Chemistry — Chapter review · Physical Science: Matter, Forces & Energy, Grade 8

They can rule out alternative explanations. Composition evidence together with controlled changes is stronger than relying on one ambiguous sign.

They can rule out alternative explanations. Composition evidence together with controlled changes is stronger than relying on one ambiguous sign.

Response criteria

• Use the supplied conditions and relevant evidence.
• Explain the scientific mechanism or calculation.
• State a meaningful limitation or testable next step.

Bubbles appearing is the observation; the proposed origin is an inference until supported by identity and other evidence.

Bubbles appearing is the observation; the proposed origin is an inference until supported by identity and other evidence.

Response criteria

• Use the supplied conditions and relevant evidence.
• Explain the scientific mechanism or calculation.
• State a meaningful limitation or testable next step.

Use the illustrated study titled Chemical interactions in daily life and history. Keep the observations, model and conditions separate.

Cutting can retain iron identity while rust formation produces different substances. An alloy can be a mixture rather than one fixed-ratio compound. Chemical risk cannot be decided from the word alone; identity, amount, exposure and use need evidence. Relate the chosen process to a practical effect while keeping ordinary atom rearrangement distinct from nuclear element formation.

Cutting can retain iron identity while rust formation produces different substances. An alloy can be a mixture rather than one fixed-ratio compound. Chemical risk cannot be decided from the word alone; identity, amount, exposure and use need evidence. Relate the chosen process to a practical effect while keeping ordinary atom rearrangement distinct from nuclear element formation.

Response criteria

• Distinguish composition from appearance.
• Explain a daily/historical consequence with a mechanism.
• Evaluate blanket chemical/mixture claims with conditions.

Bubbles are observed; a new chemical substance is not yet established. Obtain appropriate supplied gas-identity or characteristic-property evidence and compare the control/conditions.

Record appearance without assigning an unsupported identity.

Use a discriminating comparison rather than one visual sign.

Bubbles are observed; a new chemical substance is not yet established. Obtain appropriate supplied gas-identity or characteristic-property evidence and compare the control/conditions.

Response criteria

• Use the named labels, directions or supplied quantities accurately.
• Connect the visual evidence to the scientific mechanism or calculation.
• State the relevant model conditions or limitation.

A reaction can regroup the same atoms into a different number of molecules. Each element count, and total mass for the closed ordinary-reaction system, remains conserved.

A reaction can regroup the same atoms into a different number of molecules. Each element count, and total mass for the closed ordinary-reaction system, remains conserved.

Response criteria

• Use the supplied conditions and relevant evidence.
• Explain the scientific mechanism or calculation.
• State a meaningful limitation or testable next step.

1.5 g, if escaping gas is the supported explanation and measurements are comparable.

1.5 g, if escaping gas is the supported explanation and measurements are comparable.

Response criteria

• Use the supplied conditions and relevant evidence.
• Explain the scientific mechanism or calculation.
• State a meaningful limitation or testable next step.

5 g of incoming gas, so 9+5 = 14 g. The increase concerns matter crossing the measured boundary rather than matter being created.

Subtract the initial solid mass from product mass.

Identify the initially omitted matter source.

5 g of incoming gas, so 9+5 = 14 g. The increase concerns matter crossing the measured boundary rather than matter being created.

Response criteria

• Use the named labels, directions or supplied quantities accurately.
• Connect the visual evidence to the scientific mechanism or calculation.
• State the relevant model conditions or limitation.

A coefficient multiplies every atom in that formula. Fixing one element can change another element count and require an additional adjustment.

A coefficient multiplies every atom in that formula. Fixing one element can change another element count and require an additional adjustment.

Response criteria

• Use the supplied conditions and relevant evidence.
• Explain the scientific mechanism or calculation.
• State a meaningful limitation or testable next step.

It names a different substance with different composition. Use whole-particle coefficients to balance the intended water reaction.

It names a different substance with different composition. Use whole-particle coefficients to balance the intended water reaction.

Response criteria

• Use the supplied conditions and relevant evidence.
• Explain the scientific mechanism or calculation.
• State a meaningful limitation or testable next step.

N₂ + 3H₂ → 2NH₃. Both sides contain 2 N atoms and 6 H atoms.

Match two nitrogen atoms using 2NH₃.

That product count needs six H atoms, supplied by 3H₂.

N₂ + 3H₂ → 2NH₃. Both sides contain 2 N atoms and 6 H atoms.

Response criteria

• Use the named labels, directions or supplied quantities accurately.
• Connect the visual evidence to the scientific mechanism or calculation.
• State the relevant model conditions or limitation.

Energy released during formation of new bonds can exceed the energy required to break starting bonds. The difference is the overall release.

Energy released during formation of new bonds can exceed the energy required to break starting bonds. The difference is the overall release.

Response criteria

• Use the supplied conditions and relevant evidence.
• Explain the scientific mechanism or calculation.
• State a meaningful limitation or testable next step.

The reaction would require a net 30 units from surroundings under that model, making the net process endothermic.

The reaction would require a net 30 units from surroundings under that model, making the net process endothermic.

Response criteria

• Use the supplied conditions and relevant evidence.
• Explain the scientific mechanism or calculation.
• State a meaningful limitation or testable next step.

Use the illustrated study titled Design a chemical thermal device. Keep the observations, model and conditions separate.

A qualifies at 32 °C under the stated 40 °C maximum, while B’s 45 °C violates it despite longer duration. A revision could improve insulation or transfer geometry within the reagent limit, then retest target temperature over time and check containment. Supplied C records at 35 °C for 12 minutes support that simulated comparison; they do not substitute for actual construction evidence. Account for reaction, target and surrounding energy pathways. For a real cooler route, vinegar/bicarbonate interaction can lower the reaction-mixture temperature; target water can then transfer energy through the inner-cup wall. Record the target separately and compare repeated A/B curves with a no-reaction reference. Geometry and environmental exchange can obscure a small effect, so no precise decrease is promised. A model or example result is not a substitute for actual target readings.

A qualifies at 32 °C under the stated 40 °C maximum, while B’s 45 °C violates it despite longer duration. A revision could improve insulation or transfer geometry within the reagent limit, then retest target temperature over time and check containment. Supplied C records at 35 °C for 12 minutes support that simulated comparison; they do not substitute for actual construction evidence. Account for reaction, target and surrounding energy pathways. For a real cooler route, vinegar/bicarbonate interaction can lower the reaction-mixture temperature; target water can then transfer energy through the inner-cup wall. Record the target separately and compare repeated A/B curves with a no-reaction reference. Geometry and environmental exchange can obscure a small effect, so no precise decrease is promised. A model or example result is not a substitute for actual target readings.

Response criteria

• Apply criteria and hard constraints.
• Explain reaction energy, separate target/mixture readings and open containment.
• Compare original/revised trial evidence and its limits.

Net 25 units enter from surroundings under this model, so the overall reaction is endothermic. Forming bonds releases 55; breaking them requires 80.

Compare the two contributions with directions stated.

Classify the net result, not an isolated bond step.

Net 25 units enter from surroundings under this model, so the overall reaction is endothermic. Forming bonds releases 55; breaking them requires 80.

Response criteria

• Use the named labels, directions or supplied quantities accurately.
• Connect the visual evidence to the scientific mechanism or calculation.
• State the relevant model conditions or limitation.

pH 4 corresponds to about 100 times the hydrogen-ion concentration of pH 6. The two-unit difference represents two factors of ten.

pH 4 corresponds to about 100 times the hydrogen-ion concentration of pH 6. The two-unit difference represents two factors of ten.

Response criteria

• Use the supplied conditions and relevant evidence.
• Explain the scientific mechanism or calculation.
• State a meaningful limitation or testable next step.

No. Neutrality does not rule out harmful dissolved substances or microorganisms. Safety requires separate evidence.

No. Neutrality does not rule out harmful dissolved substances or microorganisms. Safety requires separate evidence.

Response criteria

• Use the supplied conditions and relevant evidence.
• Explain the scientific mechanism or calculation.
• State a meaningful limitation or testable next step.

The 8–9 sample is basic and the pH 6 sample acidic under the stated common room-temperature aqueous convention. Indicator color supplies a range, not that exact decimal.

Use the supplied key and conditions.

Respect measurement resolution and the logarithmic scale.

The 8–9 sample is basic and the pH 6 sample acidic under the stated common room-temperature aqueous convention. Indicator color supplies a range, not that exact decimal.

Response criteria

• Use the named labels, directions or supplied quantities accurately.
• Connect the visual evidence to the scientific mechanism or calculation.
• State the relevant model conditions or limitation.