Mass Stays the Same - Middle School Physical Science

Find the missing value using $m_{reactants} = m_{products}$ : reactants $= 50\,g$ , one product $= 18\,g$ .

$32\,g$ . $50\,g - 18\,g = 32\,g$ for the other product.
Find the correct claim: In a closed system, mass changes because atoms disappear. True or false?

False. Atoms cannot disappear; they only rearrange in reactions.
Which measurement best tests mass conservation in a closed-system lab model?

Total mass of the sealed container and contents before and after. Comparing total mass verifies conservation.
Identify the key evidence in a balance-scale model that shows mass is conserved.

The scale stays balanced before and after the change. Equal mass on both sides keeps the balance level.
Identify the correct conclusion if mass decreases only when the container is unsealed during reaction.

Matter escaped; the system became open, so measured mass decreased. Unsealing allows gas escape, converting closed to open system.
Find and correct the claim: "Mass is conserved because the number of molecules stays the same."

Correct: mass is conserved because the number of atoms stays the same. Molecules can change, but atom count must stay constant.
Which option best explains why mass can appear to increase in an open-system reaction?

A gas from the air enters and becomes part of the products. Gained mass indicates matter entered the system.
Identify the correct claim if a model shows the same atoms before and after but grouped differently.

Mass is conserved because the atoms are only rearranged. Same atoms = same total mass, just reorganized.
What is the correct conclusion if a sealed container has the same mass before and after heating?

Mass remained constant because the system was closed. No matter escaped, so mass stayed constant.
What is the law that states mass is conserved in a closed system?

Law of Conservation of Mass. This fundamental law states matter cannot be created or destroyed.
What is the correct interpretation if a model shows fewer atoms after a reaction in a sealed container?

The model is incorrect; atoms must be conserved. Models must show atom conservation to accurately represent reactions.
Which measurement provides direct evidence for mass conservation in a closed-container reaction?

Same total mass before and after the reaction. Equal mass measurements prove no matter was created or destroyed.
What law states that total mass stays constant in a closed system during a reaction?

Law of Conservation of Mass. Matter cannot be created or destroyed in chemical reactions.
Which change in a model indicates a chemical reaction occurred while conserving mass?

Bonds change and particles rearrange, but atom counts stay the same. New arrangements form new substances while preserving atom totals.
Choose the word that completes the claim: In a closed system, total mass is ____.

constant. Mass neither increases nor decreases in isolated systems.
Which boundary feature in a diagram indicates a closed system?

A sealed boundary with no arrows showing matter exchange. No arrows indicate no matter exchange with surroundings.
Identify the correct conclusion if the mass of a sealed flask increases after heating a substance.

A measurement error occurred; mass should stay constant in a closed system. True mass increase violates conservation; likely experimental error.
Which statement best describes mass during a chemical reaction in a closed system?

Total mass of reactants equals total mass of products. Mass is conserved because atoms only rearrange, not disappear.
Which statement best completes the claim: In a closed system, the mass of reactants ___ the mass of products?

equals. Mass is conserved, so reactant mass = product mass.
What must be true about the number of each atom type in reactants and products for mass conservation?

Each atom type count must match before and after the reaction. Same atom inventory ensures same total mass by conservation law.
Which option best explains why mass can appear to decrease in an open-container reaction?

Gas products escape, so measured mass of the container decreases. Escaping gas removes mass from the measured system.
Which option is the correct justification from a model when a precipitate forms in a sealed bag?

Total mass stays the same; particles changed arrangement, not amount. Sealed bag = closed system, so mass is conserved.
What is an open system in the context of conserving mass?

A system where matter can enter or leave the boundary. Matter can cross the boundary, allowing mass changes.
What is the main difference between an open system and a closed system for mass evidence?

Open: matter can leave or enter; closed: matter cannot. The key distinction is whether matter can cross system boundaries.
Identify the correct conclusion if a model shows atoms leaving the boundary during a reaction.

The system is open, so measured mass of the system can change. Matter leaving means it's not truly closed.
What is the best conclusion if a sealed bag has the same mass before and after a reaction?

Mass was conserved because the system was closed. No mass change confirms the system remained properly sealed.
Find the missing value using $m_{reactants} = m_{products}$ : products total $= 120\,g$ , one reactant $= 45\,g$ .

$75\,g$ . $120\,g - 45\,g = 75\,g$ for the other reactant.
Which option is the correct interpretation of particle models for a closed system reaction?

Particles rearrange; the total number of atoms stays the same. Atoms only change bonds, not quantity.
What is a closed system in the context of conserving mass?

A system where no matter enters or leaves the boundary. Matter cannot cross the boundary, keeping total mass constant.
Which option best explains why mass can appear to decrease in an open-system reaction?

A gas product escapes to the surroundings. Lost mass indicates matter left the system.
What is the correct evidence-based claim if a sealed container forms a gas but mass is unchanged?

The gas stayed in the container, so total mass was conserved. Sealed container prevents gas escape, maintaining total mass.
What is the equation that represents conservation of mass in a closed system?

$m_{reactants} = m_{products}$ . Mathematical representation of mass conservation.
Identify the key model-based idea that explains why mass stays constant in a closed system.

Atoms are rearranged, not created or destroyed. Chemical reactions only reorganize existing atoms into new molecules.
Which option is the best reason a balance reading stays the same for a sealed reaction setup?

No matter leaves or enters, so total mass remains the same. Sealed containers prevent matter exchange with surroundings.
What must be counted in a particle model to justify mass conservation during a reaction?

The number of each type of atom on both sides. Equal atom counts prove mass conservation.
What must be included in a particle model to justify mass conservation during a reaction?

Same number of each type of atom before and after. Conservation requires all atoms present initially remain after reaction.
Identify what a balanced chemical equation represents about atoms and mass in a closed system.

Equal atoms on both sides, supporting equal total mass. Balanced equations show atom conservation, proving mass conservation.
What is the definition of a closed system in terms of matter and mass?

A system where no matter enters or leaves; total mass stays inside. Matter cannot cross the system boundary, preserving total mass.
What does it mean to say atoms are conserved in a chemical reaction model?

Atoms are not created or destroyed; they are rearranged. Chemical reactions only reorganize existing atoms.

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