Endothermic and Exothermic Reactions

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: What is Energy? - Definition and Significance in Nature

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

Take Quiz Watch Next Lesson
Your next lesson will play in 10 seconds
  • 0:08 Chemical Reactions
  • 0:47 Exothermic and…
  • 2:41 Enthalpy
  • 4:26 Lesson Summary
Add to Add to Add to

Want to watch this again later?

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

Login or Sign up


Recommended Lessons and Courses for You

Lesson Transcript
Instructor: Amy Meyers

Amy holds a Master of Science. She has taught science at the high school and college levels.

Explore a chemical reaction at the molecular level. Learn about exothermic and endothermic reactions, what they look like and what happens when they occur. Understand enthalpy and how you can use it to predict whether a reaction will be exothermic or endothermic.

Chemical Reactions

A chemical reaction is when one or more substances are changed into one or more different substances. To know for certain that a reaction has happened, you need to have evidence that a substance has changed identity. Although you could analyze the products to make sure it has changed identity, you can also look for other clues to tell you.

One of the laws of science is the law of conservation of energy, which states that in any chemical or physical process, energy is neither created nor destroyed. What this means is that if energy of the system decreases, then the energy of the surroundings increases by the same amount.

Exothermic and Endothermic Reactions

If two substances combine and heat and light are produced, this is strong evidence that a reaction has taken place. If heat is given off, the reaction is exothermic. Exothermic means that during the reaction, molecules have moved from a higher state of energy to a lower state. An endothermic reaction is the opposite. This is when a reaction starts colder and ends up hotter, taking in energy from start to finish.

In an endothermic reaction, the system gains heat as the surroundings cool down. In an exothermic reaction, the system loses heat as the surroundings heat up.

That ice pack the coach is putting on the batter? It's an example of an endothermic reaction. An endothermic reaction is when heat is needed by the reaction, so it draws heat from its surroundings, making them feel cold. Just like that ice pack.

An example of an endothermic reaction
Endothermic Reaction

Oh, look, it was the boy's birthday, and they're celebrating at the ball park. His mother is lighting the candles. See that lit candle? That is an example of an exothermic reaction. Exothermic reactions give off heat.

An example of an exothermic reaction
lighting birthday cake candles

At the molecular level, an exothermic reaction is when a bond is formed. When two things come together, they're happier and take less energy to stay together. Since we have the conservation of energy law, we know that the energy they don't need has to go somewhere, so they give it off to their surroundings.

As we all know, it is easier to get together than to break up. It takes energy to break up. Just like when a chemical bond is broken, it needs energy to break. This is an endothermic reaction.

Another way to look at exothermic and endothermic reactions is to think of two magnets. If the magnets are stuck together, then it takes energy to pull them apart, just like it takes energy to break bonds. If the magnets are apart, they like to be together and actually pull each other together, releasing energy in the process. This is like the making of chemical bonds.

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 160 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