8.6dc

Analyze the chemical reaction between lead nitrate and sodium iodide modeled by this chemical equation.

Pb(NO₃)₂(aq) + 2NaI(aq) → PbI₂(s) + 2NaNO₃(aq)

Which characteristics of the reactants and products are the same and which are different? Move each answer to the correct box.

Groups:

(a) Same for reactants and products

,

(b) Different for reactants and products

• number of O atoms

• physical properties of the substances

• number of N atoms

• chemical properties of the substances

An iron (Fe) nail is exposed to oxygen (O₂) in the air. Rust (Fe₂O₃) forms on the nail. This process is modeled by this chemical equation:

4Fe + 3O₂ → 2Fe₂O₃

What process is taking place, and what happens to the mass of the nail after rusting?

• This is a physical change because the rust can be scraped off, leaving the nail with the same mass as before the rust formed.

• This is a chemical reaction but mass is not conserved because the mass of the nail and the rust is greater than the mass of the nail.

• This is a chemical reaction and mass is conserved because the mass of the iron and oxygen nail and the rust is equal to the mass of  iron plus the oxygen in the rust that formed.

• This is a physical change because mass is not conserved since the nail and the rust have more mass than the nail before the rust formed.

Emily helped her friend make pizza. They flattened dough on a baking sheet, spread sauce on the dough, and sprinkled cheese on top. They put the pizza in the hot oven. The crust rose, became thicker, turned brown, and the cheese melted.

How can the pizza making be analyzed to identify chemical and physical changes?

Move ONE correct answer to each box. Not all answers will be used.

a

b

D

C

A

B

A chemical reaction is a type of system. During photosynthesis, water (H₂O) and carbon dioxide (CO₂) along with energy from sunlight react to form oxygen (O₂) and glucose (C₆H₁₂O₆). This process is modeled as shown.

6H₂O +  6CO₂ → 6O₂ + C₆H₁₂O₆

What type of change is occurring, and what happens with the mass of the system?

• This is a physical change, and the mass of the system remains constant.

• This is a chemical change, and the mass of the system remains constant.

• This is a physical change, and the mass of the system increases as the change occurs.

• This is a chemical change, and the mass of the system increases as the change occurs.

When hydrogen gas (H₂) reacts with oxygen gas (O₂), water vapor (H₂O) forms in the balanced chemical equation shown.

2H₂ + O₂ → 2H₂O

How can the balanced chemical equation be modeled using the correct number of molecules?

Move each answer to the correct box. Each answer may be used more than once.

Groups:

(a) Reactant(s)

,

(b) Product(s)

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• 
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