Calculate Cp of a Gas at STP - 4.48 L & 15°C

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Discussion Overview

The discussion revolves around calculating the specific heat capacity at constant pressure (Cp) of an ideal gas given its volume, temperature change, and the energy required to raise the temperature at constant volume. The context includes theoretical considerations and relationships between heat capacities.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Participants discuss the relationship between internal energy change and heat capacities, specifically using the equation ΔU = nCvΔT to find Cv.
  • Some participants express uncertainty about how to derive Cp from Cv, particularly since the process is at constant volume.
  • There is mention of a relationship between Cv and Cp, specifically Cp - Cv = R, but the applicability is questioned due to the unknown nature of the gas and its degrees of freedom.
  • One participant notes that the calculation of Cv yields a non-integer result, which complicates finding an integral value for Cp.
  • Participants inquire about the value of R in calorie units and its relevance to the calculations.

Areas of Agreement / Disagreement

Participants generally agree on the relationships between Cv, Cp, and R, but there is disagreement regarding the applicability of these relationships due to the unknown properties of the gas and the resulting calculations. The discussion remains unresolved regarding the final calculation of Cp.

Contextual Notes

The discussion highlights limitations related to the assumptions about the gas's nature and degrees of freedom, which are not specified in the problem statement. This uncertainty affects the ability to definitively calculate Cp.

utkarshakash
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Homework Statement


4.48 L of an ideal gas at STP requires 12 cal to raise the temperature by 15°C at constant volume. The Cp of the gas is (in cal)?


The Attempt at a Solution



ΔU = nCvΔT
I can find out C_v from above equation but how to get C_p? I assume it would be wrong to use this equation ΔQ=nCpΔT as the process is carried out at constant volume and not pressure.
 
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utkarshakash said:

Homework Statement


4.48 L of an ideal gas at STP requires 12 cal to raise the temperature by 15°C at constant volume. The Cp of the gas is (in cal)?


The Attempt at a Solution



ΔU = nCvΔT
I can find out C_v from above equation but how to get C_p? I assume it would be wrong to use this equation ΔQ=nCpΔT as the process is carried out at constant volume and not pressure.

You said you can calculate ##C_v## (and btw, it comes out to be a nice integer, keep everything in cal). Do you know of a relation between ##C_v## and ##C_p##?
 
Pranav-Arora said:
You said you can calculate ##C_v## (and btw, it comes out to be a nice integer, keep everything in cal). Do you know of a relation between ##C_v## and ##C_p##?

I did use that relation earlier but since the question is an integer type(you know what they mean,don't you?) it won't give me an integral answer(rounding off the digits still gives an answer beyond the range ).
 
utkarshakash said:
I did use that relation earlier but since the question is an integer type(you know what they mean,don't you?) it won't give me an integral answer(rounding off the digits still gives an answer beyond the range ).

May I know which relation did you use?

I should have said to use a relation between ##C_v## and degrees of freedom. You should be able to calculate ##C_p## once you have the degrees of freedom.
 
Pranav-Arora said:
May I know which relation did you use?

I should have said to use a relation between ##C_v## and degrees of freedom. You should be able to calculate ##C_p## once you have the degrees of freedom.

Cp-Cv = R

The question does not state the nature of gas. So degrees of freedom is not known.
 
utkarshakash said:
Cp-Cv = R

So what did you plug in for Cv? Note that it should be in cal. And what is the value of R in calorie units?
 
R = 1.9872041 cal/K/mole
and Cv you can calculate from ΔU = nCvΔT.
the put Cp-Cv = R
 

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