Heat of Vaporization: Definition & Equation

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: Inertial Frame of Reference: Definition & Example

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
Your next lesson will play in 10 seconds
  • 0:05 What Is Heat of Vaporization?
  • 0:47 Example
  • 3:13 By Substance
  • 3:43 Equation
  • 5:02 Lesson Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Speed Speed

Recommended Lessons and Courses for You

Lesson Transcript
Instructor: Jodie Stackhouse
In this lesson, you'll learn about the heat required to transform a liquid to its gas phase. Specifically, we'll explore the factors affecting heat of vaporization, including how to estimate it and how it changes between different substances.

What Is Heat of Vaporization?

Substances exist in three different phases: solid, liquid and gas. Heating and cooling a substance can transform it from one phase to another. Vaporization is the phase change that occurs when a liquid is transformed to a gas.

Substances require a specific amount of heat to undergo the physical changes necessary to switch phases. The energy or heat consumed per unit mass during the vaporization of a liquid is called heat of vaporization or enthalpy of vaporization. To condense water vapor to its liquid phase, energy must be removed from the gas. The energy per unit mass required to condense water vapor is equal to the heat of vaporization.

Heat of Vaporization Example

Water in a teapot undergoes an increase in temperature when heat is provided by the flame of your stove. Let's say we heat one kilogram of room temperature water to boiling in a teapot. In this graph, the temperature of one kilogram of water is plotted against the amount of heat absorbed.

Heat of Vaporization Graph

The graph shows three distinct parts:

  • Part I: First the temperature increases from room temperature to 100 degrees Celsius when boiling begins.

  • Part II: At this point, energy continues to be absorbed, but the temperature remains at 100 degrees. This is the case when the physical characteristics of water change in order to be transformed to vapor. The consumed heat is utilized to drive those changes.

  • Part III: After all the water is transformed to vapor (steam), the energy absorbed by the vapor is used to increase the temperature again.

Molecules must be rearranged and intermolecular forces such as ionic bonds, hydrogen bonds, and London dispersion forces must be broken for a substance to change phases. These changes are represented by the demand of energy. As you can see, the arrangement of molecules in solids is very different to that of liquids and gases. Molecules in a solid typically arrange in a periodic lattice, whereas in liquids, molecules do not have a periodic arrangement. Molecules in a gaseous substance move constantly, making their position hard to track.

Additionally, the strength of intermolecular forces between molecules is significantly higher in solids and liquids when compared to gases. Molecules in a liquid and a solid are close-packed due to strong intermolecular forces. In a gas, however, there are no intermolecular forces between molecules, and the average distance between molecules increases considerably.

The heat absorbed from a burning flame is used to break the intermolecular forces in water and increase the interatomic distance between water molecules. Because energy is being used to break intermolecular forces, there is no increase in temperature when water is boiling.

To unlock this lesson you must be a Study.com Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back
What teachers are saying about Study.com
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account