Problem 92 - Chemistry Matter and Change

Question

Indicate whether combining the following elements yields a compound or a mixture, \begin{equation} \begin{array}{l}{\text { a. } \mathrm{H}_{2}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow \text { water }} \\ {\text { b. } \mathrm{N}_{2}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow \text { air }}\end{array} \end{equation}

Step-by-Step Solution

Answer

(a) forms a compound; (b) forms a mixture.

Step 1: Understanding the Definitions

A compound is a substance formed when two or more chemical elements are chemically bonded together. A mixture consists of two or more different substances, which are not chemically bonded.

Step 2: Analyzing Reaction (a)

In reaction (a), hydrogen gas (H_2(g)) reacts with oxygen gas (O_2(g)) to produce water. The resulting substance is water, in which hydrogen and oxygen atoms are chemically bonded to form a new substance. This is an example of a compound.

Step 3: Analyzing Reaction (b)

In reaction (b), nitrogen gas (N_2(g)) and oxygen gas (O_2(g)) are mixed to form air. Nitrogen and oxygen do not chemically bond in this process; they exist as separate components within the air. Thus, this is an example of a mixture.

Key Concepts

Compounds

Compounds are materials made from two or more different elements that are chemically bonded together. In the context of reaction (a) from our exercise, hydrogen ( H_2(g) ) and oxygen ( O_2(g) ) gases combine to form water. This results in a chemical bond where the elements share or exchange electrons and form a stable molecule ( H_2O ) . This newly formed substance has properties distinct from those of the individual elements that make it up. For instance, water has unique characteristics quite different from gaseous hydrogen or oxygen.

• Compounds are consistent and always have the same composition.
• They can only be separated into their pure elements by chemical reactions.
• Properties of a compound differ significantly from its component elements.

This is a hallmark of compounds—an entirely new entity with its own identity exploiting chemical bonding principles to link atoms firmly.

Mixtures

In pure mixtures, elements or molecules are combined without undergoing any chemical bonding. Consequently, the individual substances maintain their properties even when mixed. Examining reaction (b), nitrogen ( N_2(g) ) and oxygen ( O_2(g) ) mix to form air, but they are not chemically changed or bonded in this process. This type of combination results in a physical mixture where the individual gas molecules avoid any new interactions.

• Mixtures possess variable composition, meaning the proportions of constituent elements can vary.
• They can be separated into their components by physical means such as filtration or evaporation.
• The properties of a mixture are usually just an average of the properties of its components.

For mixtures, interactions between substances are simply physical, keeping each substance's attributes intact. This makes mixtures versatile yet distinct from the formation of chemical compounds.

Chemical Bonding

Chemical bonding is the force that allows elements to come together and form compounds. It is the compelling interaction between atoms that involve the transfer or sharing of electrons to create stable substances. When hydrogen and oxygen form water, chemical bonding is what holds the elements tightly together forming ( H_2O ) . Here are the key types of chemical bonds:

• Covalent Bonds: Atoms share pairs of electrons.
• Ionic Bonds: Electrons are transferred from one atom to another, creating charged ions.
• Metallic Bonds: Electrons are shared over many nuclei forming a "sea of electrons" characteristic of metals.

Chemical bonding alters the properties of the original atoms, leading to substances with unique physical and chemical characteristics. This manipulation of electrons is fundamental to the creation of diverse materials we encounter in chemistry.

Element Reactions

Element reactions refer to the processes where elements interact, resulting in either physical mixtures or chemically bonded compounds. Reaction (a) where hydrogen and oxygen form water involves a chemical reaction leading to a stable compound. In contrast, reaction (b) demonstrates a physical mixing, not producing new molecular structures, thus classified as a mixture.

• Reactions that lead to compounds involve breaking and forming of new bonds between atoms.
• Physical mixing does not change the chemical identity of the substances involved.

Element reactions span a spectrum from mere physical combinations to complex chemical transformations. The type and result of the reaction depend heavily on whether new chemical bonds are established, creating compounds, or if elements are merely intermixed, forming a mixture. Grasping these differences is crucial in understanding chemical principles and the diversity of material formations.