7th Grade Science : Unit #6 - Chemical Properties and Reactions : Lesson #2

Chemical vs Physical Changes Group Challenge

Objective: Students will be able to cite evidence in order to determine if a reaction as a chemical or physical change and identify that the properties of the reactants and products of a reaction are different.
Standards: RST.6-8.1 WHST.6-8.1.b WHST.6-8.9 MS-PS1-2 SP1 SP8 XC-P-MS-1
Subject(s): Science
60 minutes
1 Introduction and Connection to the NGSS and Common Core - 0 minutes

In this lesson, students utilize text reading strategies to build their understanding of chemical and physical changes.  In addition, students participate in a fun reaction identification game that gives students with lots of practice at identifying chemical and physical reactions!

This lesson is designed to connect to the following NGSS and Common Core Standards:

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.

CCSS.ELA-LITERACY.RST.6-8.1  Cite specific textual evidence to support analysis of science and technical texts.

CCSS.ELA-LITERACY.WHST.6-8.1.B  Support claim(s) with logical reasoning and relevant, accurate data and evidence that demonstrate an understanding of the topic or text, using credible sources.

CCSS.ELA-LITERACY.WHST.6-8.9  Draw evidence from informational texts to support analysis, reflection, and research.

Science and Engineering Practices:

When using the text strategies utilized in this lesson, students think deeply about text in order to make their own conclusions and consider solutions to problems.  Thus, students are using the scientific principle of Generating Questions and Designing Solutions which states that "Students at any grade level should be able to ask questions of each other about the texts they read, the features of the phenomena they observe, and the conclusions they draw from their models or scientific investigations." (SP1)   In addition, when utilizing text, students use strategies to obtain scientific information and evidence from text (SP8).  

Crosscutting Concepts:

In identifying evidence of chemical reactions and the properties that may change in various reactions, students can begin to see patterns in what types of evidence are signs of a chemical change. (Patterns)  Moreover, when students utilize text strategies, they generate thoughtful questions that take them "beyond the text" by making connections to the NGSS Cross Cutting Concepts as they read.  Examples of connections made by students in this lesson include "Patterns", "Cause and Effect", and "Scale, Proportion, and Quantity".

2 Connecting to the Essential Question: What are you supposed to learn today? - 5 minutes

Ask students, "What are you going to learn today?".  Students should respond by saying that they will be answering the Essential Question, "How do particles combine into new substances? And, what evidence can show how the physical and chemical properties of the substances change?"  This EQ is posted on my board and on the student's Chemistry Unit Plan

Explain to students that this lesson represents the second lesson that students work with Skill 5 of the Chemistry Unit Plan, "I can provide evidence to show if a reaction is a chemical or physical change."  Have the students turn to their unit plans and silently read the skill.  After reading the skill have the students rank their current level of mastery on a scale of 1 to 4 (4 being mastery).  Students in my room have already assessed themselves in the lesson prior to this; this would be an opportunity for the student to change their number if they felt their level of mastery had increased after the previous lesson.

In my classroom, students frequently self-assess their level of understanding on each skill in the unit as we go.  As you can see from the image below, this student ranks themself as a "2" to start this lesson.  As we work more on this skill in the upcoming lessons, the student will re-assess and update this score.


For a look at all the lessons that have led my students to this point and where we go from here check out the lessons in these units:

Physical Properties:  Molecular Arrangement and Phase Changes:  Focuses on Skills 1 - 4 of the Chemistry Unit Plan

This unit is designed to answer the Essential Question, "How do particles combine into new substances? What evidence can show how the physical and chemical properties of the substances change?". It particularly focuses on types of matter, physical properties, phase changes, and factors that affect physical properties. This unit's purpose is so much more than just the content, however. It's focus is scientific literacy. It stresses group discussion, discourse and utilizing text references when engaging in argument. Students utilize reading, writing, and speaking strategies in order to develop scientific literacy. It's scientific literacy immersion!

Chemical Properties and Reactions:  Focuses on Skills 4 - 6 of the Chemistry Unit Plan.

This unit is also designed to answer the Essential Question, "How do particles combine into new substances?  What evidence can show how the physical and chemical properties of the substances change?".  This unit focuses on chemical properties and chemical reactions.  Students analyze evidence and property changes that allow them to distinguish between chemical and physical reactions.  In addition, students investigate the Law of Conservation of Mass as they look at how bonds are broken and formed in chemical reactions.  This unit is full of hands on labs and station rotations that will engage any middle school student in chemistry.

Unit Plans , Essential Questions and "I Can" Statements
Unit Planning

In developing a unit plan, there are some critical elements that can help your unit be successful. The first is an "Essential Question".  Having a big idea that is the focus of learning gives students purpose in each lesson.  Post this question in your room and refer to it daily!  This can help students see that each lesson is part of a bigger plan and that they are searching for depth about a big idea.  To help with this, the NGSS has already created these in the "Storyline" of each topic that includes an "Essential Question" for each topic! Next, "I can" statements help students have a clear idea of what they need to do in order to develop the answer to the essential question.  I have found that "I can" statements are the most successful format for objectives for middle school students.  It is important for I can statements to be written clearly (at middle school understanding level) and explicitly, using vocabulary that tells the student what they have to be able to do.

It is more than just creating an EQ and "I can" statements though.  The success in your unit will revolve around your use of these tools.  If only referenced at the beginning of a unit or printed on a paper that is "shoved" in the students' binders, your students will never reach the level of mastery that you are seeking.  You see, students can hit a target that they know is there.  They can make plans for reaching it and reflect on their progress.  They will make connections to standards across multiple lessons over the course of the unit as opposed to feeling as if each lesson is in isolation. Thus, your unit can become one of growth rather than "hit or miss".  Moving or invisible targets - well, those are easy to miss.  Make your targets clear and understandable.

Use your Essential Questions and "I Can" statements on a daily basis!  Your students learning will be positively affected!

3 Mini Lesson: Talk to the Text, Ladder of Discourse and Chemical Reactions - 25 minutes

Ask students to turn to their Skill CH.5 Notes Page.  In my class, at this point in the year, we have been working hard on obtaining information and meaning from text.  I tell my students that today's lesson is an opportunity for them to demonstrate independence with this skill.

When reading students must *"talk to the text" and climb the *"Ladder of Discourse".  The levels of the ladder are "Tweets" (text to self connections), "Huh?'s" (questions or concepts they do not understand), "Found It" (finding answers to questions through context clues or finding science answers), and "Discourse" (combining ideas to think beyond the text).  A deeper description of these levels can be found in the Ladder of Discourse document in the resource section.

Talking to the Text and Ladder of Discourse Student Examples:


This student asks the question, "How do you know the bonds change if you can't see them?".  

Found it!:

This student's "Found it!" connects the reading to a previous "flash freeze" experiment we had completed in class.


In my class we have really been working on "Discourse".  The "Discourse" rung of the ladder is definitely the most challenging of the rungs as it asks students to think beyond the text.  Part of "Discourse" can be generating questions based on the Cross Cutting Concepts of the NGSS.  Scientists are constantly making connections to these Cross Cutting Concepts in their reading and in their analysis of data.  Thus, students are asked to connect to these ideas here.  Below are some comments students made as a result of thinking about the NGSS Cross Cutting Concepts.

Quantity, Scale and Proportion:

This student wonders if you doubled the reactants, if the products would be doubled as well.  In other words, would there be a proportional relationship.

This student wonders if changing the quantity of dry ice in a balloon would affect the rate at which it inflates.


This student notices a pattern in the text.  She notes that the text always mentions bonds when talking about chemical changes.

This student notes a pattern that all of the things that can cause physical changes have something in common.  As the student says, "non of these change the object itself".  This is an incredible pattern to notice that goes to the heart of the difference between a chemical and physical change.

This student notices a pattern in the text that when describing physical reactions, the author keeps saying, "the substance is still the same".


Cause and Effect:

This student notices that adding and removing energy is a cause that creates and effect on physical properties.

 *For more background on "talking to the text" and the "Ladder of Discourse" check out the following lessons.  These lessons include videos of me demonstrating these strategies and student work.

Talking to the Text:  Mystery Box Modeling:  Energy TransformationsHow does heat move?Thermal Protection Systems

Ladder of Discourse:  Polymer PropertiesSugar, Solutes, Satisfaction!Refracting TelescopesEngineering Earthquake Structures

4 Chemical or Physical Reaction? Group Activity - 45 minutes

This group activity provides students with lots of practice classifying reactions as chemical or physical while making it into a game!


  1. Break students into groups of 2 - 4.  Try not to have any groups larger than four as the more students are in the group the less accountability each child has in the activity.
  2. Each group is given a packet of four sheets that have a list of reactions on them. 
  3. Students begin with page #1 and identify whether each is chemical or physical reactions.  Groups must discuss their ideas to come to a consensus.
  4. When a group is finished with the first page, they raise their hand and WAIT for the teacher.  Students should not move on to the next page until given approval.
  5. The teacher checks the group’s work, but DOES NOT tell the group which items they got wrong, ONLY how many they got wrong.  The teacher should write this number on the page.
  6. The group is then given time to go back through the list to decide which items they feel are incorrect.  The group makes changes and then raises their hands again.
  7. The teacher then returns to the group to review their work.  At this visit, the teacher informs the students if they correctly changed their answers.  If the group still has any items wrong, the teacher should explain the error to the group.
  8. Scoring:  If students correct their errors, they can earn half of a point back.  However, if they change an answer that was correct, they lose an entire point.  Here are some examples of scoring.
    • A group misses 4 items on the first page.  Then, they correctly change the items that were wrong.  The students would then lose only 2 points on the first page.
    • A group misses 2 items on the first page.  Then, they correctly change one of the incorrect items, but also change an item that was previously correct to an answer that was not.  This group would lose 2.5 points (.5 for the problem they correctly changed, 1 for the item that was initially incorrect that was never corrected, and 1 for the item that was correct initially but was changed later).
    • A group missed only 1 question on the first page.  After careful deliberation, the group cannot come to a consensus on which item is wrong and choose not to change any answers and get help from the teacher.  This group loses 1 point for the initial item that was incorrect.


9. Following the corrections, the teacher crosses out the initial number wrong and rewrites the final total wrong on that page.
10. After the students have either gotten all of the items correct on their first attempt or corrected their mistakes and earned a score, the students can move on to the second page.  Then, the groups follow the same pattern until they are completed with all four pages.
11. Students add up their score and write the number correct on the front of the packet with all of the students’ names on it.  This score can be used as an indicator of who won “the game,” or as a group grade.

The benefit of this activity occurs in group discussion both in coming to an initial consensus and in deciding which errors to correct.  Below is a group discussing their initial answers.


5 Closure - 5 minutes

Now that students have had multiple experiences dealing with chemical and physical reactions, ask the class to develop their own list of real world examples and classify them as chemical or physical.  On the front board or on chart paper, create a T chart with columns for "Chemical Reactions" and "Physical Reactions".  Have every student add one reaction that they see often in their own life and write it in the appropriate column before leaving class.