Problem 99 - General Chemistry

Question

Describe each of the following as a physical or chemical property of each listed chemical substance. A baking soda reacts with vinegar B ice melts at \(0^{\circ} \mathrm{C}\) C graphite is a soft, black solid D hydrogen burns in air

Step-by-Step Solution

Answer

A and D are chemical properties; B and C are physical properties.

Step 1: Identify Reactivity

Determine if the statement about baking soda reacting with vinegar describes how the substance changes composition. Reacting with another substance to form a new product is a chemical property. Hence, baking soda's reaction with vinegar is a chemical property.

Step 2: Phase Change Observation

Identify if melting involves a change in the chemical composition of ice. Melting is a change of state from solid to liquid, which does not alter the chemical identity of the substance. Therefore, the melting point of ice is a physical property.

Step 3: Physical Characteristics Assessment

Examine if the description of graphite relates to its composition. The description of graphite as a soft, black solid indicates its physical appearance and texture, without any mention of a chemical change. Thus, the property is physical.

Step 4: Flammability Check

Determine if hydrogen burning in air reflects a change in chemical composition. Burning usually indicates a reaction with oxygen (combustion), resulting in a new substance, which is a chemical change. Hence, hydrogen burning in air is a chemical property.

Key Concepts

Chemical Properties

Chemical properties describe the potential of a substance to undergo a chemical change or reaction due to its composition. This involves how a substance can transform into one or more different substances. A great way to identify a chemical property is to observe the substance's interactions with other substances, such as its reactivity. For instance, when baking soda reacts with vinegar, it undergoes a noticeable change. This reaction results in the formation of new compounds, proving that this is a chemical property. Similarly, when hydrogen burns in air, it combines with oxygen to form water. This formation of a new chemical from the reaction implies it's a chemical property, emphasized by the production of heat and light.

Physical Properties

Physical properties are characteristics of matter that can be observed or measured without changing the substance's composition. These properties include attributes like color, density, hardness, and melting and boiling points.An example of a physical property is the description of graphite as a soft, black solid. This observation only relates to its appearance and does not involve any chemical transformation or reaction. This is why these descriptors are classified as physical properties. Another example is ice melting at \(0^{\circ} \mathrm{C} \). Melting is a phase transition where the ice turns into water, but its chemical structure remains H₂O throughout, hence a physical property.

Reactivity

Reactivity refers to how readily a chemical substance undergoes a chemical reaction with other substances. The reactions can vary greatly depending on the nature of the reactants and the conditions under which the reaction takes place. A critical aspect of reactivity is the formation of new substances. For example, the reaction of baking soda with vinegar is a demonstration of its reactivity. Such a chemical reaction might produce gas bubbles (carbon dioxide in this case), hinting at a change in the chemical structure of the original substances. Hydrogen's ability to react with oxygen in combustion also showcases high reactivity, where new water molecules are formed.

Phase Change

Phase changes involve the transformation of matter from one state to another, such as solid to liquid, liquid to gas, or solid to gas. These changes are usually physical changes because they do not alter the chemical structure of the substance. For example, when ice melts, it transitions from a solid to a liquid state. During this process, the molecules in ice (H₂O) simply gain energy and move more freely to form liquid water, maintaining their molecular structure. Thus, phase changes are identified as physical properties because the identity of the substance remains the same throughout the process.