Calculate the change in internal energy (δe) for a system that is giving off 25.0 kj of heat and is changing from 12.00 l to 6.00 l in volume at 1.50 atm pressure. (remember that 101.3 j = 1 l∙atm) 14) ______
a.+25.9 kj
b.-16.0 kj
c.-25.9 kj
d.-24.1 kj
e.937 kj

Respuesta :

Since the system itself is giving off heat, this is a reduction in the internal energy.

heat = - 25,000 J

 

Since work is being done on the system, therefore it is an additional energy to the system. Work is given as:

work = - P dV

work = - 1.50 atm (6 L – 12 L)

work = 9 L atm

Since it is given that 1 L atm is equivalent to 101.3 J, therefore the total energy added is:

energy due to work = 9 L atm (101.3 J / 1 L atm)

energy due to work = 911.7 J

 

Therefore the total change in internal energy is the sum of heat and energy due to work:

Change in internal energy = - 25,000 J + 911.7 J

Change in internal energy = - 24,088.3 J

 

Therefore, approximately 24.1 kJ of energy is lost by the system in the total process.


Answer:

-24.1 kJ

The correct option is d. which is the change in internal energy is -24.9 kj.

Given to us:

  • Heat system is giving off, [tex]Q_{out}= -25000[/tex]
  • Initial volume, [tex]V_{i}=12\ l[/tex]
  • Final volume, [tex]V_{i}=6\ l[/tex]
  • Pressure, [tex]P= 1.50\ atm[/tex]
  • Also, a piece of additional information is given to us, [tex]101.3\ j = 1\ l\cdot atm[/tex].


Work

As work is being done on the system, meaning additional energy is provided to the system. Therefore,

[tex]\begin{aligned}W&=- \int\limits {P} \, dv\\&=-P\ dv\\\\&=-P\ (V_f-V_i)\\&=- (1.50) (6-12)\\&= 9\ l\cdot atm\end{aligned}[/tex]

Also,

[tex]1\ l\cdot atm=101.3\ j\\9\ l\cdot atm=101.3\times 9\\9\ l\cdot atm=911.7\ j[/tex]

According to the First law of thermodynamics,

[tex]\Delta U = Q - W\Delta\\\\where,\\ U = change\ in\ internal\ energy\\Q = heat\ added\\W = work\ done\ by\ the\ system[/tex]

Substituting the values,

[tex]\begin{aligned}\\\Delta U&= Q - W\Delta\\&= -25000+911.7\\&=-24,088.3\ j\\&= -24.0883\ kj\end{aligned}[/tex]

Hence, the change in internal energy is -24.0883 kj.

Learn more about  First law of thermodynamics:

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