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7.77 Evidence of Chemical Reactions and Conservation of Atoms Worksheet

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Worksheet Overview & Skills Covered

Core academic competencies and curriculum alignment

This Grade 7 Science worksheet provides structured practice on 7.77 Evidence of Chemical Reactions and Conservation of Atoms. Students are guided through targeted exercises that build foundational understanding, computational accuracy, and critical thinking skills.

Evidence of Chemical Reactions and Conservation of Atoms - Which observation best supports that a chemical reaction occurred while conserving atoms? (NGSS MS‑PS1‑2, MS‑PS1‑5)

Whether you are an educator preparing classroom handouts, a tutor reinforcing weekly topics, or a parent supporting homeschool learning, this printable resource gives students the deliberate practice required to achieve subject fluency and master state standards.

Grade

Grade 7

Subject

Science

Domain

Science Curriculum

Formats

PDF & DOCX

Sample Practice Problems

Preview the types of problems and questions covered in this worksheet

Below are sample questions representative of the exercises included on this worksheet and related 7.77 Evidence of Chemical Reactions and Conservation of Atoms skill assessments:

Problem 1Difficulty: Mastery

In an open reaction, the mass on the balance drops from 55.0 g to 53.5 g while bubbling occurs. A student repeats the reaction in a sealed bag and the mass stays 55.0 g. |

Which statement best uses these results to connect evidence of reaction and conservation?

AThe mass drop in the open trial proves atoms were destroyed.

BThe bubbling shows a reaction produces a gas; the open trial lost gas to the air, but the sealed trial kept all atoms in the measured system, so its constant mass supports conservation.

CThe open trial proves conservation is false, and the sealed trial proves it is true.

DThe sealed trial proves no reaction happened because the mass stayed the same.

Solution & Explanation:The difference comes from the system boundary. In open air, gas can escape, lowering the measured mass. In a sealed bag, products can't leave, so mass stays constant-supporting conservation of atoms while still allowing a chemical reaction.

Problem 2Difficulty: Mastery

A sealed reaction produces both a precipitate and a gas bubble pocket. The mass of the sealed container stays constant, but the mixture looks very different. |

Which statement is best supported by these observations?

AA chemical reaction occurred (new solid and gas formed) and atoms were conserved in the sealed system (constant total mass).

BNo reaction occurred because mass stayed constant.

CConservation means you cannot form new substances.

DAtoms were destroyed because the appearance changed.

Solution & Explanation:New solid and gas indicate new substances formed-evidence of a chemical reaction. In a sealed container, constant mass supports conservation of atoms: matter stayed in the system and was rearranged.

Problem 3Difficulty: Mastery

A student wants one observation that best supports 'reaction + conservation' in a real lab. |

Which observation is the BEST choice?

AThe container is sealed, so conservation is automatic even if you don't measure anything.

BThe mixture is stirred and looks more evenly mixed.

CThe mass of the remaining solid decreases in an open container.

DA gas forms in a sealed container and the total mass of the sealed container stays the same before and after.

Solution & Explanation:Gas formation is strong evidence of a chemical reaction. To support conservation, you need a closed system and a measurement showing mass is unchanged for that system. Open-container mass changes don't directly test conservation.

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QWhat grade level and standards does this worksheet align with?

This worksheet is designed specifically for Grade 7 Science students. It aligns with educational standard SCI.7.77 (Grade 7 science practice focused on evidence of chemical reactions and conservation of atoms.).