.

• A gas with particles in constant random motion in which they have no attraction for each other are called ideal gases. Nearly all gases are ideal except when they are at very low temperatures or very high pressures. Pressure is the force acting on a unit area.

Indicator C-5.2

• Explain the behaviors of gas; the relationship among pressure, volume, and temperature; and the significance of the Kelvin (absolute temperature) scale, using the kinetic-molecular theory as a model.

EQ 5. What is pressure, volume, and temperature?

• Pressure - _____ _______________

• Volume - _______

______________

• Temperature- ____ ________________

EQ 6. How do pressure, volume and temperature effect gases?

• Pressure is what keeps the balloon inflated.• Atmospheric Pressure is 760 mm of Hg = 1atm

(is the pressure on us now.)• If pressure increases, the volume decreases. If

pressure decreases, the volume____?____.• List the other pressure units:

• If pressure is doubled, the volume decreases by half.

Pressure Units

• 1 atm = 760 mmHg (torr) = 101.3 kPa = 14.7 psi• Conversions:

– What pressure, in kPa, atm, and psi does a gas exert at 246 mm Hg?

– 246 mm Hg x 101.3 kPa = 32.8 kPa

760 mm Hg

246 mm Hg x 1 atm = 0.324 atm

760 mm Hg

246 mm Hg x 14.7 psi = 4.76 psi

760 mmHgPressure conversions. (Cp -p. 387. TP – p. 339 )

EQ 6. How does pressure, volume and temperature affect gases?

• Gas is heated (temperature increases) – average kinetic energy increases, particles’ speed increases.

• Gas is cooled (temperature decreases) – average kinetic energy decreases, particles’ speed decreases.

• How do we measure temperature?

Three scales: Fahrenheit, Celsius, and Kelvin

°C = (° F-32) x 0.556 °F = (°C x 1.8) + 32

Tk = (Tc + 273) K Tc = (Tk - 273) °C

p. 78 CP TP p.66-71

Temperature Conversions

• Convert 60.4 °C to Kelvin – Tk = (Tc + 273) K– Tk = 60.4 + 273) K = 333 K

Convert 76.5 °F to Kelvin

°C = ( °F-32) x 0.556

°C = (76.5 °F -32) x 0.556 = 24.7

Tk = 24.7 °C + 273 = 298 K

EQ7: What is absolute (zero) temperature?

• Absolute Zero – the temperature at which a substance has no kinetic energy. No particles are moving. This is:

0 Kelvin, -273.15 °C, -459.67 °F.

Why is the Kelvin scale important?

EQ7: What is absolute (zero) temperature?

Why is the Kelvin scale important?

It is the temperature at which the average kinetic energy of gas particles would be theoretically zero. Thus absolute zero.

EQ8. How are the relationships described mathematically?

• Boyle’s Law:

P1 x V1 = P2 x V2

If pressure is doubled, the volume decreases by half.

• Sample problem 3, p.388.

• Charles’s Law V1 = V2 , pressure and mass is constant

T1 T2 If temperature is increased, then volume increases.

Boyle’s Law:

• The pressure-volume relationship:

Pressure and volume is inversely related, temperature and mass is constant.

Charles’s Law

• The temperature – volume relationship:

• V1 = V2 ,

• T1 T2

• V1 xT2 = V2 xT1

• Pressure and mass is constant

If temperature increase, then volume increases.

Sample problem 5, p.393(cp)

Combined Gas Law:

• P1 x V1 = P2 x V2

T1 T2

• P1V1T2 = P2V2T1

• This gas law is a combination of which gas laws?

Standard Temperature and Pressure

(STP)

• Standard Temperature = 0º C = 273K

• Standard Pressure = 1 atm = 14.7 psi

=760 mm Hg (torr) = 101.3 kPa

Ideal Gas Law:

• PV = nRT

• R (constant) =(8.31 kPa ∙ L) not variables

• mol ∙ K• P = pressure (kPa) V = volume (Liters)

• n = # of mole T = temperature (Kelvin)

Indicator C-5.4

• Illustrate and interpret heating and cooling curves (including how boiling and melting points can be identified and how boiling points vary with changes in pressure).

EQ9. How can boiling points and melting

points be identified from graphs? Melting and Boiling points of Water

-40

-20

0

20

40

60

80

100

120

Time (min.)

Tem

p. (C

elsi

us)

• When the temperature stops increasing. (The line flattens.)

• Define Heat of Fusion.

• Define Heat of Vaporation.

Heating and Cooling curve of Acetone

• Graph the following points:Time (min.) vs Temperature, °C

0 -115

5 -95.35

10 -95.35

15 -95.35

20 0 °C

30 18

35 36

40 56.24

45 56.24

50 56.24

Heating Curve of Acetone

-140-120-100-80-60-40-20

020406080

0 10 20 30 40 50 60

Time (min.)

Deg

rees

Cel

sius

Cooling Curve of Acetone

-140-120

-100-80-60

-40-20

02040

6080

0 10 20 30 40 50

Time (min.)

Tem

p. C

elsi

us

EQ10: How does pressure affect boiling points?

• Boiling Point – the temperature of a substance when its vapor pressure equals the pressure exerted on the surface of the liquid.

• Vapor Pressure – the pressure of a substance in equilibrium with its liquid. Particles are evaporating and condensing at the same rate.

• Low vapor pressure substances have high boiling points. i.e. mercury, syrup. Interparticle forces are strong.

• High vapor pressure substances have low boiling points. i.e. ethanol, perfume. Interparticle forces are weak.

EQ10: How does pressure affect boiling points?

• If pressure increases, the temperature increases. Thus, the boiling point of a substance will increase.

• What cooking device uses this concept?

Answers

EQ 1. Solid, liquid, gases, etc.

EQ 2. - attraction between the molecules.

EQ 3. Solids - strong,

Liquids - intermediate,

Gases - weak

EQ 5. What is pressure, volume, and temperature?

• Pressure is the force acting on a unit area.

• Volume is the space occupied by a sample of matter.

• Temperature is the measure of the average kinetic energy of particles.

Definitions

• Heat of Fusion – the amount of energy needed to change a material from the solid state to the liquid state.

• Heat of Vaporation – the amount of energy needed to change a material from the liquid to the gas state.