Problem 26 - Chemistry The Molecular Nature of Matter

Question

Explain the difference between the names of \(\mathrm{H}_{2} \mathrm{Se}(g)\) and \(\mathrm{H}_{2} \mathrm{Se}(a q)\)

Step-by-Step Solution

Answer

\(\mathrm{H}_{2} \mathrm{Se}(g)\) is called hydrogen selenide gas, and \(\mathrm{H}_{2} \mathrm{Se}(aq)\) is called aqueous hydrogen selenide.

Step 1: Understanding the Chemical Formulas

Identify that both \(\mathrm{H}_{2} \mathrm{Se}\) represent the chemical compound hydrogen selenide, which is composed of two hydrogen atoms and one selenium atom.

Step 2: Recognizing the Physical State Symbols

Acknowledge that \(g\) and \(aq\) after the formulas denote the physical states of the compound: \(g\) stands for gas, and \(aq\) indicates the compound is in aqueous solution, meaning dissolved in water.

Step 3: Understanding the Context

Understand that the naming convention reflects the physical state: \(\mathrm{H}_{2} \mathrm{Se}(g)\) is called hydrogen selenide gas; while \(\mathrm{H}_{2} \mathrm{Se}(aq)\) would be referred to as aqueous hydrogen selenide.

Key Concepts

Hydrogen Selenide

Hydrogen selenide, also known by its chemical formula (H_{2}Se), is a compound consisting of hydrogen and selenium. It's a hydride of selenium, and in its pure form at room temperature, it is a toxic and colorless gas with a rotting egg smell. Hydrogen selenide has notable uses in the semiconductor industry but requires careful handling due to its toxicity and flammability.

Under different conditions, hydrogen selenide can change in its physical state, exhibiting properties unique to its state of matter. For instance, when dissolved in water, it forms selenious acid. Students often encounter hydrogen selenide in problems related to chemical reactions and stoichiometry, where understanding its properties and reactions is crucial.

Chemical Formulas

Chemical formulas, like (H_{2}Se), serve as shorthand notations that provide a wealth of information about a substance. They indicate both the types and numbers of atoms that make up a chemical compound. For instance, the formula for hydrogen selenide tells us there are two hydrogen atoms ((H)) and one selenium atom ((Se)) in each molecule of the compound.

Deciphering Chemical Formulas

Understanding how to interpret these formulas is a foundational skill in chemistry. Students typically learn to identify molecular and empirical formulas, calculate molar masses, and use formulas in balancing chemical equations. It's important to emphasize that while chemical formulas reflect the composition, they do not indicate how atoms are bonded or configured in three-dimensional space.

Physical States of Matter

The physical states of matter refer to distinct forms that different phases of matter take on. The most familiar are solid, liquid, gas, and plasma. In the context of chemical nomenclature, the state of matter is often indicated alongside the chemical formula to convey the substance's physical form under given conditions.

For example, (H_{2}Se(g)) specifies that hydrogen selenide is in its gaseous state. In contrast, (H_{2}Se(aq)) signals that hydrogen selenide is dissolved in water, indicating an aqueous solution. This distinction is key as the properties and reactivity of a substance can greatly differ depending on its state of matter. Students should be familiar not just with the symbols themselves but also with how changes in temperature and pressure can affect a substance's state.