Unit Overview
7.2 Chemical Reactions & Energy

How can we help people make a flameless heater?

Unit Summary

*This unit is being revised based on the data from our field test.
This unit on chemical reactions and energy starts off with students thinking about how they would heat up food without having typical methods available. Then they see images from a real
situation, after Superstorm Sandy in New York, during which people were given Meals, Ready-to-Eat (MREs) that can heat up food by just adding water. The class explores the flameless heater from the MRE in action, which seems like some kind of chemical process or possibly a chemical reaction. Students develop an initial model to consider how a flameless heater works, but they also notice some problems with prepackaged MREs. In order to solve some of the identified problems, the class decides to help people in situations in which typical heating methods aren’t available to heat up food by designing a homemade flameless heater with instructions that others could follow.
Throughout this unit, students:
•analyze data to determine patterns in the relationship between the total amount of food they can heat and the amount of energy that is transferred from the chemical reaction to the
food system;
•undertake a design project to construct and test a solution that meets specific design criteria and constraints, including the transfer of energy;
•respectfully provide and receive critiques about design solutions with respect to how they meet criteria and constraints and consider patterns across multiple designs to determine
which design characteristics cause more effective outcomes in performance; and
•optimize the performance of a design that transfers energy through a system by prioritizing criteria, making trade-offs, testing, revising, and re-testing

Additional Unit Information

Building Toward the Following Standards and Practices
Performance Expectations

This unit builds towards the following NGSS Performance Expectations (PEs):

  • MS-PS1-6: Undertake a design project to construct, test, and modify a device that either releases or absorbs thermal energy by chemical processes.
  • MS-ETS1-2: Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem.
  • MS-ETS1-3: Analyze data from tests to determine similarities and differences among several design solutions to identify the best characteristics of each that can be combined into a new solution to better meet the criteria for success.
  • MS-ETS1-4: Develop a model to generate data for iterative testing and modification of a proposed object, tool, or process so that an optimal design can be achieved.
Disciplinary Core Ideas

This unit expands students’ understanding of energy in chemical reactions in the context of engineering design. These are the Grades 6-8 DCI elements:

PS1.B: Chemical Reactions

  • Some chemical reactions release energy, while others store energy.

ETS1.B: Developing Possible Solutions

  • Models of all kinds are important for testing solutions.
  • A solution needs to be tested and then modified on the basis of the test results in order to improve it.
  • There are systematic processes for evaluating solutions with respect to how well they meet the criteria and constraints of a problem.
  • Sometimes parts of different solutions can be combined to create a solution that is better than any of its predecessors.

ETS1.C: Optimizing the Design Solution

  • Although one design may not perform the best across all tests, identifying the characteristics of the design that performed the best in each test can provide useful information for the redesign process—that is, some of the characteristics may be incorporated into the new design.
  • The iterative process of testing the most promising solutions and modifying what is proposed on the basis of the test results leads to greater refinement and ultimately to an optimal solution.

You can view the placement of this OpenSciEd Unit 7.2 and associated units within the OpenSciEd Scope and Sequence document

Focal Science and Engineering Practices
  • Planning and Carrying Out Investigations
  • Constructing Explanations and Designing Solutions
Focal Crosscutting Concepts
  • System and System Models
  • Matter and Energy
Unit Information
What should my students know from earlier grades or units?

This unit directly builds on ideas that students figured out in 6.2 Thermal Energy and 7.1 Chemical Reactions & Matter. If your students have not done those units prior to beginning this unit, it is critical to supplement their understanding of the following DCIs: 

PS1.A Structure and Properties of Matter

  • Substances are made from different types of atoms, which combine with one another in various ways. 
    • This unit uses chemical formulas to describe various substances and reactions that students investigate. Students should understand that substances are made up of atoms and be familiar with seeing atomic symbols to represent substances. 
  • Gases and liquids are made of molecules or inert atoms that are moving about relative to each other. 
    • This unit includes sensemaking around gases, liquids, and solids. It is critical that students know that all states of matter are made of particles, even if we cannot see them. 

PS1.B Chemical Reactions

  • Substances react chemically in characteristic ways. In a chemical process, the atoms that make up the original substances are regrouped into different molecules, and these new substances have different properties from those of the reactants. 
    • Students use this prior knowledge to determine if a chemical reaction is taking place in the MRE heater. Then the class figures out how to design a homemade device that transfers energy using a chemical reaction
  • The total number of each type of atom is conserved, and thus the mass does not change. 
    • Students account for the conservation of matter in the reaction between the copper sulfate (root killer) and aluminum. They should have prior knowledge that no “new” matter is being created nor destroyed during a chemical process; rather, molecules are breaking apart and rearranging. 

PS3.A: Definitions of Energy

  • The term “heat” as used in everyday language refers both to thermal energy (the motion of atoms or molecules within a substance) and the transfer of that thermal energy from one object to another. In science, heat is used only for this second meaning; it refers to the energy transferred due to the temperature difference between two objects. 
    • In this unit, students track energy transfers into or out of the various systems involved (the substances themselves, as well as the cup holding them, the air, the thermometer, etc.) to help figure out that the energy from a chemical process could be transferred to heat up the food in our homemade Meal, Ready-to-Eat. 
  • Temperature is a measure of the average kinetic energy of particles of matter. The relationship between the temperature and the total energy of a system depends on the types, states, and amounts of matter present. 
    • Students should come into the unit understanding that an increase of the average kinetic energy of particles of matter would show a higher temperature. Models at the particle level are used to compare when more or less energy is transferred from the chemical process system to the surrounding systems (e.g., packaging materials, food, thermometer, etc.). 
  • The temperature of a system is proportional to the average internal kinetic energy and potential energy per atom or molecule (whichever is the appropriate building block for the system’s material). The details of that relationship depend on the type of atom or molecule and the interactions among the atoms in the material. Temperature is not a direct measure of a system’s total thermal energy. The total thermal energy (sometimes called the total internal energy) of a system depends jointly on the temperature, the total number of atoms in the system, and the state of the material.  
    • Students will model the movement of molecules at different temperatures, indicating an increase in speed at higher temperatures. 

PS3.B: Conservation of Energy and Energy Transfer

  • Energy is spontaneously transferred out of hotter regions or objects and into colder ones. The amount of energy transfer needed to change the temperature of a matter sample by a given amount depends on the nature of the matter, the size of the sample, and the environment. 
    • In Lesson 5 students will further investigate how the amount of energy transfer needed to change the temperature of matter depends on the size of the sample—they analyze data of energy transfer from a chemical reaction to various amounts of food. However, it is assumed that students understand how energy transfers from hotter regions or objects into colder ones through particle collisions. 
  • When the motion energy of an object changes, there is inevitably some other change in energy at the same time. 
    • This DCI element is applied at the particle level when students are thinking about how to maximize or minimize energy transfer in their homemade heaters. 

ETS1.A: Defining and Delimiting Engineering Problems

  • The more precisely a design task’s criteria and constraints can be defined, the more likely it is that the designed solution will be successful. Specification of constraints includes consideration of scientific principles and other relevant knowledge that are likely to limit possible solutions. 
    • It would be helpful to have prior exposure to this DCI element built into the 6.2 Thermal Energy or 6.5 Natural Hazards. If students have not encountered this DCI before, then extra support in defining criteria and constraints will be needed in Lesson 1. 

It will be helpful to have students familiar with using the following focal crosscutting concepts (CCCs) for this unit, specifically around the elements listed here from the 3-5 grade-band. Systems and System Modeling has been listed here because this is an important lens for students to work with in the unit as well. 

Energy and Matter  

  • Matter is made of particles.  
  • Matter flows and cycles can be tracked in terms of the weight of the substances before and after a process occurs. 
  • The total weight of the substances does not change. This is what is meant by conservation of matter. Matter is transported into, out of, and within systems.  
  • Energy can be transferred in various ways and between objects.
  • Matter is conserved because atoms are conserved in physical and chemical processes (from the 6-8 grade-band).

Systems and System Models

  • A system is a group of related parts that make up a whole and can carry out functions its individual parts cannot.  
  • A system can be described in terms of its components and their interactions.

Students should be familiar with using the following focal science and engineering practices (SEPs) for this unit, specifically around the elements listed here from the 3-5 grade-band.

Planning and Carrying Out Investigations

  • Plan and conduct an investigation collaboratively to produce data to serve as the basis for evidence, using fair tests in which variables are controlled and the number of trials considered.
  • Evaluate appropriate methods and/or tools for collecting data. 
  • Make observations and/or measurements to produce data to serve as the basis for evidence for an explanation of a phenomenon or test a design solution.
  • Make predictions about what would happen if a variable changes.
  • Test two different models of the same proposed object, tool, or process to determine which better meets criteria for success.

Constructing Explanations and Designing Solutions

  • Construct an explanation of observed relationships. 
  • Use evidence (e.g., measurements, observations, patterns) to construct or support an explanation or design a solution to a problem.
  • Identify the evidence that supports particular points in an explanation.
  • Apply scientific ideas to solve design problems.
  • Generate and compare multiple solutions to a problem based on how well they meet the criteria and constraints of the design solution.
What are some common ideas that students might have?

This unit will focus a great deal on energy transfer between systems. However, at the start of this unit, students may or may not identify the heater and food as two distinct systems, and they may not yet name energy transfer as the cause for the food heating up. Working with students to use the CCC lens of Systems and System Models will help them accurately identify energy transfers to and from chemical reactions. 

A common partial understanding students may have is that, during an exothermic reaction, when the thermometer detects a temperature increase, energy is being put into the system in order for it to feel warmer. This seems logical at first because in the 6.2 Thermal Energy unit students learned that, when objects heat up, energy is being transferred to them. The difference here is that the system of reactants itself is not gaining energy—the system releases energy so that the other surrounding systems, such as the environment, thermometer, and food items, get energy transferred to them and, thus, heat up. As the unit progresses, students will identify that, during an exothermic reaction, energy is transferred to other systems from the chemical reaction system. For instance, the chemical reaction system transfers energy to the thermometer, its container, the outside environment, and the food. That’s why those objects feel warmer. 

What modifications will I need to make if this unit is taught out of sequence?

This is the second unit taught in 7th grade in the OpenSciEd Scope and Sequence. If this unit is taught earlier in the middle-school curriculum, the following modifications would need to be made: 

  • Introducing the students to the concept of a Driving Question Board and a shared set of classroom norms. This would not be necessary if taught after other OpenSciEd units.
  • Supplemental teaching of several PEs from 6.2 Thermal Energy: 
    • MS-PS1-4: Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.
    • MS-PS3-3: Apply scientific principles to design, construct, and test a device that either minimizes or maximizes thermal energy transfer. 
    • MS-PS3-4: Plan an investigation to determine the relationships among the energy transferred, the type of matter, the mass, and the change in the average kinetic energy of the particles as measured by the temperature of the sample.
    • MS-PS3-5: Construct, use, and present arguments to support the claim that, when the kinetic energy of an object changes, energy is transferred to or from the object.
    • MS-ETS1-1: Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment that may limit possible solutions. 
  • Supplemental teaching of several PEs from 7.1 Chemical Reactions & Matter:
    • MS-PS1-1: Develop models to describe the atomic composition of simple molecules and extended structures. Chemical formulas of substances are used in this unit. It is assumed that students understand the DCI element that substances are made from different types of atoms, which combine with one another in various ways.    
    • MS-PS1-2: Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred. This unit does not teach students how to identify if a chemical reaction has occurred. Students use this previous knowledge and apply it to new phenomena to determine if the chemical processes they observe are, in fact, chemical reactions. Students may start to recognize chemical reactions as early as Lesson 1 while observing the MRE heater, which gives off hydrogen gas as a product. This is an indication that the MRE heater is undergoing a chemical reaction, which students should recognize from their prior experiences in 7.1 Chemical Reactions & Matter.
  • Make sure students have the necessary common-core 6th-grade math concepts regarding ratios and proportions. For more details, see the following section about prerequisite math concepts necessary for the unit. 
What are the prerequisite math concepts necessary for the unit?

In Lesson 3, students calculate the maximum temperature change for three different amounts of reactants. They report this change in temperature using positive and negative numbers to show the increase or decrease from the starting temperature. Prerequisite math concepts that may be helpful include the following:

  • CCSS.MATH.CONTENT.6.NS.C.5 Understand that positive and negative numbers are used together to describe quantities having opposite directions or values (e.g., temperature above/below zero, elevation above/below sea level, credits/debits, positive/negative electric charge); use positive and negative numbers to represent quantities in real-world contexts, explaining the meaning of 0 in each situation.

 

In Lesson 4, students determine the relative proportion of each reactant that showed the optimal temperature change by calculating the percentage of each reactant. Prerequisite math concepts that are needed include the following:

  • CCSS.MATH.CONTENT.6.RP.A.3.C Find a percent of a quantity as a rate per 100 (e.g., 30% of a quantity means 30/100 times the quantity); solve problems involving finding the whole, given a part and the percent.

 

In Lesson 6 and Lesson 9, students will scale up the amount of reactants to use in their homemade heaters but maintain the same proportion of reactants they found to be most efficient in previous testing.  Furthermore students then scale down amounts to test their prototypes.  Prerequisite math concepts that may be helpful include the following:

  • CCSS.MATH.CONTENT.6.RP.A.3 Use ratio and rate reasoning to solve real-world and mathematical problems, e.g., by reasoning about tables of equivalent ratios, tape diagrams, double-number line diagrams, or equations.
  • CCSS.MATH.CONTENT.6.RP.A.3.A Make tables of equivalent ratios relating quantities with whole-number measurements, find missing values in the tables, and plot the pairs of values on the coordinate plane. Use tables to compare ratios.

In Lesson 6 and Lesson 9, students will need to calculate the correct amounts of water beads and plain water to make “water bead soup” as a proxy for food in their prototype heaters. The ratio of water beads to plain water is 1:3 (1 part water beads to 3 parts water), and students will measure the beads and water in grams. Prerequisite math concepts that may be helpful include the following:

  • CCSS.MATH.CONTENT.6.RP.A.1 Understand the concept of a ratio and use ratio language to describe a ratio relationship between two quantities. For example, “The ratio of wings to beaks in the bird house at the zoo was 2:1, because for every 2 wings there was 1 beak.” “For every vote that candidate A received, candidate C received nearly three votes.”
  • CCSS.MATH.CONTENT.6.RP.A.3.D Use ratio reasoning to convert measurement units; manipulate and transform units appropriately when multiplying or dividing quantities.

 

In Lesson 9, students may want to redesign their homemade heaters to increase the surface area of the reactant system that is in contact with the food system. While mathematical calculation of surface area will not be necessary for these design improvements, it may be helpful if students understand the concept of surface area. As such, the following standard may provide a connection point:

  • CCSS.MATH.CONTENT.7.G.B.6 Solve real-world and mathematical problems involving area, volume, and surface area of two- and three-dimensional objects composed of triangles, quadrilaterals, polygons, cubes, and right prisms.