# Isotherm, Isobar & Isochore graphs

When we study gas laws (Boyle’s law, Charles’ law & Pressure Law), we come across terms like Isotherm, Isobar, and Isochore. Here, in this post, we will discuss these.

## What is Isotherm?

If we draw Boyle’s law graphs at diff temperatures then we get curves shown in figure 1.

Boyle’s law is expressed as **V = k_{1} / p** where V is the volume,

*p*is the pressure of the gas and

*k*

_{1}is a constant of proportionality whose value depends upon the amount of the gas and temperature.

The value of k_{1} for each curve is different (because for a given mass of gas it varies only with temp).

* Each p-V curve of Boyle’s law graphs corresponds to a different constant temperature and is known as an isotherm.* Higher curves correspond to higher temp.

## What is Isobar?

If we draw Charles’ law graphs at different pressures then we get curves shown in figure 2.

Charles’ law is expressed as **V = k_{2} T** where V is the volume,

*T*is the temperature of the gas and

*k*2 is a constant of proportionality.

These Charles’ law curves are Volume vs temperature (°C) graphs for different pressures.

*Each line of the Charles’ law graphs *or *Volume vs Temperature graphs corresponds to a different constant pressure and is called isobar.*

## What is Isochore?

If we draw Pressure law graphs at different volumes then we get curves shown in figure 3.

Pressure law is expressed as **P = k_{3} T** where P is the pressure,

*T*is the temperature of the gas and

*k*

_{3}is a constant of proportionality.

These Pressure law curves are Pressure vs temperature (°C) graphs for different volumes.

*Each line of the Pressure law graphs *or *Pressure vs Temperature graphs corresponds to a different constant volume and is called isochore.*