Question

A gas expands isothermally against constant external pressure of 1 atm from a volume of 10 dm3 to a volume of 20 dm3.In the process, it absorbs 800 J of thermal energy from surroundings. What will be the value of internal energy change?

Answer 1

The value of internal energy change is -213 J.

Explanation:

Given the pressure, P = 1 atm.

The initial volume V =10 dm^3.

The final volume, v = 20 dm^3.

The heat absorbs from surroundings, Q = 800 J.

Now to calculate the change in internal energy use first law of thermodynamics,

$\Delta U=Q+\Delta W$

We know,

$\Delta W=-P(v -V)$

Substitute the given values, we get

$\Delta W=-1atm(20dm^3-10dm^3)$

$\Delta W=-10dm^3.atm$

In joule,

$\Delta W=-10dm^3.atm\times\frac{8.314J.mol/K}{0.08260dm^3atm.mol/K}$

       =-1013 J.

Therefore, change in internal energy

$\Delta U=800J+(-1013J) =-213J.$

Thus, the value of internal energy change is -213 J.

#Learn More: Law of thermodynamics.

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