Problem 34 - Chemistry and Chemical Reactivity

Question

Eight observations are listed below. Which of these observations identify chemical properties? (a) Sugar is soluble in water. (b) Water boils at \(100^{\circ} \mathrm{C}\) (c) Ultraviolet light converts \(\mathrm{O}_{3}\) (ozone) to \(\mathrm{O}_{2}\) (oxygen). (d) Ice is less dense than water. (e) Sodium metal reacts violently with water. (f) \(\mathrm{CO}_{2}\) does not support combustion. (g) Chlorine is a yellow gas. (h) Heat is required to melt ice.

Step-by-Step Solution

Answer

Chemical properties: (c), (e), (f).

Step 1: Understand Chemical Properties

Chemical properties describe how a substance interacts with other substances and undergoes chemical changes. They often involve a change in the composition of the substance and can result in the formation of one or more new substances.

Step 2: Analyze Each Observation

Go through each observation and determine if it represents a chemical property based on the definition from Step 1.

Step 3: Evaluate Observation (a)

(a) Sugar is soluble in water. This is a physical property because it involves sugar dissolving in water without changing the chemical composition of sugar.

Step 4: Evaluate Observation (b)

(b) Water boils at \(100^{\circ}C\). This is a physical property because it describes a phase change without a change in chemical composition.

Step 5: Evaluate Observation (c)

(c) Ultraviolet light converts \(\mathrm{O}_{3}\) (ozone) to \(\mathrm{O}_{2}\) (oxygen). This is a chemical property because it describes a chemical reaction where the chemical composition changes from ozone to oxygen.

Step 6: Evaluate Observation (d)

(d) Ice is less dense than water. This is a physical property because it pertains to the density of a substance, a physical characteristic.

Step 7: Evaluate Observation (e)

(e) Sodium metal reacts violently with water. This is a chemical property because it describes a chemical reaction where new substances are formed.

Step 8: Evaluate Observation (f)

(f) \(\mathrm{CO}_{2}\) does not support combustion. This is a chemical property because it describes the inability of \(\mathrm{CO}_{2}\) to undergo a reaction (combustion).

Step 9: Evaluate Observation (g)

(g) Chlorine is a yellow gas. This is a physical property as it describes the color and state of the substance without changing the chemical composition.

Step 10: Evaluate Observation (h)

(h) Heat is required to melt ice. This is a physical property as it refers to a phase change from solid to liquid, without altering the chemical identity.

Key Concepts

chemical changes

Chemical changes occur when a substance is transformed into one or more new substances with different chemical compositions and properties. These changes usually involve chemical reactions where bonds are broken and new ones are formed. Chemical changes are typically irreversible under normal conditions. Example indicators include:

• Change in color
• Formation of a precipitate
• Release or absorption of energy
• Formation of gas
• Odor change

An understanding of how substances change at a molecular level helps in identifying chemical properties. For instance, converting ozone ( ext{O}_{3}) to oxygen ( ext{O}_{2}) using ultraviolet light is a chemical change because the molecular structure undergoes a transformation, altering its properties.

substance interactions

Substance interactions refer to the way different chemicals or materials affect each other, often leading to a chemical reaction. Through these interactions, new products with distinct properties from the original materials may form. Such interactions are central to various everyday processes, from digestion in our bodies to industrial manufacturing. When sodium metal reacts violently with water, it demonstrates a specific interaction that results in the production of hydrogen gas and sodium hydroxide. This is not just a chemical property of sodium itself, but how it specifically interacts with water. Understanding the dynamics of substance interactions allows chemists to predict and manipulate reactions for desired outcomes.

physical properties

Physical properties are characteristics that can be observed or measured without changing the substance's chemical identity. They include aspects like state of matter, color, density, boiling point, melting point, and solubility. These properties aid in the classification and identification of substances.For instance, the solubility of sugar in water is a physical property because the sugar molecules disperse in the water without a change in their chemical structure. Similarly, water boiling at \(100^{\circ}C\) is another physical property that describes a change in state. These properties are easily reversible under the right conditions, such as refreezing water to make ice.

chemical reactions

Chemical reactions involve the reorganization of atoms, resulting in new substances with different properties. These processes are fundamental to both organic and inorganic chemistry and are represented by chemical equations. Chemical reactions can be classified into various types such as synthesis, decomposition, single replacement, double replacement, and combustion. In the context of combustion, ext{CO}_{2} not supporting combustion signifies a chemical property. This indicates that carbon dioxide cannot act as a combusting agent in a reaction. Each reaction type has its own specific conditions and predicts the possible outcomes of mixing certain reactants. Recognizing these reactions allows us to harness chemical changes for practical applications like energy production and material synthesis.