Ideal Gas Under Constant Pressure Example Problem

Worked Chemistry Problems

Close-Up Of Balloons Against Sky
Balloons are often used as Ideal Gas Law examples. Getty Images/Kittiyut Phornphibul/EyeEm

Here is an example of an ideal gas problem where the pressure of the gas is held constant.

Question

A balloon filled with an ideal gas at a temperature of 27 °C at 1 atm of pressure. If the balloon is heated to 127 °C at constant pressure, by what factor does the volume change?

Solution

Step 1

Charles' Law states

Vi / Ti = Vf / Tf where

Vi = initial volume
Ti = initial temperature
Vf = final volume
Tf = final temperature

Step 1

Convert temperatures to Kelvin

K = °C + 273

Ti = 27 °C + 273
Ti = 300 K

Tf = 127 °C + 273
Tf = 400 K

Step 2

Solve Charles' Law for Vf

Vf = ( Vi / Ti ) / Tf

Rearrange to show final volume as a multiple of initial volume

Vf = ( Tf / Ti ) x Vi

Vf = ( 400 K / 300 K) x Vi
Vf = 4/3 Vi

Answer:

The volume changes by a factor of 4/3.