Problem 25 - Chemistry Principles and Practice

Question

Each of the following parts contains an underlined property. Classify the property as intensive or extensive and as chemical or physical. (a) Bromine is a reddish liquid. (b) A ball is a spherical object. (c) Sodium and chlorine react to form table salt. (d) A sample of water has a \(\underline{\text { mass of } 45 \mathrm{~g} \text { . }}\) (e) The density of aluminum is \(\underline{2.70 \mathrm{~g} / \mathrm{cm}^{3} \text { . }}\)

Step-by-Step Solution

Answer

(a) Intensive, Physical; (b) Intensive, Physical; (c) Chemical; (d) Extensive, Physical; (e) Intensive, Physical.

Step 1: Classify Bromine Property

The property given is that bromine is a reddish liquid. Color is a property that doesn't depend on the quantity of the substance, making it an intensive property. It's a physical property since it describes the appearance of bromine without changing its chemical structure.

Step 2: Classify Ball Property

The property is that a ball is a spherical object. The shape of an object is an intensive property because it does not depend on the quantity of material. It is a physical property because it describes the shape without altering the chemical composition.

Step 3: Classify Sodium-Chlorine Reaction

The property discussed here is that sodium and chlorine react to form table salt. This involves a chemical reaction, indicating it's a chemical property. It describes the ability of sodium and chlorine to undergo a transformation to form a new substance.

Step 4: Classify Water Mass Property

The underlined property is mass, specifically that a sample has a mass of 45 g. Mass depends on the amount of substance, making it an extensive property. It is a physical property because it doesn't involve a change in the substance's chemical structure.

Step 5: Classify Aluminum Density Property

The property is that aluminum has a density of 2.70 g/cm³. Density is independent of the amount of the substance, classifying it as an intensive property. Since density relates to the substance's makeup without changing it, it is also a physical property.

Key Concepts

Chemical Properties

Chemical properties are characteristics of a substance that become evident during or after a chemical reaction. They describe the potential of a substance to undergo a transformation and form new substances. This is unlike physical properties, which do not involve changing the composition or identity of a substance.

• Examples of chemical properties include reactivity with other chemicals, flammability, and pH levels.
• Sodium's ability to react with chlorine to form table salt is a prime example of a chemical property. It illustrates how sodium can chemically change to create a new compound.

Chemical properties are crucial in understanding how elements interact and transform. They are indicators of the chemical changes a substance can undergo, which often involve the breaking and forming of chemical bonds.

Physical Properties

Physical properties are attributes of a substance that can be observed or measured without changing the substance's chemical identity. These properties provide insights into the substance's physical characteristics without altering its composition.

• Common physical properties include color, density, mass, volume, and state of matter (solid, liquid, gas).
• For instance, aluminum's density of 2.70 g/cm³ and bromine being a reddish liquid are physical properties. These describe the material’s appearance and density without altering what the substance is chemically.

Physical properties are crucial in identifying and classifying substances. They help determine how a substance can be used or how it behaves in different conditions without involving a chemical change.

Classification of Matter

The classification of matter involves categorizing substances based on their properties and behaviors. Matter can generally be classified into pure substances (elements and compounds) and mixtures (homogeneous and heterogeneous).

• Pure substances have uniform and definite compositions, like elements such as gold or compounds like water.
• Mixtures are combinations of two or more substances, such as saltwater or air, where each substance holds its original properties.

Within these classifications, properties of substances are used to further distinguish them. For example, intensive properties (like color and density) do not depend on the amount of matter, whereas extensive properties (like mass and volume) do. Understanding how to classify matter is foundational in studying and applying chemistry, as it impacts how substances are manipulated and utilized.

Properties of Elements

Elements have distinct properties that help in identifying and distinguishing them from one another. Each element's properties can be classified as either physical or chemical.

• Physical properties might include boiling and melting points, color, and state at room temperature.
• Chemical properties involve how an element reacts with others, such as oxygen or acids, and its place in the periodic table.

For example, bromine is notable for being a reddish liquid at room temperature, a rare physical property among elements. Such properties play a key role in how elements are used in industry and technology, influencing their applications and how they are combined to form compounds.

Chemical Reactions

Chemical reactions involve the transformation of substances through the breaking and forming of chemical bonds. They result in the creation of one or more new products. This process is fundamental to chemistry and is characterized by the rearrangement of atoms.

• Indicators of a chemical reaction can include color change, temperature change, gas production, and the formation of a precipitate.
• A classic example is the reaction between sodium and chlorine to form table salt, where new chemical bonds are formed, creating a stable compound.

Understanding chemical reactions is essential for predicting product outcomes and controlling reaction conditions in various applications. From energy production to manufacturing, the principles of chemical reactions are applied across numerous fields, demonstrating their pivotal role in both natural phenomena and industrial processes.