gasesnotes

.doc

School

University of Texas *

*We aren’t endorsed by this school

Course

PHYSICAL C

Subject

Chemistry

Date

Nov 24, 2024

Type

doc

Pages

20

Uploaded by MagistrateLyrebird3951

Report
Gases SOLID LIQUID GAS Chemical Reactivity of Gases Gases can often be classified into groups based on their chemical reactivity. These groups of gases behave in the same way when in contact with heat, light or another substance showing their characteristic properties. Examples: Noble (Inert Gases) – He, Ne, Ar, Kr, Xe, Rn – low chemical reactivity (chemically stable) Halogens – Fluorine (F 2 ) and Chlorine (Cl 2 ) – highly reactive gases (chemically unstable) Technological Applications: Combustion, Oxidizing, Toxic, Flammable, Corrosive, Compressed Gases Why are gases chemically reactive? Chemical reactivity depends on the electron configuration of its atoms and the strength of attraction between the nucleus and the valence electrons in the outermost shell. The reason why the noble gases are chemically stable is because their valence shell is full (ex. Helium valence shell is filled with two valence electrons and Neon’s valence shell is filled with 8 valence electrons) Draw the Bohr-Rutherford Diagrams for Helium and Neon: Fluorine (F 2 ) and Chlorine (Cl 2 ) are halogen gases and are highly reactive because they are missing one electron in their valence shell. Draw the Bohr-Rutherford Diagrams for Chlorine and Fluorine: Another reason for differences in the reactivity of gases is based on the strength of the bonds between the atoms in a molecule.
Examples: N 2 – is non reactive because of the very strong covalent triple bond between the nitrogen atoms. F 2 – is very reactive because the bond between the 2 Fluorine atoms is weak and easy to break. Note: The diatomic gases are I 2 H 2 N 2 Br 2 O 2 Cl 2 F 2 ( I H ave N o Br ight O r Cl ever F riends) Combustible Gases One of the most common types of oxidation reactions is combustion. The heat released from the reaction has many applications in the home like heating and cooking. In order to have a combustion reaction you must have the three components of the fire triangle: a fuel (hydrocarbons), oxygen, and heat. Alison’s Story
For Bunsen burners when the flame is the optimal mix of fuel and oxidizer it will have a bluish colour because only CO 2 and water will be present. Incomplete combustion will be a yellow colour.
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
  • Access to all documents
  • Unlimited textbook solutions
  • 24/7 expert homework help
Electrolysis of Water Water can be split into hydrogen and oxygen using electricity. 2 H 2 O( l ) → 2 H 2 ( g ) + O 2 ( g ) Researchers are interested in finding an environmentally friendly way to use electrolysis in order to split water and produce hydrogen. Electrolysis is also used to generate oxygen from sea water in submarines. H 2 – characteristic “POP” when exposed to a wooden splint, we call hydrogen a clean fuel because when it is combusted it produces water ( 2H 2 (g) + O 2 (g) → 2H 2 O(g) + heat ) O 2 – will relight a glowing splint and is the most common oxidizer on earth. Oxidizing Gases Oxidizing gases are not limited to just oxygen, Ozone ( O 3 ) is a toxic oxidizer which is actually very helpful to us, but only at high altitude (ozone layer in stratosphere). At ground level it is a main component of smog that causes respiratory problems. Fluorine (F 2 ) and Chlorine (Cl 2 ) – are extremely reactive and can cause serious damage to skin and lung tissue. For this reason it is handled with great caution. Examples of applications: Fluorine (F 2 ) – fluoride ion is an additive in toothpaste (helps with remineralization). Chlorine (Cl 2 ) – chloride ion is used for water purification, the production of plastic (including PVC) and the manufacture of disinfectants. Anode Cathode
PROPERTIES OF GASES 1) No definite shape or volume (will fill any container) 2) Undergo compression 3) Undergo expansion 4) Exert pressure 5) Low density (particles are spread out) 6) Diffuse-Diffusion is when substances move from high to low concentration 7) Gases will mix freely (move quickly) THE 5 POSTULATES OF THE KINETIC MOLECULAR THEORY (KMT) 1. The particles in a gas are infinitely small and have no volume. The gas particles are tiny in comparison to the spaces between them. The volume of the particles is negligible and assumed to be zero. 2. Gases are in constant random motion (Brownian motion). The motion is in straight lines and in all directions 3. Gases don't experience intermolecular forces. The attractive and repulsive forces are negligible (NOT TRUE but they are so small that they can be safely ignored) 4. Gases undergo perfectly elastic collisions. The collisions between gas particles are perfectly elastic, when they collide no energy is lost or gained The particles collide with one another and the sides of the container (creates pressure) 5. Kinetic energy (energy of motion) of particles is directly proportional to temperature (Kelvin). When you increase temperature of a gas it will increase it's average kinetic energy Molecules that have the same temperature have the same average kinetic energy He SO 2 For 2 containers with 2 different gases at the same temperature. K.E. He = K.E. SO 2 If they have the same kinetic energy, will they have the same velocity? Diffusion, Effusion and Graham’s Law INCLUDE PICTURE " http://t1.gst atic.com/im ages?q=tbn :8FShhX1G LiEDtM:http ://upload.wi kimedia.org /wikipedia/c ommons/ar chive/9/93/ 200702081 92623!Sulf ur-dioxide- 3D-vdW.pn g" \* MERG EFORMATI NET INCLUDE PICTURE " http://t1.gst atic.com/im ages?q=tbn :8FShhX1G LiEDtM:http ://upload.wi kimedia.org /wikipedia/c ommons/ar
Diffusion and effusion are important gas behaviours explained by KMT. 1) Diffusion: rate at which a gas travels across a certain space as it moves from high to low concentration. ex. Perfume, axe, ammonia 2) Effusion: rate at which gas escapes from small hole in a container. Graham’s Law Observation: Lighter gases effuse faster than heavier gases. Law: The rate of effusion or diffusion is inversely proportional to the square root of its molar mass. Rate gas = 1___ √MM gas The relative rates of 2 gases that effuse or diffuse is shown in Graham’s Law: Where does this equation come from? (Derivation of Formula) Well, Graham’s law is based on the observation that the average kinetic energy (K.E.) of any two gas samples at the same temperature are equal. For gas sample 1: For gas sample 2: K.E. = (1/2)m 1 v 1 2 K.E. = (1/2)m 2 v 2 2 Since the K.E. is equal, (1/2)m 1 v 1 2 = (1/2)m 2 v 2 2 Cancel ½ since it is on both sides, m 1 v 1 2 = m 2 v 2 2 The equation can be arranged to show the relationship between the ratio of the masses and velocities. v 1 2 = m 2 v 2 2 m 1 Take the square root of both sides, v 1 2 = m 2 v 2 2 m 1 This gives, v 1 = √m 2 v 2 √m 1 Since molar mass is proportional to mass, we can replace mass in the formula. Example 1: If I pop a balloon of methane and a balloon of carbon dioxide at the same time which gas will diffuse to the other end of the room more quickly? 200702081 92623!Sulf ur-dioxide- 3D-vdW.pn g" \* MERG EFORMATI NET INCLUDE PICTURE " http://t1.gst atic.com/im ages?q=tbn :8FShhX1G LiEDtM:http ://upload.wi kimedia.org /wikipedia/c ommons/ar chive/9/93/ 200702081 92623!Sulf ur-dioxide- 3D-vdW.pn g" \* MERG EFORMATI NET Rate 1 = √ MM 2 Rate 2 √ MM 1 Rate 1 = √ MM 2 Rate 2 √ MM 1 Note: velocity is a rate
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
  • Access to all documents
  • Unlimited textbook solutions
  • 24/7 expert homework help
Rate CH 4 = √ 44.01 g/mol = 1.66 Methane will diffuse 1.66 times faster. Rate CO 2 √ 16.05 g/mol Example 2: The rate of diffusion of an unknown gas is four times faster than oxygen gas. Calculate the molar mass of the unknown gas. Rate 1 = 4.00 Rate 2 The molar mass of oxygen is 32 g/mol. Substitution into Graham’s equation gives 4.00 = √32 g/mol √MM 1 Squaring both sides of the equation yields 16.00 = 32 g/mol MM 1 Molar mass of gas 1 = 32 g/mol 16 Molar mass of gas 1 = 2 g/mol Thus, the gas is hydrogen. Factors Affecting Effusion and Diffusion 1) Temperature: At a lower temperature the kinetic energy of a gas is lower, so it moves slower (diffusion is slower). 2) Size of the Particles: As size increases velocity of a gas decreases. 3) Medium: Diffusion and effusion is affected by the substance into which it diffuses/effuses. ex. a gas diffuses slower into a liquid or gel then into another gas. Definitions Kinetic energy: Energy of motion
Temperature: A measure of the average kinetic energy of the particles The units for temperature are degrees Celsius (°C) or Kelvin (K). The origin on the Kelvin scale is called Absolute Zero , it is the temperature where the particles are at the lowest possible energy. To Convert: Temperature (K) = °C + 273K Pressure: A measure of the amount of force exerted on a given area The units for pressure are – atmospheres (atm) – mm of mercury (mm Hg) – kilopascals (kPa) – Torr, Bar, PSi (pounds/sq in) Standard Temperature and Pressure (STP): Set of conditions where T = 273K and P = 1 atm or 101.3 kPa Standard Ambient Temperature and Pressure (SATP): T = 298K and P=1 atm or 101.3 kPa Volume: amount of space an object occupies. The unit for volume = *L* Remember: 1 mL = 1 cm 3 1 cc = 1 cm 3 How to Measure Pressure Barometer A barometer measures atmospheric pressure by balance the weight of mercury in a glass tube against the weight of air in the atmosphere. Manometer
Converting between Units of Pressure: atm., mmHg/torrs and kPa There are three different units of pressure used in chemistry. This is an unfortunate situation, but we cannot change it. You must be able to use all three. Here they are: 1. atmospheres (symbol = atm) 2. millimeters of mercury (symbol = mm Hg), torr is another name for mm of Hg 3. Pascals (symbol = Pa) or, more commonly, kiloPascals (symbol = kPa) Standard Conditions 0.00 °C = 273 K 1.00 atm = 760.0 mm Hg = 101.3 kPa Doing Pressure Conversions I. Between atmospheres and millimeters of mercury : 1.00 atm = 760.0 mmHg Example #1: Convert 0.875 atm to mmHg. Solution: multiply the atm value by 760.0 mmHg / 1 atm. **Notice that the atm values cancel, leaving mmHg.** Example #2: Convert 745.0 mmHg to atm. 0.875 atm x 760.0 mmHg = 665 mmHg 1 atm
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
  • Access to all documents
  • Unlimited textbook solutions
  • 24/7 expert homework help
Solution: multiply the mmHg value by 1 atm/760.0 mmHg **Notice that the mmHg values cancel, leaving atm.** II. Between atmospheres and kilopascals: 1.00 atm = 101.3 kPa Example #3: Convert 0.955 atm to kPa. Solution: multiply the atm value by 101.3 kPa / 1 atm. **Notice that the atm values cancel, leaving kPa.** Example #4 : - Convert 98.35 kPa to atm. Solution : multiply the kPa value by 1 atm/101.3 kPa. **Notice that the kPa values cancel, leaving atm.** III. Between millimeters of mercury and kilopascals : 760.0 mmHg = 101.3 kPa Example #5 : Convert 740.0 mmHg to kPa. Solution: multiply the mmHg value by 101.3 kPa/760 mmHg **Notice that the mmHg will cancel, leaving kPa.** Example #6: Convert 99.25 kPa to mmHg. Solution: multiply the kPa value by 760.0 mmHg/101.3 kPa **Notice that the kPa will cancel, leaving mmHg ** THE GAS LAWS 745.0 mmHg x 1 atm = 0.9802 atm 760.0 mmHg 0.955 atm x 101.3 kPa = 96.74 kPa 1 atm 98.35 kPa x 1 atm = 0.97 atm 101.3 kPa 740.0 mmHg x 101.3 kPa = 98.63 kPa 760.0 mmHg 99.25 kPa x 760.0 mmHg = 744.6 mmHg 101.3 kPa
B oyle’s Law: When temperature (T) and moles (n) are constant, the volume of a gas is inversely proportional to its pressure. Where k is a constant, not to be confused with Kelvin (K). Pressure vs. Volume Pressure (kPa) Volume (cm 3 ) P x V (kPa x cm 3 ) 66.7 107.5 158.6 222.3 50 31 21 15 3335.0 3332.5 3330.6 3334.5 Avg constant: 3333.15 kPa k = P x V P = k V Inverse
P = 3333.15 V The product of the variables (P x V) is a constant (k). Gay – Lussacs Law: When volume (V) and moles (n) are constant we observe the following relationships. There is a direct relationship between T(K) and P. There is a partial relationship between T(°C) and P. For temperature in Kelvin (direct relationship): Where k is a constant, not to be confused with Kelvin (K). k = P/T The quotient of P/T is a constant. P = kT
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
  • Access to all documents
  • Unlimited textbook solutions
  • 24/7 expert homework help
Charles’ Law: When pressure (P) and moles (n) are constant we observe the following relationships. There is a direct relationship between T(K) and V. There is a partial relationship between T(°C) and V. For temperature in Kelvin (direct relationship): Where k is a constant, not to be confused with Kelvin (K). k = V/T The quotient of V/T is a constant. V = kT * At zero Kelvin it is assumed that the particles no longer move so they do not occupy space. * Furthermore, according to KMT, the volume of the particles is negligible (NO volume) P Direct Partial
Amedeo Avogadro’s Law When pressure (P) and temperature (T) are constant, the relationship between n and V is direct. For the temperature in Kelvin: Where k is a constant, not to be confused with Kelvin (K). Partial Direct Direct n V V = kn
Important Statement: If you have the same volume (or identical containers) of 2 gases they’ll have the same number of molecules (at constant T and P). Avogadro’s Law determined the MOLAR VOLUME of any gas, basically his theory states: ** Volume of 1 mol of a gas at STP = 22.4 L ** The Math Bit: Bring all the relationships together in one beautiful equation but first isolate k in each mathematical relationship. Boyle’s: k = PV G.L.’s : k = P T Charles’: k = V T Avogadro’s : k = V n R k = PV nT The k is now replaced with R, the universal gas constant. We can now rearrange the formula to give the Ideal Gas Law Equation : PV = nRT or the PerVneRT equation
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
  • Access to all documents
  • Unlimited textbook solutions
  • 24/7 expert homework help
To determine the universal gas constant (R) use standard conditions and the Ideal Gas Law: Pressure: 101.3 kPa Temperature: 273K Moles: 1 Volume: 22.4 L (*Remember Avogadro’s law*) R = PV nT R = (101.3 kPa)(22.4 L) (273 K)( 1 mol) R = 8.31 kPa ∙ L K ∙ mol To determine the Combined Gas Law where final or initial conditions of a gas can be calculated: Initial Final R = P 1 V 1 R = P 2 V 2 n 1 T 1 n 2 T 2 Since the universal gas constant is the same in both equations, we can set them equal to one another. General Gas Law P 1 V 1 = P 2 V 2 n 1 T 1 n 2 T 2 Because the formula is equal to a constant, it is possible to solve for a change in volume, temperature, or pressure using a proportion. ** Note: For temperature the proportional situation (direct relationship) is only occurs for the Kelvin scale, therefore when using this equation the temperature must be in Kelvin. ** We obtain the Combined gas law equation where the amount (moles) of gas does not change (cancels out). P 1 V 1 = P 2 V 2 n 1 T 1 n 2 T 2
Example: A weather balloon is filled with Helium, He, until the internal pressure reaches 95 kPa. The temperature of the gas is 25°C. The balloon rises to an altitude of 1800m where the pressure is 80 kPa and the temperature is 15°C. Under these conditions, how many times greater or smaller will the final volume be in comparison to its volume? Ideal vs Real Gases Ideal and Real gases both have the same behaviour according to the gas laws (same graphs, mathematical relationships) Ideal Gas -obeys all postulates of the KMT For ideal gases we assume 1) no attraction between gas molecules 2) volume of a gas is zero This works at high temperature and low pressure. Real Gas Do not obey postulates of KMT, especially:
- postulate stating gases are in constant random motion - negligible attractive/repulsive forces - particles volume is negligible So, gases no longer behave ideally (become real gases) under the following conditions. 1) High Pressure 2) Low Temperature To be considered an ideal gas, the constant R = 8.31 kPa ∙ L K ∙ mol To show a gas is ideal you must calculate R. Dalton’s Law of Partial Pressures At constant volume and temperature, the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures. P total = P 1 + P 2 + P 3 Partial pressure: Contribution each gas in a mixture makes to the total gas pressure. **The proportionate pressure exerted by each gas in a mixture does not change as the temperature, pressure or volume changes.** Dalton found that since each gas particle behaves independently of other gases (KMT – no attraction or repulsion between particles) each gas in a mixture contributes to the total pressure based on its percentage of the mixture. A manometer cannot measure the partial pressure of a gas it can only measure the total pressure. Therefore, we need to use the molar proportion to determine the partial pressure of each gas. To find the partial pressure of a gas P A = n A ∙ P T n T where P A = Partial pressure of gas A, expressed in kilopascals (kPa) or millimeters of mercury (mm Hg) n A = Quantity of gas A, expressed in moles (mol) n T = Total quantity of gas, expressed in moles (mol)
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
  • Access to all documents
  • Unlimited textbook solutions
  • 24/7 expert homework help
P T = Total pressure of the mixture, expressed in kilopascals (kPa) or millimeters of mercury (mm Hg) Gas Stoichiometry Example 1 Calcium carbonate decomposes at high temperature to form CO 2 and CaO. How many grams of CaCO 3 will I need to form 3.45 L of CO 2 ? This reaction occurs at 110°C and 1 atm. CaCO 3 (s) CO 2 (g) + CaO (s)
Example 2 1.25 L of ethylene gas is combusted at a temperature of 398 K and a pressure of 101.3 kPa, what mass of water is produced? C 2 H 4 (g) + 3 O 2 (g) 2 CO 2 (g) + 2 H 2 O (g)