DuckieDai Clausius-Clapeyron Equation Python Program

chemistry · MIT License

Overview

Use the integrated Clausius-Clapeyron relation to solve either pressure, either temperature, or enthalpy of vaporization.

Not calculator tested
Downloaded 34 times
Version 1.0.0
2167 bytes
Uses math

Download ccEQ.py Read the source How to install

Before you run it

TI-84 Plus CE Python · No calculator OS or Python App version has been verified.
TI Connect CE .py transfer is the intended path; calculator OS, Python App, transfer, and execution have not yet been tested for this release
Delta Hvap is constant over the temperature interval.
The vapor behaves ideally and liquid molar volume is negligible relative to vapor.
Pressures, temperatures, and supplied Delta Hvap must be positive; paired temperatures must differ when solving Delta Hvap.

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Follow the same opening, solve menu, prompts, validation, and result flow as the downloadable program.

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Learn the math

How the Clausius-Clapeyron equation works

The idea

A liquid's vapor pressure rises steeply as it warms. The Clausius-Clapeyron equation links the vapor pressures at two temperatures through the heat of vaporization.

It answers questions such as: what is the vapor pressure at a new temperature, or at what temperature will this liquid boil under a different pressure?

The formula

ln(P2/P1) = -(Hvap/R)*(1/T2 - 1/T1)

P1, P2: vapor pressures at the two temperatures, in the same unit
T1, T2: temperatures in kelvin
Hvap: heat of vaporization (kJ/mol)
R: 8.314 J/mol K, built in

Using the program

1 finds P2. 2 finds T2. 3 finds Hvap. 4 finds P1. 5 finds T1.
Enter the other four values when asked.

Worked example

Water boils at 373.15 K under 1 atm, and Hvap = 40.7 kJ/mol. To find its vapor pressure at 350 K, choose 1 and enter 1, 373.15, 350, and 40.7.

The program shows P2 = 0.4199 atm (it prints more decimal places), so water at 350 K has about 42% of normal atmospheric vapor pressure.

Tips and common mistakes

Temperatures must be in kelvin.
P2 comes out in the same unit you used for P1.
The equation assumes Hvap stays constant, so it is most accurate over a modest temperature range.

Where this comes up

It appears in the liquids and phase changes unit of general chemistry and again in physical chemistry, wherever vapor pressure, boiling point, and heat of vaporization are linked.

Exact reviewed bytes

Source code

Download .py

View source below, copy it when JavaScript is available, or download the exact .py bytes.

from math import log,exp

R=8.314

def duckiedai_intro(program_name,wait=True):
 title=program_name[:16]
 empty=16-len(title)
 left=empty//2
 right=empty-left
 print("+----------------------+")
 print("|   "+" "*left+title+" "*right+"   |")
 print("|                      |")
 print("|       __             |")
 print("|   ___(o )>  quack!   |")
 print("|   \\ <_. )           |")
 print("|    `---'             |")
 print("|     by DuckieDai     |")
 print("+----------------------+")
 print("Loading...")
 if wait:
  input("Press enter to start ")
  print("\n"*6)

def pos(s):
 while 1:
  try:
   x=float(input(s))
   if x>0:return x
  except:pass
  print("Enter a positive #")

def menu():
 while 1:
  try:
   x=int(input("Choose 1-5: "))
   if x>0 and x<6:return x
  except:pass
  print("Choose 1 to 5")

duckiedai_intro("CLAUSIUS CLAP")
print("CLAUSIUS-CLAPEYRON")
print("1 Find P2")
print("2 Find T2")
print("3 Find Hvap")
print("4 Find P1")
print("5 Find T1")
c=menu()

if c==1:
 p1=pos("P1: ")
 t1=pos("T1 K: ")
 t2=pos("T2 K: ")
 h=pos("Hvap kJ/mol: ")*1000
 try:
  p2=p1*exp((-h/R)*(1/t2-1/t1))
  print("P2 =",p2)
  print("P2/P1 =",p2/p1)
 except:print("P2 too large")

elif c==2:
 p1=pos("P1: ")
 p2=pos("P2: ")
 t1=pos("T1 K: ")
 h=pos("Hvap kJ/mol: ")*1000
 x=1/t1-(R/h)*log(p2/p1)
 if x<=0:print("T2 is not positive")
 else:
  t2=1/x
  print("T2 K =",t2)
  print("T2 C =",t2-273.15)

elif c==3:
 p1=pos("P1: ")
 p2=pos("P2: ")
 t1=pos("T1 K: ")
 t2=pos("T2 K: ")
 x=1/t2-1/t1
 if x==0:print("T1 and T2 differ")
 else:print("Hvap kJ/mol =",-R*log(p2/p1)/x/1000)

elif c==4:
 p2=pos("P2: ")
 t1=pos("T1 K: ")
 t2=pos("T2 K: ")
 h=pos("Hvap kJ/mol: ")*1000
 try:print("P1 =",p2/exp((-h/R)*(1/t2-1/t1)))
 except:print("P1 cannot display")

else:
 p1=pos("P1: ")
 p2=pos("P2: ")
 t2=pos("T2 K: ")
 h=pos("Hvap kJ/mol: ")*1000
 x=1/t2+(R/h)*log(p2/p1)
 if x<=0:print("T1 is not positive")
 else:
  t1=1/x
  print("T1 K =",t1)
  print("T1 C =",t1-273.15)

input("ENTER for guide: ")
print("QUICK GUIDE")
print("Use Kelvin only")
print("P units must match")
print("Higher T: higher P")
print("Hvap in kJ/mol")
print("DuckieDai: done!")
input("ENTER to exit: ")

from math import log,exp
R=8.314
def duckiedai_intro(program_name,wait=True):
title=program_name[:16]
empty=16-len(title)
left=empty//2
right=empty-left
print("+----------------------+")
print("| "+" "*left+title+" "*right+" |")
print("| |")
print("| __ |")
print("| ___(o )> quack! |")
print("| \\ <_. ) |")
print("| `---' |")
print("| by DuckieDai |")
print("+----------------------+")
print("Loading...")
if wait:
input("Press enter to start ")
print("\n"*6)
def pos(s):
while 1:
try:
x=float(input(s))
if x>0:return x
except:pass
print("Enter a positive #")
def menu():
while 1:
try:
x=int(input("Choose 1-5: "))
if x>0 and x<6:return x
except:pass
print("Choose 1 to 5")
duckiedai_intro("CLAUSIUS CLAP")
print("CLAUSIUS-CLAPEYRON")
print("1 Find P2")
print("2 Find T2")
print("3 Find Hvap")
print("4 Find P1")
print("5 Find T1")
c=menu()
if c==1:
p1=pos("P1: ")
t1=pos("T1 K: ")
t2=pos("T2 K: ")
h=pos("Hvap kJ/mol: ")*1000
try:
p2=p1*exp((-h/R)*(1/t2-1/t1))
print("P2 =",p2)
print("P2/P1 =",p2/p1)
except:print("P2 too large")
elif c==2:
p1=pos("P1: ")
p2=pos("P2: ")
t1=pos("T1 K: ")
h=pos("Hvap kJ/mol: ")*1000
x=1/t1-(R/h)*log(p2/p1)
if x<=0:print("T2 is not positive")
else:
t2=1/x
print("T2 K =",t2)
print("T2 C =",t2-273.15)
elif c==3:
p1=pos("P1: ")
p2=pos("P2: ")
t1=pos("T1 K: ")
t2=pos("T2 K: ")
x=1/t2-1/t1
if x==0:print("T1 and T2 differ")
else:print("Hvap kJ/mol =",-R*log(p2/p1)/x/1000)
elif c==4:
p2=pos("P2: ")
t1=pos("T1 K: ")
t2=pos("T2 K: ")
h=pos("Hvap kJ/mol: ")*1000
try:print("P1 =",p2/exp((-h/R)*(1/t2-1/t1)))
except:print("P1 cannot display")
else:
p1=pos("P1: ")
p2=pos("P2: ")
t2=pos("T2 K: ")
h=pos("Hvap kJ/mol: ")*1000
x=1/t2+(R/h)*log(p2/p1)
if x<=0:print("T1 is not positive")
else:
t1=1/x
print("T1 K =",t1)
print("T1 C =",t1-273.15)
input("ENTER for guide: ")
print("QUICK GUIDE")
print("Use Kelvin only")
print("P units must match")
print("Higher T: higher P")
print("Hvap in kJ/mol")
print("DuckieDai: done!")
input("ENTER to exit: ")

Filename: ccEQ.py
Size: 2167 bytes
SHA-256: 8cc5c176f0340878b9cc77812e2a04b48b406d072b87b10faab88b17d891f84f

Usage

Inputs

Two vapor pressures in the same unit
Absolute temperatures in kelvin
Enthalpy of vaporization in kJ/mol when supplied

Outputs

Requested pressure, temperature, or enthalpy of vaporization

Units: Pressure units may vary but must match; temperature is kelvin; enthalpy is kJ/mol; R is 8.314 J/(mol*K).

Assumptions and limitations

Assumptions

Delta Hvap is constant over the temperature interval.
The vapor behaves ideally and liquid molar volume is negligible relative to vapor.

Constraints

Pressures, temperatures, and supplied Delta Hvap must be positive; paired temperatures must differ when solving Delta Hvap.

Known failures

Wide temperature ranges, near-critical conditions, or phase changes can violate the approximation.
Extreme pressure ratios may overflow or underflow floating-point display.

Compatibility and review

Review status: Not calculator tested
Tested on: The owner reports personally testing the supplied archive programs on a calculator; exact model, OS, and Python App versions were not recorded
What happened: Owner reported interactive testing is disclosed, but the published bytes are not labeled independently calculator tested because the environment is unrecorded and Arrhenius received a narrow intake correction
Dependencies: math
Suggested calculator name: CCEQ — you can give it another valid, unique name when you transfer it
Desktop test cases: Not available for this interactive-only source

This exact source auto-launches an interactive calculator session, so compatibility evidence comes from the recorded physical-device review rather than an importable desktop fixture.

Transfer and launch

Download the .py file, send it to your calculator with TI Connect CE as CCEQ or another name, then open the Python App and try the worked example on this page first. This release has no verified calculator OS or Python App version; treat transfer and execution as unverified until independently tested.

Full installation and troubleshooting guide. Check your teacher's or exam's rules before using any program.

Version history

1.0.0 — current version, published 2026-09-23. Download this reviewed version

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