Flask A is CH_4, 1.0 L, 2.0 atm, 100 degree C. Flask B is H_2, 2.0 L, 4.0 atm.,

Question

Flask A is CH_4, 1.0 L, 2.0 atm, 100 degree C. Flask B is H_2, 2.0 L, 4.0 atm., 100 degree C. Flask C is He, 2.0 L, 2.0 atm, 100 degree C. Which has the fastest molecules? A. B. C. All are the same. Same flasks as above. Which has the greatest density? A. B. C. All are the same. Same flasks as above. Which has the greatest mass? A. B. C. All are the same. Same flasks as above. Which has the greatest number of molecules? A. B. C. All are the same. Same flasks as above. Which has the greatest kinetic energy? A. B. C. All are the same.

Explanation / Answer

Hi,

moles of CH4 in flask A (na)= PV/RT= 2*1/0.08205*373= 0.065 gmoles

moles of H2 in flask A (nb)= PV/RT= 4*2/0.08205*373= 0.261 gmoles

moles of He in flask A (nc)= PV/RT= 2*2/0.08205*373= 0.131 gmoles

Which has the fastet molecule?

we know R.M.S= (3nRT/M)1/2

let Va, Vb and Vc be the rms velocity of molecules in flask A, B and C respectively,

then, Va:Vb:Vc= (3naRT/Ma)1/2 :(3nbRT/Mb)1/2 :(3ncRT/Mc)1/2

=(na/Ma)1/2 :(nb/Mb)1/2 :(nc/Mc)1/2

= 0.064: 0.722: 0.512

= 1: 11.28: 8

hence, H2 has tha fastest molecule. ans: (B)

Which has the greatrest density?

density= number of molecules in flask/ Volume of flask,

let, da, db and dc be the densities of flask A, B and C, va, vb and vc be the volumes of flask A, B and C

da: db: dc= (na*Ma/va):(nb*Mb/vb): (nc*Mc/vc)= (0.065*16/1):(0.261*2/2): (0.131*2/2)= 1.04: 0.261: 0.131= 7.94: 2.00:1

hence, flask A has the greatest density. Ans: (A)

Which has the greatest mass?

let ma, mb and mc be the mass of flask A, B and C,

ma: mb: mc= (na*Ma):(nb*Mb): (nc*Mc)= (0.065*16):(0.261*2): (0.131*2)= 1.04: 0.522: 0.262

clearly, flask A has the greatest mass. ans: (A)

which has the greatest number of molecules?

The one with the greatest moles has the greatest number of molecules.

hence, ans: (B), H2 has the greatest number of molecules.

Thank you

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