ALEX Lesson Plan

     

What Makes a Chemical Reaction Endothermic or Exothermic?

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  This lesson provided by:  
Author:Emily Menard
System: Homewood City
School: Homewood High School
The event this resource created for:ASTA
  General Lesson Information  
Lesson Plan ID: 34663

Title:

What Makes a Chemical Reaction Endothermic or Exothermic?

Overview/Annotation:

Students will analyze the bond energy of the reactants and products in a chemical reaction.  Students will develop a model to illustrate how the changes in total bond energy determine whether the reaction is endothermic or exothermic.

This lesson results from a collaboration between the Alabama State Department of Education and ASTA.

 Associated Standards and Objectives 
Content Standard(s):
Science
SC2015 (2015)
Grade: 9-12
Chemistry
11 ) Construct an explanation that describes how the release or absorption of energy from a system depends upon changes in the components of the system.

a. Develop a model to illustrate how the changes in total bond energy determine whether a chemical reaction is endothermic or exothermic.

b. Plan and conduct an investigation that demonstrates the transfer of thermal energy in a closed system (e.g., using heat capacities of two components of differing temperatures).

Insight Unpacked Content
Scientific And Engineering Practices:
Developing and Using Models; Planning and Carrying out Investigations; Constructing Explanations and Designing Solutions
Crosscutting Concepts: Cause and Effect; Systems and System Models; Stability and Change
Disciplinary Core Idea: Energy
Evidence Of Student Attainment:
Students:
  • Explain how the release or absorption of energy from a system depends on changes that occur in the components of the system.
  • Develop a model to illustrate how changes in total bond energy determine if a chemical reaction is endothermic or exothermic.
  • Plan an investigation and in the design decide on types, how much, and accuracy of data needed to produce reliable measurements.
  • Evaluate the investigation design to consider limitations on the precision of the data (e.g., number of trials, cost, risk, time) and to identify potential causes of apparent loss of energy from a closed system.
  • Conduct investigation as designed and if necessary, refine the plan to produce more accurate, precise, and useful data.
  • Use evidence from investigation to support the idea that the transfer of thermal energy when two components of different temperature are combined within a closed system results in a more uniform energy distribution among the components in the system.
Teacher Vocabulary:
  • System
  • Surroundings
  • Reactants
  • Products
  • Endothermic
  • Exothermic
  • Bond energy
  • Molecular collisions
  • Conservation of energy
  • Closed system
  • System boundaries
  • Components
  • Surroundings
  • Conservation of energy
  • Energy transfer
  • Thermal energy
Knowledge:
Students know:
  • Energy is a quantitative property of a system that depends on the motion and interactions of matter and radiation within that system. That there is a single quantity called energy is due to the fact that a system's total energy is conserved, even as within the system, energy is continually transferred from one object to another and between its various possible forms.
  • Models are developed based on evidence to illustrate the relationships between systems or between components of a system.
  • A stable molecule has less energy than the same set of atoms separated; one must provide at least this energy in order to take the molecule apart.
  • In chemical processes, whether or not energy is stored or released can be understood in terms of collisions of molecules and rearrangement of atoms into new molecules.
  • The energy change within a system is accounted for by the change in the bond energies of the reactants and products.
  • Breaking bonds requires an input of energy from the system or surroundings, and forming bonds releases energy to the system and surroundings.
  • The energy transfer between systems and surroundings is the difference in energy between bond energies of the reactants and products.
  • Although energy cannot be destroyed, it can be converted to less useful forms (i.e., to thermal energy in the surrounding environment).
  • The overall energy of the system and surroundings is conserved during the reaction.
  • Energy transfer occurs during molecular collisions.
Skills:
Students are able to:
  • Construct and revise an explanation based on valid and reliable evidence obtained from a variety of sources (students' own investigations, models, theories, simulations, peer review) and the assumption that theories and laws that describe the natrual world operate today as they did in the past and will continue to do so in the future.
  • Apply scientific principles and evidence to provide an explanation of phenomena.
  • Develop a model based on evidence to illustrate the relationships between systems or components of a system.
  • Describe relationships between system components to illustrate that the net energy change within the system is due to bonds being broken and formed, that the energy transfer between the system and surroundings results from molecular collisions, and that the total energy change of the chemical reaction system is matched by an equal but opposite change of energy in the surroundings.
  • Plan an investigation that describes experimental procedure (including safety considerations), how data will be collected, number of trials, experimental setup, equipment required, and how the closed system will be constructed and initial conditions of system.
  • Conduct an investigation to collect and record data that can be used to calculate the change in thermal energy of each of the two components of the system.
Understanding:
Students understand that:
  • Energy is a quantitative property of a system that depends on the motion and interactions of matter and radiation within that system. That there is a single quantity called energy is due to the fact that a system's total energy is conserved, even as within the system, energy is continually transferred from one object to another and between its various possible forms.
  • When investigating or describing a system, the boundaries and initial conditions of the system need to be defined and their inputs and outputs analyzed and described using models.
  • Models are developed based on evidence to illustrate the relationships between systems or between components of a system.
  • A stable molecule has less energy than the same set of atoms separated; one must provide at least this energy in order to take the molecule apart.
  • In chemical processes, whether or not energy is stored or released can be understood in terms of collisions of molecules and rearrangement of atoms into new molecules.
  • Uncontrolled systems always evolve toward more stable states (i.e., toward more uniform energy distribution).
  • The distribution of thermal energy is more uniform after the interaction of the hot and cold components.
  • Energy cannot be created or destroyed, but it can be trasported from one place to another and transferred between systems.
  • Scientists plan and conduct an investigation individually and collaboratively to produce data to serve as the basis for evidence and in the design, decide on types, how much, and accuracy of data needed to produce reliable measurements and consider limitations on the precision of data. Uncontrolled systems always evolve toward more stable states (i.e., toward more uniform energy distribution).
  • The distribution of thermal energy is more uniform after the interaction of the hot and cold components.
  • Energy cannot be created or destroyed, but it can be trasported from one place to another and transferred between systems.
  • When investigating or describing a system, the boundaries and initial conditions of the system need to be defined and their inputs and outputs analyzed and described using models.
AMSTI Resources:
ASIM Module:
This standard does not include calculating the total bond energy changes during a chemical reaction from the bond energies of reactants and products. 11b. Emphasis is on analyzing data from student investigations and using mathematical thinking to describe energy changes both quantitatively and conceptually. Examples could include mixing liquids at different initial temperatures or adding objects at different temperatures to water. Heat capacity values of components in the system should be obtained from scientific literature. Endothermic and Exothermic Reactions; Energy Content of Food; Hess's Law; Particle Collisions and Activation Energy; Excited electrons; Energy Changes in Simple Distillation; Elephant Toothpaste; Specific Heat

NAEP Framework
NAEP Statement::
P12.14: Chemical reactions either release energy to the environment (exothermic) or absorb energy from the environment (endothermic).

NAEP Statement::
P12.16: Total energy is conserved in a closed system.

NAEP Statement::
P12.5: Changes of state require a transfer of energy. Water has a very high specific heat, meaning it can absorb a large amount of energy while producing only small changes in temperature.


Local/National Standards:

Next Generation Science Standards

HS-PS1-4. Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy.

[Clarification Statement: Emphasis is on the idea that a chemical reaction is a system that affects the energy change. Examples of models could include molecular-level drawings and diagrams of reactions, graphs showing the relative energies of reactants and products, and representations showing energy is conserved.] [Assessment Boundary: Assessment does not include calculating the total bond energy changes during a chemical reaction from the bond energies of reactants and products.]

Primary Learning Objective(s):

Learning Targets:

  • I can develop a model to illustrate how changes in total bond energy determine whether a reaction is endothermic or exothermic.
  • I can identify that in a chemical reaction bonds are broken in the reactants requiring an input of energy and bonds are formed in the products releasing energy.

Additional Learning Objective(s):

 
 Preparation Information 

Total Duration:

61 to 90 Minutes

Materials and Resources:

Index cards

Adhesive magnetic strips (or small magnets)

Adhesive velcro strips

250 mL beakers (2 per group)

Vinegar (20 mL per group)

Baking Soda (2.0 grams per group)

Calcium chloride (0.5 grams per group)

Water

Temperature probes or thermometers (1 per group)

Technology Resources Needed:

Background/Preparation:

  • 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).  
  Procedures/Activities: 

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.   



Attachments:
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  Assessment  

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.