ideal gas law why bother with gases? properties of a gas animation p, v, t, n ideal gas law examples...
Post on 29-Dec-2015
259 Views
Preview:
TRANSCRIPT
Ideal Gas Law
• Why bother with Gases?• Properties of a Gas• Animation P, V, T, n• Ideal Gas Law• Examples of Ideal Gas Law• Ideal Gas Law - #molecules version
Temperature and Gases• Gas
– Simplest material phase – all kinetic energy.– Energy “reservoir” – convert disordered KE to useful mechanical
work.
• Properties of a Gas– Pressure– Volume– Temperature– Quantity
• 4 Properties are interrelated – Animation– Ideal gas law
Ideal Gas Animation• Gas/piston animation
(Java animation) ……..……
• Gas/piston animationhttp://www.chem.ufl.edu/~itl/2045/MH_sims/ideal_nav.swf
• Other animationshttp://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/gam2s2_6.swf
idealgas.jnlp
ideal_nav.swf
gam2s2_6.swf idealGasModel.swf
Ideal Gas Observations• Observations of P, V, T, n
– Pressure vs. Volume (Boyle’s Law) P proportional to 1/V– Volume vs. Temperature (Charle’s law) V proportional to T– Pressure vs. Temperature (Gay-Lussac’s Law) P proportional to T– Pressure and volume vs. quantity PV proportional to n
Ideal Gas Law – Primary units• Ideal gas law combines Boyle’s, Charles, Gay-Lussac’s
PV = nRT
– P proportional 1/V– V proportional T– P proportional T
– P proportional n
• Units – P in pascals – V in m3 – T in K° (not C °)– n in moles– R = 8.314 J/mol-K
• Definition of Mole n = mass/molecular mass (N2=28g/mol, O2= 32g/mol, etc.)
Ideal Gas Law – Alternative units• Ideal gas law combines Boyle’s, Charles, Gay-Lussac’s
PV = nRT – P in atmospheres– V in liters– T in K° – n in moles– R = .0821 L-atm/mol-K
• Use either primary units or alternative units completely, don’t mix n’ match!
• Use primary units for First Law (Ch 15) calculations.
Celsius vs. Kelvin• Degree sizes same!
• Kelvin = Celsius with zero shifted to absolute zero.
• May use Celsius when only relative changes important.– Thermal Expansion
– Specific and Latent Heat problems
– Thermal Conduction
• Must use Kelvin when absolute temperature important.
– Ideal Gas Law
– Kinetic Theory
– Thermal Radiation
– First and Second Law Thermodynamics
Similar to Gauge vs. Absolute Pressure
Example 13-10 - volume 1 mole at STP
• STP = 0C (273K), 1 atm (101.3 kPa)
• Primary units
• Alternative units
Example 13-11 - helium balloon
• Volume of 18 cm radius sphere
• Number of moles in alternative units (just being different)
• Mass of Helium
Example 13-12 - mass of air in room
• Volume of 5 x 3 x 2.5 m room
• Number of moles
• Mass of Air @ 29 g/mol (N2 28 g/mol, O2 32 g/mol)
Example 13-13 – automobile tireAn automobile tire is filled to a gauge pressure of 200 kPa at 10°C. After a long drive the temperature as risen to 40°. What is the pressure now?
• Strategy – Put all constant quantities on same side of Ideal Gas Law
• Convert 200 kPa gauge pressure to 301 kPa absolute pressure
• Solve
Convert 333 kPa absolute pressure back to 232 kPa gauge pressure
More examples of ideal gas
• Problem 29 V2 = V1 (P1/P2) (T2/T1)
• Problem 30 T2 = T1 (P2/P1) (V2/V1)• Problem 31 ρ = 32 x 10-3/22.4 x 10-3
• Problem 32 P2 = P1 (n2/n1)• Problem 33• Problem 36 n2 = n1 (P2/P1)
• Problem 39 P2 = P1 (V1/V2)(T2/T1)
Problem 29 – V change with P, T
• First move all constant quantities to one side
• Then solve for V2
Note: Arbitrary units OK, since only ratios important
Problem 30 – T change with P, V
• Move all constant quantities to one side
• Solve for T2
(Diesel car) Note: Arbitrary units OK, since only ratios important
Problem 31 – Density of O2
• Volume of 1 mole at STP22.4 L = 0.0224 m3 (shown earlier)
• Mass of a mole O2
32 g = .032 kg (lookup in table)
• Density
Problem 32 – Gas substitution
• Calculate mole ratio for equal mass CO2 and N2
(since mass equal)
• Move all constant quantities to one side
• Solve for P2
Problem 36 – Gas substitution
• First find #moles O2
• Move all constant quantities to one side
• Solve for n2
670 moles
• Then find mass 670 moles Helium
Problem 39 – P change with V, T
• Move all constant quantities to one side
• Solve for V2
Note: Arbitrary units OK, since only ratios important
top related