Question

Describe each of the following as a physical or chemical property: a. Neon is a colorless gas at room temperature. b. Apple slices turn brown when they are exposed to air. c. Phosphorus will ignite when exposed to air. d. At room temperature, mercury is a liquid. e. Propane gas is compressed to a liquid for placement \(\mathrm{in} \mathrm{a}\) small cylinder.

Short answer

a. Physical, b. Chemical, c. Chemical, d. Physical, e. Physical.

Step-by-step solution

- Identifying the Nature of a Property

Determine if a property is physical or chemical by checking if it changes the substance's identity. Physical properties describe the state or appearance without changing the composition. Chemical properties describe the substance's ability to change into a new substance.

- Analyzing Part (a)

Neon is a colorless gas at room temperature. Since this describes the state and appearance of neon without altering its composition, it is a physical property.

- Analyzing Part (b)

Apple slices turn brown when they are exposed to air. This is a result of a chemical reaction (oxidation), which changes the composition of the apple slice. Therefore, this is a chemical property.

- Analyzing Part (c)

Phosphorus will ignite when exposed to air. Ignition leads to combustion, a chemical reaction that produces new substances. Thus, this is a chemical property.

- Analyzing Part (d)

At room temperature, mercury is a liquid. This statement describes the state of mercury without changing its composition, making it a physical property.

- Analyzing Part (e)

Propane gas is compressed to a liquid for placement in a small cylinder. Compressing propane changes its state but not its chemical identity. Hence, this is a physical property.

Key concepts

physical properties

Physical properties are characteristics of a substance that can be observed or measured without changing its chemical composition. These properties describe the state or appearance of the substance. Examples include:

• Color
• Density
• Volume
• State of Matter (solid, liquid, gas)

For example, in the exercise where it's noted that 'Neon is a colorless gas at room temperature' and 'At room temperature, mercury is a liquid', these properties refer to the state and appearance of neon and mercury without altering their compositions. Thus, these statements are describing their physical properties.

chemical properties

Chemical properties define how a substance interacts with other substances, leading to a change in its chemical composition. These properties are crucial in predicting the behavior of a substance in chemical reactions. Typical chemical properties include:

• Reactivity with oxygen (oxidation)
• Flammability
• Acidity or basicity
• Ability to rust

In our exercise, when 'Apple slices turn brown when they are exposed to air' and 'Phosphorus will ignite when exposed to air' are mentioned, they signify chemical properties. The apple slices turning brown is a chemical reaction (oxidation), and phosphorus igniting also involves a chemical change. Both illustrate how the substances change their composition when they react with air.

substance identity

Substance identity refers to the defining characteristics of a substance that determine its chemical composition and structure. If these characteristics change, the substance itself changes and transforms into a different substance. Identifying substance identity is critical in distinguishing between physical and chemical properties.
For instance, compressing propane gas into a liquid form changes its state but does not alter its chemical composition. Hence, the identity remains the same, which signals that it is a physical property. However, when phosphorus ignites in the presence of air, it transforms into a different substance, indicating a change in substance identity due to a chemical reaction.

state of matter

The state of matter describes the physical form a substance takes: solid, liquid, or gas. The state of matter is a prominent physical property as it involves changes in appearance without altering the substance's chemical identity. Temperature and pressure often influence the state of matter.
For example, neon being a colorless gas at room temperature and mercury being a liquid at room temperature are observations about their states of matter. Similarly, the physical transformation of propane gas to a liquid state under compression changes its physical form, demonstrating changes in the state of matter.

oxidation

Oxidation is a specific type of chemical reaction where a substance reacts with oxygen, often resulting in a change in the substance's chemical composition. Common examples of oxidation include rusting of iron, tarnishing of silver, and the browning of apple slices when exposed to air.
When apple slices turn brown in the exercise, this happens due to oxidation. Similarly, phosphorus igniting in air is another case of oxidation, where the element reacts with oxygen, leading to the formation of a new substance. These examples highlight oxidation as a critical chemical property that alters the substance's identity.