Thermodynamics and Internal Energy of a gas

In summary, the internal energy of a gas is initially 597 joules. After being compressed adiabatically with a pressure of 3.43 atm and a decrease in volume of 129 cm3, the internal energy of the gas becomes 448872 joules. However, there may be a mistake in the calculation as the final internal energy seems to be of a much larger magnitude.
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castrodisastro
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Homework Statement


The internal energy of a gas is 597 joules. The gas is compressed adiabatically and its volume decreases by 129 cm3. If the pressure applied on the gas during compression is 3.43 atm, what is the internal energy of the gas after adiabatic compression?


Homework Equations


First law of thermodynamics: ΔEinternal=Q-W
W=∫VfVi P dV

The Attempt at a Solution


I first converted 3.43 atm to Pascals. This gave me 3.475*105 Pascals.
I converted 129 cm3 to meters. This gave me 1.29 meters.

Since I need to use the first law of thermodynamics. I will need to know the work done to the system. I calculated this by taking the integral of 3.475*105 from 0m3 to 1.29m3 (since we were only given the change in volume I used 0m3 as my initial volume). My answer was 448275 Pa*m3 = 448275 Joules.

Rewriting the first law of thermodynamics as
Einternal,final-Einternal,initial=Q-W
I can rearrange to solve for Einternal,final. Since no heat is lost in an adiabatic process, Q=0.

So now we have

Einternal,final = Einternal,initial - W
Einternal,final = 597 J - (-448275 J)
Einternal,final = 448872 J

The reason I am confused is because the magnitude of the internal energy seems way too high. my answer could be correct but the reason I am suspiscious is because when I look at example problems done by other people, they convert atm to Pascals the same way I did, and when they calculate the work, the amount is of the same magnitude as I calculated (105), but when they add that work to their Einternal,initial, their amount of work in joules magically reduces to a value of magnitude 103. I say magically because they provide no explanation for this decrease. At first I thought maybe the conversion was from atm to kPa but the textbook, and online sources, state 1.0 atm to be equal to 101,325 Pascals. So is my answer correct or am I forgetting a step before I subtract the work from the Einternal,initial? I made sure to account for all units and my answer came out to Joules as they should but I am just concerned that I may not be decreasing the order of magnitude if I am supposed to. Thanks in advance.
 
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  • #2
1 cubic meter is 1000 liters, which is 1 million cubic centimeters. You ought to be adding about 44.8 J work.
(adiabatic process is NOT constant pressure; they probably gave the final pressure)
 
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  • #3
Ah ok. I see. Pretty simple mistake. Thanks
 

FAQ: Thermodynamics and Internal Energy of a gas

1. What is thermodynamics and internal energy of a gas?

Thermodynamics is the study of the relationship between heat and other forms of energy. Internal energy of a gas is the total energy of its microscopic particles, including their motion and interactions.

2. How is internal energy of a gas related to its temperature?

According to the kinetic theory of gases, the internal energy of a gas is directly proportional to its temperature. This means that as the temperature of the gas increases, so does its internal energy.

3. What is the first law of thermodynamics?

The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or converted from one form to another. This means that the internal energy of a gas can change due to heat transfer or work done on the gas.

4. How is the internal energy of a gas affected by changes in pressure and volume?

According to the ideal gas law, the internal energy of a gas is directly proportional to its temperature and the number of moles of gas. This means that changes in pressure and volume do not directly affect the internal energy of a gas, but they can indirectly affect it by changing its temperature.

5. What is the difference between internal energy and enthalpy of a gas?

The internal energy of a gas refers to its total energy, while enthalpy takes into account the energy transferred as heat at constant pressure. In other words, enthalpy includes the energy required to overcome any external pressure on the gas, while internal energy does not.

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