Need help with this 5.90 g of nitrogen gas at 22.0 degree C and an initial press

Question

Need help with this

5.90 g of nitrogen gas at 22.0 degree C and an initial pressure of 2.10 atm undergo an isobaric expansion until the volume has tripled. How much heat energy is transferred to the gas to cause this expansion? Express your answer with the appropriate units. The gas pressure is then decreased at constant volume until the original temperature is reached. What is the gas pressure after the decrease? Express your answer with the appropriate units. What amount of heat energy is transferred from the gas as its pressure decreases? Express your answer with the appropriate units.

Explanation / Answer

A)
Ti =22 oC = (22+273) K = 295 K
Since volume is tripled, T should also triple.
So Tf= 3* Ti = 3* 295 = 885 K

number of moles of N2 = mass / molar mass = 5.9 / 28 = 0.2107 mol

use:
for N2,
CV = 29 J/molK
Q = n*Cp*(Tf-Ti)
= 0.2107 *29 * (885- 295)
=3605.1 J
Answer : 3605.1 J

B)
Pi= 2.1 atm
Pf = ?
Given Ti = 885 K
Tf = 295 K
use:
Pf/Pi =Tf/Ti
Pf/2.1 = 295/885
Pf = 0.7 atm
Answer: 0.7 atm

C)
Cv forN2 = 20.7 J/molK
As volume is constant W= 0
Q= n*Cv*(Tf-Ti)
= 0.2107 *20.7*(295-885)
= -2573.3 J
Answer: 2573.3 J

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