Conservation of mass in chemical reactions is the focus of this Grade 8 Science worksheet, where students investigate why the total mass remains constant in a closed system even when substances change into new products. Through a reading passage and targeted questions, students connect mass measurements, atom models, and chemical equations to explain how atoms are rearranged rather than created or destroyed during a reaction.

⚗️ Connect atoms, equations, and mass

The reading explains how scientists use evidence to account for matter before and after a chemical reaction. Students examine why a sealed container should have the same total mass before and after a reaction, then consider how atom models help track the atoms as they form new substances. The passage uses photosynthesis as an example, describing how carbon dioxide and water are rearranged to form glucose and oxygen.

A key concept is the difference between a closed system and an open system. When gas escapes from an uncovered container or another substance crosses the system boundary, the measured mass can change. Students learn to distinguish this change in measurement from a failure of conservation of mass by considering where matter can enter or leave the system.

What students practise

• Multiple-choice questions: identify the expected mass in a closed system, the role of atom models and chemical equations, and examples of matter leaving an open system.
• True-or-false statements: evaluate claims about atom rearrangement, mass measurements, and matter crossing a system boundary.
• Short written responses: explain why mass remains constant in a closed system and how atom models provide evidence.
• Matching and passage completion: connect key terms with their meanings and apply relevant vocabulary in context.
• Extended response: use a sealed-container investigation, an atom model, and a chemical equation to explain conservation of mass and compare the result with an open-container reaction.

📚 Resources included

• ✔️ Grade 8 student worksheet with a reading passage and written practice.
• ✔️ Separate PDF answer key for checking and reviewing responses.
• ✔️ Student Notes & Lesson Summary supplement for reinforcing the main concepts.
• ✔️ Separate teacher guide containing learning objectives, teaching tips, discussion questions, and common mistakes.

Use it for chemistry lessons and review

This conservation of mass worksheet can be used for classroom practice, independent work, lesson review, or an assessment of students' explanations of chemical change. The open-versus-closed-system examples are especially useful for discussing why a measured mass may decrease when gas escapes, even though matter is still conserved when the entire system is accounted for.

Within the stated Texas Science 8 topic of matter, water, and reactions under the TEKS framework, this resource helps students connect observable measurements to particle-level explanations. The included notes support student review, while the answer key and teacher guide provide separate materials for checking responses and preparing instruction.