What Makes a Chemical Reaction Endothermic or Exothermic?
You may save this lesson plan to your hard drive as an html file by selecting
"File", then "Save As" from your browser's pull down menu. The file name extension
must be .html.
Students should have a clear understanding of the difference between physical changes and chemical changes.
Students should know how to write and balance chemical equations.
Students should be comfortable with the law of conservation of energy.
Teacher Preparation for follow-up activity: Take index cards and cut into strips that are about the same width of the adhesive velcro and magnetic strips. Put a piece of velcro on one side of the index card strip and a piece of magnetic strip on the opposing side. Ensure that you have enough for each group to have a set of 2 that will stick together on both sides. (The velcro on one index card attaches to the velcro on the other index card and the magnet on the back of the card sticks to the magnet on the back of the other card).
Before:
Show students the ACS Video: Exothermic & Endothermic Reactions to introduce the idea of bond energy in relation to a reaction being classified as either endothermic or exothermic.
As students watch the video they should complete a Venn diagram on the two types of reactions. After the video, students should work with a partner using the strategy: think, pair, share to discuss what they saw in the video.
Following partner discussions engage the class in a whole class discussion where groups share what they learned from the video. This will allow the teacher to assess what students know and think prior to the lab activity.
During:
Students will complete a lab activity on endothermic and exothermic reactions with their lab partner. See the attached document "Bond-energy-endothermic-exothermic" for directions.
During the activity students will react sodium bicarbonate with acetic acid and then react sodium bicarbonate solution with calcium chloride to see an example of an endothermic and exothermic reaction. Ensure that students wear goggles and lab aprons in the laboratory and follow all appropriate safety precautions. Following the experiment, students will write the balanced chemical equation for each reaction, identify the type of reaction that has occurred and analyze the bond energy requirements. As a result of the lab activity, students will develop a model to illustrate how changes in total bond energy determines whether a reaction is endothermic or exothermic.
After: Give each group of students 2 of the index card strips that have velcro on one side and a magnetic strip on the other. Have students determine which side (magnet or velcro) takes more energy to pull apart when they are connected and have them relate this to the breaking of bonds in the reactants. Then have students analyze which side (magnet or velcro) is easier to put together and have them relate this to the formation of bonds in the product. You can include technology in this step of the lesson by using a poll on Kahoot, Socrative, or Google forms to collect data from the class. Discuss with students why the reason for their selection to be easier to put together and their comparison to the bond types. This discussion will help you formatively assess student understanding of the bond types. Review endothermic and exothermic reactions with students based on the overall energy change from the reactants to the products.
Assessment Strategies
Students will be formatively assessed during think, pair, share activity during the introduction phase of the lesson.
Student will be assessed formally on the lab activity and model developed for endothermic and exothermic reactions based on the worksheet that they turn in.
Student will be informally assessed based on descriptions given during the velcro/magnet activity as the teacher discusses why the velcro or magnet is an "easier" bond to form and the student makes comparisons between that model and the bond types.
Acceleration:
Students who are already familiar with bond types and reaction types or who learn quickly can extend their study on energy by watching the ACS video: Meet a BP Chemist to give students an idea of what a chemist who works with energy does on a daily basis.
Intervention:
Students who need extra assistance based on formal and informal assessments with the teacher should have individual or small group focused instruction with the teacher to clarify bond types and reaction types.
View the Special Education resources for
instructional guidance in providing modifications and adaptations
for students with significant cognitive disabilities who qualify for the Alabama Alternate Assessment.