Conservation in Reactions Lesson Plan (TEKS 8.6E): A Complete 5E Lesson for the Law of Conservation of Mass

Inside the Conservation in Reactions 5E Lesson

The 5E instructional model walks students through five phases: Engage, Explore, Explain, Elaborate, and Evaluate. It flips the traditional lecture-first sequence on its head. Students explore a concept hands-on before you ever explain it, which means by the time you do explain it, they have something to hook the vocabulary onto.

I switched to the 5E model years ago and stopped going back. Kids retain more, ask better questions, and stop staring at me waiting to be told the answer. The Conservation in Reactions 5E Lesson is built on this framework from start to finish. Here's how it plays out across the five phases.

🎯 Engage

Day one is a teacher-led sealed bag investigation. Each student (or small group) gets a zip-top bag with a small cup of vinegar inside and a measured amount of baking soda in the corner. Students mass the sealed bag before anything mixes, then tip the bag so the baking soda falls into the vinegar. The reaction takes off, the bag puffs up with carbon dioxide, and the mass on the scale stays exactly the same.

Then they open the bag, let the gas out, and mass it again. Now it's lighter. The atoms didn't disappear, they just floated away as gas. By the end of the period, students have observed the law of conservation of mass with their own eyes, and they have a working answer to the question "where did the mass go when we opened the bag?" Nobody has heard a vocabulary lecture yet. That's the point.

What's included in the Engage:

• Teacher directions for the sealed bag baking soda and vinegar investigation
• Printable student observation sheet with mass before, mass after, and mass after opening
• Answer key for the discussion questions
• Four learning objective slides (standard verbatim, the "investigate and relate" verb highlighted, "I CAN...", and "WE WILL...")
• An illustrated Chemistry Word Wall in English and Spanish covering the full unit vocabulary

🔬 Explore

The Conservation in Reactions Station Lab is the heart of the Explore phase. Students rotate through 8 stations (plus a 9th challenge station for early finishers) over one class period. The Station Lab is split into four input stations (where kids take in new information) and four output stations (where they show what they learned).

The four input stations:

• 🎬 Watch It! — Students watch a short video on the law of conservation of mass and balanced equations, then answer guided questions.
• 📖 Read It! — A one-page reading passage at two differentiated levels on how atoms rearrange during a chemical reaction and how balanced equations prove conservation, with a Spanish version included.
• 🔬 Explore It! — The hands-on activity (the heart of the Station Lab) where students count atoms on the reactants and products sides of a set of chemical equations and verify whether each is balanced.
• 💻 Research It! — Reference cards with the law of conservation of mass, the difference between subscripts and coefficients, and Antoine Lavoisier's sealed-jar experiments.

The four output stations:

• 📋 Organize It! — A card sort where students physically place reactants and products from a reaction on either side of an arrow and verify the atom counts match.
• 🎨 Illustrate It! — Students draw a labeled balanced equation with atom diagrams on each side to prove conservation.
• ✍️ Write It! — Three open-ended questions in complete sentences on why mass appears to change in an open container and how a balanced equation proves conservation.
• 📝 Assess It! — A short formative check with multiple choice and a fill-in-the-blank vocabulary paragraph.

Print and digital versions are both included. If you want the full breakdown of what happens at every single station, what students produce, and how to set it up, that's in our dedicated Station Lab post.

→ Read the full Conservation in Reactions Station Lab walkthrough 8 stations, materials list, teacher tips

The Station Lab is included in the full 5E lesson. You don't need to buy it separately if you're getting the whole unit.

📚 Explain

Here's the real payoff of doing the Engage and Explore before the Explain: by the time kids hit this phase, they've already watched mass stay the same in a sealed bag and counted atoms on both sides of a chemical equation. They have a working understanding before you ever start defining things. The discussions get deeper, the questions get sharper, and you spend less time defining and more time pushing their thinking.

The Conservation in Reactions Presentation walks 8th graders through the full scope of TEKS 8.6E, one concept at a time, with atom-count diagrams on nearly every slide. The deck opens with a reset on matter (anything that has mass and takes up space, made of atoms with protons, neutrons, and electrons), then defines a chemical reaction as a process that involves the rearrangement of atoms. The big idea (matter is neither created nor destroyed) is introduced through Antoine Lavoisier's late-1700s sealed-jar experiments, which became the foundation of the Law of Conservation of Mass.

Students learn how to count atoms in a formula using subscripts (the small numbers written after an element symbol, telling you how many atoms of that element are in one molecule) and coefficients (the big numbers written in front of a formula, telling you how many molecules you have). H2O has two hydrogen atoms and one oxygen atom. 2H2O has four hydrogen atoms and two oxygen atoms, for a total of six. 3H2O has six hydrogens and three oxygens, for a total of nine. The deck pushes this until students can multiply coefficients by subscripts on autopilot.

From there, the Presentation moves into chemical equations with their three parts: the reactants (initial substances on the left of the arrow), the products (new substances on the right), and the arrow that represents the reaction. Students apply conservation to real reactions: Na + Cl going to NaCl (100 g of sodium plus 100 g of chlorine equals 200 g of table salt), methane combustion (16 g of CH4 plus 64 g of O2 equals 80 g of CO2 plus H2O on the product side), and the baking soda and vinegar reaction in a sealed system (20 g of NaHCO3 plus 200 g of vinegar still equals 220 g, even with all the bubbles). The unit closes on photosynthesis, the standard's named example: 6CO2 + 6H2O + light energy goes to C6H12O6 + 6O2. Students count the carbons, hydrogens, and oxygens on each side and prove the equation balances.

For every reaction, students see the same three-step process: count atoms on the reactants side, count atoms on the products side, confirm they match. That repetition (different reactions, same conservation check) bakes the "investigate how mass is conserved and relate to the rearrangement of atoms" verb of TEKS 8.6E into long-term memory.

What makes the Conservation in Reactions Presentation different from a typical chemistry slideshow is that kids are doing something on almost every single slide. It's not a lecture deck. It's a participation deck. "Your answer:" prompts appear on most slides, Brain Breaks reset attention every few slides (predict the mass after a baking soda and vinegar reaction in a closed system), Quick Action INB tasks (count atoms in compounds, balance a methane combustion reaction on a digital scale, label equations as equal or unequal mass) show up throughout, and Think About It prompts push deeper into bigger ideas like why an antacid reaction in an open container loses mass and how the slow carbon cycle illustrates conservation of mass over geologic time. The deck closes with a Check for Understanding tied back to the two Essential Questions: How is mass conserved in chemical reactions? and How can you relate the conservation of mass to the rearrangement of atoms using chemical equations?

The Explain materials in this product include:

• An editable 28-slide Presentation at two differentiated levels (Dependent and Modified), works in PowerPoint or Google Slides
• A guided fill-in-the-blank student notes handout that mirrors the Presentation, with answer key
• A Paper Interactive Notebook (English and Spanish) students cut, fold, and glue into their notebooks
• A Digital Interactive Notebook at both levels with answer keys, for 1:1 classrooms or Google Classroom

The Explain runs across two class periods. The built-in Think About It prompts are where the real discussion happens, so let those breathe.

🛠️ Elaborate

The Elaborate phase is where students stretch what they learned about conservation of mass and balanced equations and put it into a project of their choosing. In this 8th grade chemistry lesson, that's a Student Choice Project board with six different project options plus a "design your own" pathway.

Students might build a 3D atom-bead model of the photosynthesis equation that shows the same six carbons, twelve hydrogens, and eighteen oxygens on each side of the arrow, or design a wanted poster for the "missing" mass in an open-container reaction (with the carbon dioxide gas as the suspect), or write a short courtroom skit where Antoine Lavoisier defends conservation of mass against the prosecution. There are options for kids who love to write, kids who love to draw, kids who love to build, and kids who love to perform. Whatever the project, the point is the same: students apply the law of conservation of mass and the rearrangement of atoms in balanced equations to a real-world artifact instead of a worksheet.

Choice is the whole point. By letting students pick how they show their thinking, you get more authentic work for TEKS 8.6E and you actually get to see what they understand about conservation of mass.

The rubric (the part teachers actually want)

Every project, no matter which option a student picks, is graded on the same 100-point rubric. Five categories at 20 points each:

• Vocabulary (20 pts) — At least four words from the lesson are used in context.
• Concepts (20 pts) — At least two key concepts from the lesson are referenced.
• Presentation (20 pts) — The project grabs attention and is well-organized.
• Clarity (20 pts) — Easy to understand. Free of typos.
• Accuracy (20 pts) — Drawings and models are accurate. The science is right.

Two differentiated versions in one file

The standard version is for students ready for independent application. The Reinforcement version is for students who need additional vocabulary or concept support. Three of the six options are swapped for projects with a tighter vocabulary tie-in, and "design your own" is replaced with "collaborate with the teacher" so kids aren't pitching cold.

✅ Evaluate

The Evaluate phase wraps the unit with a formal assessment. It's not all bubble-in. Several questions hand students a chemical equation and ask them to count atoms on each side, determine if the equation is balanced, and explain how it demonstrates conservation of mass.

The full assessment has 12 questions across five formats:

• Multiple choice (4 questions) covering the law of conservation of mass, subscripts vs. coefficients, reactants vs. products, and the photosynthesis equation
• Hotspot / visual (2 questions) where students circle the balanced equation and identify the missing coefficient that would balance a given reaction
• Multiselect (2 questions) where students pick all the statements that correctly describe conservation of mass in a chemical reaction
• Short answer (2 questions) on why mass appears to decrease in an open container and how a balanced equation proves no atoms were created or destroyed
• Multipart scenario (2 questions) with a 3-student classroom debate where kids identify which student's reasoning correctly explains a closed-system reaction

A modified version is included for students who need additional support, with fewer multiple-choice distractors and sentence-starter scaffolds on the short-answer items.

If you've taught all five phases, this assessment shouldn't surprise anyone. It's a chance for kids to show you they get it.