Solving Part B of PV=NkbT: An Explanation

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In summary, the conversation discusses a problem involving finding the number of atoms in a given volume and calculating the change in entropy using the Boltzmann Constant and Macrostate. The first part involves finding the number of atoms using given values for pressure, volume, and temperature. The second part raises a problem with calculating the change in entropy due to a very small value for V^N, leading to an undefined result for In(0). The conversation suggests simplifying the equation or checking for errors in the relationship between change in entropy and Macrostate.
  • #1
Junkwisch
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Homework Statement



"see attachment"

Homework Equations



PV=NkbT
Change in entropy = Boltzmann Constant x In(Macrostate)

The Attempt at a Solution



for part A, I knew that PV=NKbT

giving that pressure is 101300Pa volume is 1*10^-3 m^3, Kb is 1.38*10^-23 and T=300K
I find N to be 2.446*10^22 atoms


the problem I have is with part B

the question states that microstate is proportion to V^N where N is the number of atom I found in part A, and V is the volume which is 1*10-9 m^3. Thus V^N is a very small number which is pretty much zero. Change in entropy = Boltzmann Constant x In(Macrostate), since Macrostate is zero, there is an error in this calculation. Since In(0) is undefined. What am I suppose to do in this question??
 
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  • #2
I forgot to attach the question, here it is
 

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  • #3
Hi Junkwisch!

Always in physics things are only big or small relative to other things. The numerical value of [itex]V^N[/itex] depends entirely on what units you're using.

Perhaps you can simplify [itex]\ln\left(V^N\right)[/itex] without making an approximation? :smile:
 
  • #4
Junkwisch said:
Change in entropy = Boltzmann Constant x In(Macrostate)
You should check that you have the correct relationship here. How can the left side of the equation be a change when there's no corresponding change present on the righthand side of the equation? Also, what is "Macrostate" supposed to represent?
 
  • #5


As a scientist, it is important to recognize when a calculation may lead to an undefined or nonsensical result. In this case, the calculation for change in entropy is not applicable because the macrostate is zero, which is not a physically meaningful value. This could be due to the extremely small volume used in the calculation, which makes the macrostate approach zero.

To address this issue, I would suggest using a larger volume for the calculation, or considering a different approach altogether. Additionally, it is important to remember that these equations and calculations are simplifications of complex systems, and may not always accurately represent real-world situations. It is important to critically evaluate the results and consider any potential limitations or errors in the calculations.
 

1. How do you solve Part B of PV=NkbT?

To solve Part B of PV=NkbT, you need to use the ideal gas law equation, which is PV=NkbT. This equation relates the pressure (P), volume (V), number of moles (N), Boltzmann constant (kb), and temperature (T) of an ideal gas. To solve for any of these variables, you need to rearrange the equation and plug in the known values.

2. What is the purpose of solving Part B of PV=NkbT?

The purpose of solving Part B of PV=NkbT is to determine the value of one of the variables (P, V, N, kb, or T) when the rest are known. This equation is commonly used in thermodynamics and is important in understanding the behavior of gases.

3. What is the ideal gas law equation?

The ideal gas law equation, PV=NkbT, is a mathematical relationship between the pressure, volume, number of moles, Boltzmann constant, and temperature of an ideal gas. It is based on the assumptions that the gas particles have negligible volume and that there are no intermolecular forces between them.

4. How do you rearrange the ideal gas law equation?

To rearrange the ideal gas law equation, you can use algebraic manipulation to isolate the variable you want to solve for. For example, if you want to solve for pressure (P), you would rearrange the equation to P= NkbT/V. Make sure to keep track of units and convert them as needed.

5. What are the units for each variable in the ideal gas law equation?

The units for each variable in the ideal gas law equation are as follows: pressure (P) is measured in Pascals (Pa), volume (V) is measured in cubic meters (m^3), number of moles (N) is measured in moles (mol), Boltzmann constant (kb) is measured in Joules per Kelvin (J/K), and temperature (T) is measured in Kelvin (K).

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