Problem 92 - Chemistry Matter and Change

Question

Indicate whether combining the following elements yields a compound or a mixture, a. \(H_{2}(g)+O_{2}(g) \rightarrow \mathrm{water}\) b. \(N_{2}(g)+O_{2}(g) \rightarrow \mathrm{air}\)

Step-by-Step Solution

Answer

Reaction a: Combining hydrogen gas (\(H_{2}\)) and oxygen gas (\(O_{2}\)) forms water, a compound. Reaction b: Combining nitrogen gas (\(N_{2}\)) and oxygen gas (\(O_{2}\)) forms air, a mixture.

Step 1: Reaction a: \(H_{2}(g)+O_{2}(g) \rightarrow \mathrm{water}\)

When hydrogen gas (\(H_{2}\)) reacts with oxygen gas (\(O_{2}\)), they form water. The reaction can be represented with the balanced chemical equation: \(2H_{2}(g) + O_{2}(g) \rightarrow 2H_2O(l)\). In the reaction, hydrogen and oxygen are chemically combined to form water, which is a new substance with different properties from the reactants. Therefore, reaction a results in a compound.

Step 2: Reaction b: \(N_{2}(g)+O_{2}(g) \rightarrow \mathrm{air}\)

When nitrogen gas (\(N_{2}\)) is combined with oxygen gas (\(O_{2}\)), they form air. Air is a mixture of several gases, namely, nitrogen and oxygen, and other trace gases. The nitrogen and oxygen in the air are not chemically combined but exist together in the form of a mixture. Therefore, reaction b results in a mixture. In conclusion, reaction a results in a compound while reaction b results in a mixture.

Key Concepts

Compounds

In chemistry, a compound is a substance that forms when two or more elements are chemically bonded together. This bonding creates a distinct substance with properties that differ from the original elements. For instance, in the combination where hydrogen gas ( H_{2}(g) ) reacts with oxygen gas ( O_{2}(g) ) to form water, a new compound is produced. This process involves a chemical reaction where the elements share or transfer electrons to form a stable entity, known as a compound.
One key feature of compounds is that they have a fixed ratio of atoms. This means that the elements always combine in the same proportions, ensuring consistency in the compound's properties. For example, water always has two hydrogen atoms for every one oxygen atom, represented as H_2O .

• Compounds have uniform properties and composition.
• They can be broken down into simpler substances through chemical reactions.
• The elements in a compound cannot be separated by physical means.

Mixtures

Contrary to compounds, mixtures are combinations of two or more substances where each retains its individual chemical properties. They do not involve chemical bonding between the components, which means each substance in a mixture remains unchanged chemically.
The air we breathe is a classic example of a mixture. It consists primarily of nitrogen ( N_2(g) ) and oxygen ( O_2(g) ), along with small amounts of other gases. These gases are mixed together but not chemically bonded, allowing each to maintain its distinct properties.
The composition of mixtures can vary. This variability means that mixtures can be heterogenous, like a salad (where components are visibly distinct), or homogenous, like solutions (where components are uniformly distributed).
Some key characteristics of mixtures include:

• Their components can be separated by physical methods like filtration or distillation.
• They do not have a definite composition or formula.
• They maintain the original properties of their components.

Chemical Equations

Chemical equations are symbolic representations of chemical reactions, showing the reactants and products involved. They provide a concise way to convey all the necessary information about the chemical changes taking place.
When hydrogen and oxygen gases react, the equation 2H_2(g) + O_2(g) ightarrow 2H_2O(l) represents the formation of water. This equation does more than tell us that water is formed; it also indicates the proportion of the reactants and products.
Chemical equations must be balanced to reflect the law of conservation of mass. This law states that matter cannot be created or destroyed in a chemical reaction. Thus, the number of atoms for each element must be the same on both sides of an equation.

• Coefficients in a chemical equation show the ratio of moles of each substance involved.
• Subscripts, found in chemical formulas, indicate the number of atoms in each molecule.
• Symbols like (g) for gas and (l) for liquid indicate the state of the substances.

Reaction Types

Chemical reactions can be classified into various types based on how reactants interact and change into products. Understanding different reaction types helps predict the outcomes and products of chemical processes.
The reaction between hydrogen and oxygen is an example of a synthesis reaction, where two or more simple substances combine to form a more complex product. This is a fundamental type of reaction that often results in the formation of compounds.
Conversely, the formation of air from nitrogen and oxygen involves a physical combination without forming a new substance, hence it is categorically a physical process rather than a chemical reaction. However, certain chemical reactions such as combustion can occur within the mixture of gases present in the air.
Here are a few common reaction types:

• Synthesis reactions: Two or more substances combine to form a single compound.
• Decomposition reactions: Compounds break down into simpler substances.
• Combustion reactions: A substance reacts with oxygen, often producing heat and light.

Each reaction type is unique and governed by specific principles that dictate the formation and breaking of bonds in chemical processes.