The Nature of Gases Chapter 10 section 1

Kinetic theory kinetic energy – the energy an object has because of its motion kinetic theory – the tiny particles in all forms of matter are in constant motion

Kinetic Theory of Gases A gas consists of small particles that move rapidly in straight lines have essentially no attractive forces 3

are very far apart have very small volumes compared to the volumes of the containers they occupy have kinetic energies that increase with an increase in temperature

Properties of Gases Gases are described in terms of four properties: pressure (P) volume (V) temperature (T) amount (n) 5

Gas Pressure gas pressure – the force acting on a specific area The force is the result of billions of gas particles simultaneously colliding with the object.

Vacuum – empty space where there are no gas particles, no collisions and therefore no force or pressure.

Atmospheric pressure is the pressure exerted by a column of air from the top of the atmosphere to the surface of the Earth

altitude weather. Is about 1 atmosphere at sea level. Depends on Is lower at high altitudes where the density of air is less. Is higher on a rainy day than on a sunny day.

barometer - device used to measure atmospheric pressure indicates atmospheric pressure as the height in mm of a column of mercury 12

Formula Pressure (P) = force area Pressure units: pascal (Pa) – SI unit millimeters of mercury (mmHg) atmospheres (atm)

standard atmosphere (atm) – pressure required to support 760 mm of mercury in a mercury barometer at 25ºC.

Conversion Factors 1 atm = 760 mmHg (exact) 1 torr = 1 mmHg 1 atm = 760 torr 1 atm = 14.7 lb/in.2 1 atm = 101.325 kPa

Learning Check A. What is 475 mmHg expressed in atmospheres (atm)? 3) 3.61 x 105 atm B. The pressure in a tire is 2.00 atm. What is this pressure in mmHg? 1) 2.00 mmHg 2) 1520 mmHg 3) 22 300 mmHg 16

Solution A. What is 475 mmHg expressed in atm? 2) 475 mmHg x 1 atm = 0.625 atm 760 mmHg B. The pressure of a tire is measured as 2.00 atm. What is this pressure in mmHg? 2.00 atm x 760 mmHg = 1520 mmHg 1 atm 17

temperature temperature is a measure of the average kinetic energy of the molecules that make up a substance. Increase in average kinetic energy causes the temperature to rise Decrease in average kinetic energy causes temperature to drop.

Particles with no kinetic energy have no motion and no temperature. Absolute zero is the temperature at which the motion of particles theoretically stops. Absolute zero = ºK

Kelvin temperature scale reflects the relationship between temperature and average kinetic energy. The Kelvin temperature of a substance is directly related to average kinetic energy of its particles. Particles at 200 ºK have twice the kinetic energy as particles at 100 ºK.

Learning Check A cylinder of oxygen gas is cooled from 300K (27 ºC) to 150 K (-123 ºC). By what factor does the average kinetic energy of the oxygen molecules in the cylinder decrease?

Solution Since there is a direct relationship between Kelvin temperature and average kinetic energy the factor is 150 K = 1 or 300 K = 2 300 K 2 150 K 1

Learning Check Would you expect to find negative temperatures on the Kelvin temperature scale?

Solution Since temperature is a measure of the average kinetic energy (motion) of particles and 0 ºK implies the absence of movement, no.

The Nature of Liquids Chapter 10 section 2

Particles in liquids are in motion free to slide past one another like gases and can flow unlike gases in that they do have intermolecular attractive forces between them hydrogen bonds dipole-dipole interactions

Intermolecular forces cause liquids to have a definite volume rather than being able to fill their containers increasing pressure will not effect the volume of a liquid like solids, liquids are known as condensed states of matter.

vaporization – conversion of a liquid into a gas evaporation – conversion of a liquid into a gas from the surface of a liquid that is not boiling. condensation – conversion of a gas into a liquid

Heat increases the rate of evaporation. Evaporation, however, is a cooling process. The molecules with the highest amount of kinetic energy are the ones that evaporate. With the loss of these molecules, the average amount of kinetic energy is reduced and temperature drops.

Vapor Pressure When liquids are in a closed container, evaporation still occurs. Condensation also occurs. Equilibrium occurs when the number of particles evaporating equals the number of particles condensing. Evaporation Condensation - called - dynamic equilibrium

The gas particles in the closed container exert pressure on the container. Vapor pressure – force due to the collision of the gas particles above a liquid in a closed container.

Vapor pressure increases with increase in temperature. Manometer – device that measures the vapor pressure of a liquid.

When temp reaches a high enough level, most particles in the liquid have the kinetic energy to overcome their intermolecular forces and change into a gas. This causes boiling. Boiling - vaporization throughout a liquid

Boiling point is the temp at which the vapor pressure of the liquid is equal to the external pressure (atmospheric pressure). Bubbles of vapor form inside the liquid and rise to the surface and escape as the liquid boils.

Boiling is cooling process just like evaporation. As a result, temperature of a boiling liquid never rises above its boiling point.

normal boiling point – boiling point of a liquid at a pressure of 101 normal boiling point – boiling point of a liquid at a pressure of 101.3kPa or 1 atm. increases as pressure increases. decreases as pressure decreases.

In Boston which is at sea level where atmospheric pressure is 101 In Boston which is at sea level where atmospheric pressure is 101.3kPa, boiling point of water is 100 ºC. In Denver which is 1600 m above sea level where atmospheric pressure is 85.3kPa, boiling point of water is 95 ºC.

Learning Check Would it take longer to boil pasta in Boston or Denver? Why?

Solution Longer in Denver because boiling water is not as hot. (95 ºC instead of 100)

Learning Check Why do foods cook faster in a pressure cooker?

Solution In a pressure cooker, water boils well above 100 ºC.

The Nature of Solids Chapter 10 section 3

Particles in a solid Tend to vibrate in a fixed position Are packed against one another in a highly organized pattern Have a definite shape and volume

Changes in state melting – solid turns into a liquid freezing – liquid changes into a solid

melting point – temperature at which a solid turns into a liquid freezing point – temperature at which a liquid turns into a solid

For any given solid, the melting point and freezing point are the same temperature. At this temperature, the solid and liquid substance are in equilibrium. Solid Liquid

Most solids are crystals. Crystal – solid substance in which the particles are arranged in an orderly, repeating, 3-dimensional pattern.

The type of bonding that exists between the atoms determines the melting points of crystals. Ionic solids have relatively high melting points Molecular solids (w covalent bonds) have relatively low melting points

Allotropes – 2 or more different molecular forms of the same element in the same physical state. Example; carbon has 3 allotropes

buckminsterfullerine 1985 buckminsterfullerine (buckyballs) discovered. Molecule with 60 or more C atoms arranged into a structure like a soccer ball.

diamond Buckminsterfullerene -buckyball graphite

amorphous solids – non-crystalline solids whose atoms are randomly arranged. Examples: rubber, plastic, asphalt, glass

Changes of State Chapter 10 Section 4

Heat of Fusion the amount of heat released when 1 gram of liquid freezes (at its freezing point) the amount of heat needed to melt 1 gram of a solid (at its melting point) 55 55

for water (at 0 °C) Heat of = 334 J or 80 cal Fusion 1 g of water

Calculations Using Heat of Fusion How much heat in calories is needed to melt 15.0 g of ice at 0 °C ? STEP 1 Given: 15.0 g of water(s) Change of state: melting at 0 °C 58 58

STEP 2 Plan: g of water(s) g of water(l) STEP 3 Write conversion factors: 1 g water = 80 cal 1 g water and 80 cal 80 cal 1 g water

Set up the problem to calculate calories: STEP 4 Set up the problem to calculate calories: 15.0 g water x 80 cal = 1200 cal 1 g water 60 60

Learning Check How many joules are released when 25.0 g of water at 0 °C freezes? 1) 334 J 2) 2000 J 3) 8350 J 61 61

Solution STEP 1 Given: 25.0 g of water (l) change of state: freezing at 0 °C STEP 2 Plan: g water (l) g of water (s) 62 62

STEP 3 Write conversion factors: 1 g of water = 334 J 1 g of water and __334 J___ 334 cal 1 g of water

Set up the problem to calculate joules: STEP 4 Set up the problem to calculate joules: 25.0 g water x 334 J = 8350 J (3) 1 g water 64 64

Sublimation occurs when a solid changes directly to a gas takes place in frost-free refrigerators is used to prepare freeze-dried foods for long-term storage 66 66

dry ice (solid CO2) sublimes at 78 C

condenses when gas molecules lose energy and form a liquid Water evaporates when molecules on the surface gain sufficient energy to form a gas condenses when gas molecules lose energy and form a liquid 69 69

Water boils when molecules acquire the energy to change into a gas forming bubbles throughout the liquid 70 70

Heat of vaporization the amount of heat absorbed to vaporize 1 g of a liquid to gas at the boiling point the amount of heat released when 1 g of a gas condenses to liquid at the boiling point

Boiling Point of Water = 100 °C Heat of = 2260 J or 540 cal Vaporization 1 g of water (water) 72 72

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Learning Check How many kilocalories (kcal) are released when 50.0 g of water(g) as steam from a volcano condenses at 100 °C? 1) 27 kcal 2) 540 kcal 3) 2700 kcal 74 74

Solution STEP 1 Given: 50.0 g of water(g) Change of state: condensing at 100 °C STEP 2 Plan: g of water(g) g of water(l) 75 75

Write conversion factors: 1 g of water = 540 cal STEP 3 Write conversion factors: 1 g of water = 540 cal 1 g of water and 540 cal 540 cal 1 g of water 1 kcal = 1000 cal 1 kcal and 1000 cal 1000 cal 1 kcal

Set up the problem to calculate kilocalories: STEP 4 Set up the problem to calculate kilocalories: 50.0 g water x 540 cal x 1 kcal = 27 kcal 1 g water 1000 cal 77 77

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Phase diagram diagram that gives the conditions of temperature and pressure at which a substance exists as a solid, liquid and gas. Lines separating regions (phases) give the conditions in which the two phases exist in equilibrium

For water triple point is triple point – on a phase diagram, the temperature and pressure at which all three phases can exist in equilibrium with one another. For water triple point is 273.16 ºK or 0.01 ºC Vapor pressure – 611.73 pascals

For Water

A heating curve Illustrates the changes of state as a solid is heated. Uses sloped lines to show an increase in temperature. Uses plateaus (flat lines) to indicate a change of state.

Learning Check A. A flat line on a heating curve represents 1) a temperature change 2) a constant temperature 3) a change of state B. A sloped line on a heating curve represents

Solution A. A flat line on a heating curve represents 2) a constant temperature 3) a change of state B. A sloped line on a heating curve represents 1) a temperature change

A cooling curve Illustrates the changes of state as a gas is cooled. Uses a sloped line to indicate a decrease in temperature. Uses plateaus (flat lines) to indicate a change of state.

Learning Check Use the cooling curve for water to answer each. A. Water condenses at a temperature of 1) 0°C 2) 50°C 3) 100°C B. At a temperature of 0°C, liquid water 1) freezes 2) melts 3) changes to a gas C. At 40 °C, water is a 1) solid 2) liquid 3) gas D. When water freezes, heat is 1) removed 2) added

Solution Use the cooling curve for water to answer each. A. Water condenses at a temperature of 3) 100°C B. At a temperature of 0°C, liquid water 1) freezes C. At 40 °C, water is a 2) liquid D. When water freezes, heat is 1) removed