Problem 30 - Chemistry: Atoms First

Question

A 2.0-liter volume of hydrogen gas combined with 1.0 liter of oxygen gas to produce 2.0 liters of water vapor. Does oxygen undergo a chemical or physical change?

Step-by-Step Solution

Answer

Oxygen undergoes a chemical change because its chemical identity is altered when it reacts with hydrogen to form water vapor.

Step 1: Identify the Type of Change

To determine whether oxygen undergoes a chemical or physical change, identify if the substance's chemical identity changes during the process.

Step 2: Analyze the Reaction

In the reaction, hydrogen gas (H2) and oxygen gas (O2) react to form water vapor (H2O). The substances on the reactants side are different from the product, indicating that a chemical reaction has occurred.

Step 3: Determine the Change for Oxygen

Oxygen gas (O2) is a diatomic molecule consisting of two oxygen atoms bonded together. In water vapor (H2O), oxygen is now bonded to hydrogen. The chemical structure and properties of oxygen have changed, confirming a chemical change.

Key Concepts

Chemical Reactions

A chemical reaction is a process by which substances interact to form new compounds with different properties. The very essence of a chemical reaction is the rearrangement of atoms and changing of chemical bonds. Take, for example, the synthesis of water vapor from hydrogen and oxygen gases. When these two elements combine, they undergo a chemical reaction. Hydrogen (H_2) and Oxygen (O_2) are diatomic molecules, meaning that each molecule is composed of two atoms. During the reaction, these atoms rearrange to form water (H_2O), a stable compound composed of two hydrogen atoms bonding to one oxygen atom.

This process represents a transformation at a molecular level, resulting in a substance that exhibits properties distinct from those of the original reactants. It is important to notice that these reactions are subject to the law of conservation of mass, which states that the mass of the reactants equals the mass of the products. In our example, the total volume of gases before the reaction (3.0 liters) is equal to the volume of water vapor produced (2.0 liters), adhering to this law.

Understanding the molecular interactions involved in chemical reactions allows us to predict the properties of the resulting substances, which is a core concept in chemistry and critical to various scientific and industrial processes.

Chemical Identity

Chemical identity refers to the unique characteristics of a substance that are defined by its molecular composition and structure. Each chemical compound has a distinct identity because of the arrangement of its atoms and the types of bonds between them. In the context of our example, oxygen gas initially has the chemical identity of O_2, featuring a double bond linking two oxygen atoms. When it reacts with hydrogen to form water, its chemical identity is altered as it becomes part of a new compound, H_2O, with distinct arrangements and bonds.

The alteration in the chemical identity during a reaction is a hallmark of a chemical change. Unlike a physical change, which involves a transformation in the form or state of matter without a change in the chemical composition, a chemical change results in the formation of entirely new substances. These changes are not reversible by simple physical means because the original materials no longer exist as they were, fundamentally differentiating chemical changes from physical changes.

When approaching a problem in chemistry, it is crucial to discern the type of change occurring to ensure a correct understanding of the concepts involved. Chemical identity plays a key role in defining the nature of the reactants and products in a reaction.

Properties of Oxygen

Oxygen is a fundamental element that exists naturally as a diatomic molecule, denoted as O_2. It is essential for life processes such as respiration, and it plays a significant role in combustion and oxidation reactions. Being the most abundant element by mass in the Earth's crust, its properties are of great importance to many scientific fields.

Oxygen in its diatomic form is a gas under standard conditions with unique properties that distinguish it from other elements. Some of the key properties include its ability to support combustion, its colorless and odorless nature, and its paramagnetic characteristic due to unpaired electrons in its molecular orbital. These properties are a direct result of oxygen's electronic configuration and molecular structure.

In the context of chemical reactions, the properties of oxygen determine how it interacts with other elements and compounds. For instance, in the formation of water vapor through the reaction with hydrogen, the reactivity of oxygen is a vital factor that allows the formation of the water molecule. The understanding of how oxygen's properties influence its behavior in reactions is crucial for comprehensively grasping the principles of chemistry. Additionally, when involved in chemical changes, the properties of oxygen adjust to accommodate the new chemical environments, as seen in its conversion from O_2 to a part of H_2O in water.