Problem 17 - Chemistry and Chemical Reactivity

Question

Which part of the description of a compound or element refers to its physical properties and which to its chemical properties? (a) The colorless liquid ethanol burns in air. (b) The shiny metal aluminum reacts readily with orange-red bromine.

Step-by-Step Solution

Answer

Ethanol's physical property is being a colorless liquid; its chemical property is burning. Aluminum's physical property is being shiny; its chemical property is reacting with bromine.

Step 1: Identify Physical Properties in Part (a)

Physical properties are characteristics of matter that can be observed or measured without changing its composition. In part (a), the phrase "colorless liquid ethanol" describes its physical property because it refers to its appearance and state of matter.

Step 2: Identify Chemical Properties in Part (a)

Chemical properties describe the behavior of a substance when it undergoes a chemical change. In part (a), the phrase "burns in air" is a chemical property of ethanol, as it refers to a reaction (combustion) with oxygen in the air.

Step 3: Identify Physical Properties in Part (b)

In part (b), the description "shiny metal aluminum" indicates a physical property. The shininess and metallic nature refer to the appearance and physical state of aluminum, which can be observed without changing its composition.

Step 4: Identify Chemical Properties in Part (b)

In part (b), the phrase "reacts readily with orange-red bromine" reflects a chemical property. It describes a chemical reaction between aluminum and bromine, indicating how aluminum behaves chemically.

Key Concepts

Physical Properties

Physical properties are the characteristics of a substance you can observe or measure without altering its identity. They describe the matter's traits like color, state, texture, and density, all of which can be observed physically. For example, when we say ethanol is a "colorless liquid," we are noting its physical properties.

Such properties are essential in identifying substances and predicting how they interact with other materials. They include properties like:

• Color
• Odor
• State of matter (solid, liquid, gas)
• Melting and boiling points
• Density
• Texture and shininess (for metals)

Understanding these properties helps in tasks such as separating mixtures or determining purity without causing any changes to the original substance.

Chemical Reactions

A chemical reaction occurs when substances interact to form new substances with different properties. It involves changes at a molecular level, where bonds between atoms are broken and new ones are formed.

An example of a chemical reaction is combustion, where ethanol "burns in air." This process involves ethanol reacting with oxygen to produce carbon dioxide, water, and energy (heat and light). Chemical reactions are often identified by:

• Color change
• Formation of a precipitate
• Gas production
• Temperature change
• Light production

Recognizing these changes can help in understanding processes like respiration, rusting, and cooking, and why these reactions are often irreversible without another chemical change.

Chemical Properties

Chemical properties describe a substance's potential to undergo a chemical change, revealing how it reacts with other substances. It indicates what happens when it engages in a chemical reaction.

For instance, when aluminum "reacts readily with orange-red bromine," we are discussing its chemical property. This shows aluminum's tendency and ability to form new compounds with bromine.

These properties are vital in predicting chemical interactions and include:

• Reactivity with other chemicals
• Flammability
• Acidity or basicity
• Oxidation states
• Corrosion resistance

Chemical properties are crucial in fields like chemistry and materials engineering, guiding how substances are stored, handled, and utilized.

Matter Observations

Observing matter involves examining both physical and chemical properties to understand its nature and behavior. These observations can be simple, such as noting a substance's color, or complex, involving reactions under various conditions.

By observing substances like ethanol and aluminum, we recognize their physical forms and chemical behaviors. Observations help us predict outcomes in reactions and understand why certain substances are used over others in particular applications or industrial processes.

Effective observation analyzes both changes that don't involve altering chemical identities and those that do. It enables scientists and students to learn more about the world around them, from everyday phenoms to intricate molecular interactions.