Question

use the information below to answer questions 7 - 8.

1. the diagram above represents solid carbon dioxide, better known as dry ice. which diagram below best represents some of the dry ice after it sublimes into a gas?
2. justify your selection in #7,

(a) sublimation is a chemical change, so the co₂ molecules should rearrange into individual atoms.
(b) sublimation is a physical change, so the co₂ molecules should remain in the same composition.
(c) sublimation is a chemical change, so the co₂ molecules should rearrange into different molecules.
(d) sublimation is a physical change, so the co₂ molecules should rearrange into compounds with different properties.

Explanation:

Question 7

Step1: Understand the nature of sublimation

Sublimation is a physical change. In a physical change, the chemical composition of the substance remains the same. Dry - ice (\(CO_2\)) subliming means it changes from solid to gas. The \(CO_2\) molecules in the gas phase should still be \(CO_2\) molecules (not broken into atoms or different molecules).

Step2: Analyze each option

• Option (A): Shows \(CO_2\) molecules. Since sublimation is a physical change and \(CO_2\) molecules remain as \(CO_2\) molecules in the gas phase, this is a candidate.
• Option (B): Shows separated atoms (black and white circles are not in the \(CO_2\) molecular form (\(O - C - O\))). Sublimation is a physical change, and molecules do not break into atoms, so this is incorrect.
• Option (C): Shows separated atoms (black and white circles are not in the \(CO_2\) molecular form (\(O - C - O\))). Sublimation is a physical change, and molecules do not break into atoms, so this is incorrect.
• Option (D): Has a mix of different - looking molecular - like structures. Sublimation is a physical change, and the molecules should remain as \(CO_2\) molecules, so this is incorrect.

Question 8

Step1: Recall the definition of physical and chemical change

A physical change is a change in the state (solid, liquid, gas) or appearance of a substance without changing its chemical composition. A chemical change involves a change in the chemical composition (new substances are formed).

Step2: Analyze each option

• Option (A): Sublimation is a physical change, not a chemical change. So, the statement “Sublimation is a chemical change” is wrong.
• Option (B): Sublimation is a physical change. In a physical change, the chemical composition of the substance (\(CO_2\) in this case) remains the same. The \(CO_2\) molecules do not break into atoms or form new substances.
• Option (C): Sublimation is a physical change, not a chemical change. So, the statement “Sublimation is a chemical change” is wrong.
• Option (D): In a physical change (sublimation), the properties related to the chemical composition (since the composition doesn't change) do not change. The molecules remain as \(CO_2\) molecules.

Answer:

Question 7

A.

Question 8

B.