Examle roblems Chater : he Kinetic heory o Gases Homework:, 8,,, 5, 7 (. 5-5)
9. An automobile tire has a volume o.64 x m and contains air at a gauge ressure (above atmosheric ressure) o 65 kpa when the temerature is. C. What is the gauge ressure o the air in the tires when its temerature rises to 7. C and its volume increases to.67 x m? Assume atmosheric ressure is.x 5 Pa. At state i: i i nr nr i At the inal state : nr ii i Gauge ressure: - G o
. A samle o an ideal gas is taken through the cyclic rocess abca shown in the igure below; at oint a, K. (a) How many moles o gas are in the samle? What are (b) the temerature o the gas at oint b, (c) the temerature o the gas at oint c, and (d) the net energy added to the gas as heat during the cycle? (a) Alying the equation o state: nr n R At oint a,.5 kn/m or 5 N/m ; m. 5 n.5 (mol) 8. aa bb nr nr. (b) 5 a At oint b, 7.5 kn/m or 75 N/m ; m. b b nr b b 75.5 8 (K)
(c) see art b; c 6 K; (d) Alying the irst law o thermodynamics: E Q W W: work done by the system. For a closed cycle, E: Q W W ( )( ) b c b a W 5. 5 (J)
4. In the temerature range K to K, the ressure o a certain nonideal gas is related to volume and temerature by: ( 4.9 J / K) (.66 J / K ) How much work is done by the gas i its temerature is raised rom 5 K to K while the ressure is held constant? Work done by the gas is comuted by the ollowing ormula: W W i i d 4.9( ( i ) ).66( i i ) K; 5K W i (J)
8. he temerature and ressure in the Sun s atmoshere are.x 6 K and. Pa. Calculate the rms seed o ree electrons (mass 9.x - kg) there, assuming they are an ideal gas. v rms R M R mn A v rms 6 8. 9. 6. 9.5 6 (m/s)
. Calculate the rms seed o helium atoms at K, the molar mass o helium atoms is 4.6 g/mol. v rms 8..5 4.6 R M (m/s)
4. At 7 K and. x - atm, the density o a gas is.4 x -5 g/cm. (a) Find v rms or the gas molecules. (b) Find the molar mass o the gas and (c) identiy the gas (hint: see able 9-). (a) Root-mean-square seed: () and (): M gas v rms R M nm ρ M nr v rms ρ () ρ n ρ () ρ.4 5 g/cm.4 kg/m. atm v rms. 494 m/s Pa
(b) Equation o state: M ρ n nr () () M ρ n ρr (c) M.8 kg/mol 8 g/mol From able 9., the gas is nitrogen (N )
5. Determine the average value o the translational kinetic energy o the molecules o an ideal gas at (a). C and (b) C. What is the translational kinetic energy er mole o an ideal gas at (c). C and (d) C? (a) he translational kinetic energy er molecule: K k + 7 7 K : (b) see (a): K K.8.8 7 7 5.65 (c) he translational kinetic energy er mole: (d) K mole 5.65 K mole 6. 4.7 (J) 7.7.4 (J) (J) (J) K K mole N A
Note: I a samle o gas has n moles (or N molecules), its total translational kinetic energy is: K n K n N total mole A K K total n K mole n N A k nr K total nr
Homework: 8,,, 4 (age 5)
8. At what requency would the wavelength o sound in air be equal to the mean ree ath o oxygen molecules at. atm ressure and. C? take the diameter o an oxygen molecule to be. x -8 cm. Mean Free Path: λ MFP k.8 J/K; 7 K; d Frequency o sound in air: v sound in air cm 4 m/s 8 : λ MFP m sound k πd. λ sound 5 Pa; vsoundin air 9. 8 m v soundin air λ MFP 4 9.68 8 9. sound (Hz) or.68 GHz
. At C and 75 torr ressure, the mean ree aths or argon gas (Ar) and nitrogen (N ) are λ Ar 9.9x -6 cm and λ N 7.5x -6 cm. (a) Find the ratio o the diameter o an Ar atom to that o an N molecule. What is the mean ree ath o Ar at (b) C and 5 torr, and (c) -4 C and 75 torr? Mean Free Path: (a) he ratio d Ar to d N : (b): λ k πd d λ Ar N d λ N Ar k k λ ; λ πd πd λ λ
. he seeds o molecules are.,., 4.,..., km/s. What are their (a) average seed and (b) rms seed? (a) v N + + 4 +... + 65 i i N v 6.5 (km/s) ( ) i (b) 7.(km/s) v rms v avg N N v i
4. wo containers are at the same temerature. he irst contains gas with ressure, molecular mass m, and rms seed v rms. he second contains gas with ressure.5, molecular mass m, and average seed v avg.v rms. Find the mass ratio m /m. RMS seed: v rms R m Average seed: v 8R πm
Homework: 4, 44, 46, 54, 56, 78 (. 5-55)
4. What is the internal energy o. mol o an ideal monatomic gas at 7 K? E nc C R.5 J mol - K - E..5 7 685 (J) E 6.8 (kj)
44. One mole o an ideal diatomic gas goes rom a to c along the diagonal ath in Fig. 9-5. he scale o the vertical axis is set by ab 5. kpa and c. kpa, and the scale o the horizontal axis is set by bc 4. m and a. m. During the transition, (a) what is the change in internal energy o the gas, (b) how much energy is added to the gas as heat? (c) How much heat is required i the gas goes rom a to c along the indirect ath abc? a) 5 Eint nc nr 5 ( Pc c P a a ) 5J b) Q E W 5 7 J int + + c) Q E + int W ac
46. Under constant ressure, the temerature o. mol o an ideal monatomic gas is raised 5. K. What are (a) the work W done by the gas, (b) the energy transerred as heat Q, (c) the change E int o the gas, and (d) the change K in the average KE er atom? (a) At constant ressure: W nr. 8. 5. 74 (J) (b) Q E int 5 5 nc n R W (c) We use the irst law o thermodynamics: (d) For a monatomic gas: K avg Q W Eint 95 74 K 95 (J) (or Eint nc nr ) k 56 (J) K avg avg.8 5.. k (J)
54. We know that or an adiabatic rocess. Evaluate constant or an adiabatic rocess involving exactly. mol o an ideal gas assing through the state having exactly.5 atm and K. Assume a diatomic gas whose molecules rotate but do not oscillate. Equation o state: nr atm C C For a diatomic gas, 5: constant.5.. 5 nr (Pa) constant. 8.. (m ) 5.5. C + C 5 R 7 5. 7 5 constant.8 R + R R.8 (N m. ) (N/m (m ).4 )
56. Suose.L o a gas with., initially at 85 K and. atm, is suddenly comressed adiabatically to hal its initial volume. Find its inal (a) ressure and (b) temerature. (c) I the gas is then cooled to 7 K at constant ressure, what is its inal volume? ; i i i i i i i nr ' ' constant,
78. (a) An ideal gas initially at ressure undergoes a ree exansion until its volume is. times its initial volume. What then is the ratio o its ressure to? (b) he gas is next slowly and adiabatically comressed back to its original volume. he ressure ater comression is (.) /. Is the gas monatomic, diatomic, or olyatomic? (c) What is the ratio o the average kinetic energy er molecule in this inal state to that in the initial state? (a) ; (b) ' ' C R C C C 4 + + + olyatomic 6 :
(c) K avg k ' ' K K r avg avg ).44 (since ' ' ' ' / ' r