Modeling Energy Flow During Endothermic/Exothermic Reactions/Processes

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SWBAT define energy flow and depict energy flow using diagrams for endothermic and exothermic processes and reactions.

Big Idea

Direction of energy flow between the system and the surroundings defines whether a process or reaction is endothermic or exothermic.

Why This Lesson?

This lesson asks students to draw models of energy transfer, describing differences in energy flow between endothermic and exothermic reactions, directly using SEP 2 - Developing and Using Models and SEP 6 - Constructing Explanations.

In order to later address Performance Expectation HS-PS3-1, students will need a firm grasp on energy transfer.  This lesson results in students producing visual aids that will help reinforce the idea that energy can be transferred in the form of heat, and that exothermic processes result in an energy transfer from system to surroundings and vice versa for endothermic.


5 minutes

While I take attendance, students do a warm-up activity in their composition Warm-Up/Reflection books.  I use warm-ups to either probe for students' prior knowledge about the day's upcoming lesson or to have them bring to mind and review what they should have learned previously, either in class or during a flipped assignment.  (To read more about Warm Up and Reflection Books or Flipped Classroom, please see the attached resources.)

Yesterday’s homework assignment required the watching of a Zaption annotated video from the Crash Course Chemistry series:

This is a particularly great video because it explains endothermic and exothermic as it applies to real reactions and processes, with clear examples.  The information is also presented in a fun and engaging way with plenty of animated visuals and witty remarks from the host, Hank Green.  The Zaption application allows users to take any video that users upload or any video from YouTube and annotate it.  This is a Zaption that I made using the Crash Course Chemistry video already accessible from YouTube, including my own questions inserted.

<<reflection on using Zaption and how-tos>>

Today’s Warm-Up: “What is one example of an endothermic reaction or process?  What is one example of an exothermic reaction or process?"

In this case, the warm-up is asking students to recall that the video described several reactions and processes that are endothermic or exothermic.  I want students to be able to identify one of each, not necessarily directly from the video as long as they are correct.

If time permits, I walk around with a self-inking stamp to stamp the completed warm-ups indicating participation, but not necessarily accuracy.  In order to speed things up, my students have been trained to pass their books into the center of the table rows and stack them so that I can quickly pass by and stamp.  On days when there is too much business keeping, I do not stamp.  Students have been told that warm-ups are occasionally immediately checked and other times not.  At the end of each unit, Warm-Up/Reflection Books are collected and spot-checked.  



Introduction to the Activity

10 minutes

As part of the Zaption features, creators have access to a feature called "Analytics" which allows viewing of student answers to the questions included in the Zaption interactive video.  I have printed the list of student responses to the LAST question in the Zaption video: "Explain how energy flows differs between endothermic reactions and exothermic reactions."

I took this print out and cut the answers into strips, removing student names and only keeping student responses.  Now that I have strips of varying student answers, I pass them out to my students, one per student.  Each student has a different strip (that hopefully is not his or her own!) with an explanation of the differences between energy flow in endothermic and exothermic reactions written by another student.


I keep an extra strip, write it on the whiteboard, and then walk students through identifying potential inaccuracies in the statement and ways we could edit the statement.


Then, I handout Chemistry - Introduction to Endothermic & Exothermic Reactions.  I tell students to copy their strip as the answer to the first question on their handouts, then to rewrite the statement with any changes or additions to make the statement correct or stronger.  Students work to complete the first two questions of the handout.


Student Partner Work

30 minutes

I ask students to pair up and direct them to share their paper strips and their edits.  After, I tell students that they should work together to develop a final statement, which will be their answers to the third prompt on the handout.  I also tell students to work together to develop a diagram that will show energy flow in endothermic versus exothermic reactions, which they will draw in the boxes on the bottom of their handouts.

While students are working together on completing the handout and developing their models of energy flow, I circulate the room to answer questions, offer support, and ask probing questions to gauge student understanding.

Student work samples:

The top three are honors level chemistry samples.  The bottom two are general level chemistry samples.  All students were able to articulate direction of energy flow correctly, but the last sample shows diagrams that are not correct.  Here, the student shows freezing as endothermic and melting as exothermic.  I will need to help this student understand that even though students think of melting as "getting hotter," it is not releasing heat--it is absorbing heat which allows the motion of the molecules to increase causing phase change.

Student Reflection

5 minutes

In student's Warm-Up/Reflection Books, students should spend about 3-5 minutes writing a response to the day's reflection prompt.  Prompts are designed to either help students focus on key learning goals from the day's lesson or to prompt deeper thinking.  The responses also allow me to see if there are any students who are missing the mark in terms of understanding.  The collection of responses in the composition books can also show a progression (or lack thereof) for individual students. 

Today's Reflection Prompt:  "What is the direction of energy flow in endothermic reactions/processes compared to the direction of energy flow in exothermic reactions/processes?”

Desired student responses should include:

  • Energy flows from the system to the surroundings in exothermic reactions
  • Energy flows from the surroundings to the system in endothermic reactions


Almost all of my students could articulate the correct direction for heat flow in endothermic versus exothermic reactions.  The challenge will be helping them to remember that as we continue studying thermodynamics and beyond.