Formation Equations: Videos & Practice Problems

Elements on the periodic table are found in different standard states at room temperature (approximately 25 degrees Celsius) and standard pressure (approximately one atmosphere), which include solids, liquids, and gases. Noble gases like helium and radon are monoatomic gases, while hydrogen ($H_2$), nitrogen ($N_2$), oxygen ($O_2$), fluorine ($F_2$), and chlorine (${\mathrm{Cl}}_2$) exist as diatomic gases. Bromine (${\mathrm{Br}}_2$) and mercury ($\mathrm{Hg}$) are the only liquid elements at room temperature, with bromine being diatomic and mercury monoatomic. Most other elements are solid and monoatomic in their natural state. Phosphorus ($P_4$), sulfur ($S_8$), selenium (${\mathrm{Se}}_8$), and tellurium (${\mathrm{Te}}_8$) exist as polyatomic molecules, while iodine ($I_2$) is diatomic. Elements with high atomic masses or those synthesized in laboratories may not have a defined phase under standard conditions. The molecular arrangement varies across phases: tightly packed in solids, more freedom of movement in liquids, and widely spread in gases. Understanding these states is essential for comprehending the physical properties and behavior of elements under different conditions.

Formation Equations

Elements of the periodic table can exist in different standard states, which refer to their natural forms at room temperature (approximately 25 degrees Celsius) and standard pressure (about 1 atmosphere). These states can be categorized as solids, liquids, or gases.

In the gaseous state, certain elements are represented in red on the periodic table. Noble gases, such as helium (He) through radon (Rn), exist as monoatomic gases. Other gases, like hydrogen (H₂), nitrogen (N₂), oxygen (O₂), fluorine (F₂), and chlorine (Cl₂), are diatomic, meaning they consist of two atoms bonded together.

Liquid elements include bromine (Br₂), which is diatomic, and mercury (Hg), which is monoatomic. The majority of elements in their natural state are solids, typically existing as monoatomic structures. However, some elements, particularly those with high atomic masses, are unstable and do not have a defined phase at standard conditions; these are often synthesized in laboratories.

Understanding the molecular arrangement in different states is crucial. In solids, molecules are tightly packed, while in liquids, they can move more freely around one another. In gases, molecules are widely spaced apart.

Additionally, some elements do not exist as monoatomic or diatomic forms. For instance, phosphorus (P) exists as P₄, sulfur (S) as S₈, and selenium (Se) and tellurium (Te) as Se₈ and Te₈, respectively. Iodine (I) is also diatomic, existing as I₂. Recognizing these various forms of elements in their standard or natural states is essential for understanding their behavior and properties in different conditions.

Formation Equations Example 1

In chemistry, the standard state of an element refers to its physical state at a specified temperature and pressure, typically 25°C and 1 atmosphere. Understanding the standard states of elements is crucial for predicting their behavior in reactions and their physical properties.

For example, iodine (I₂) exists as a solid in its standard state, while oxygen (O₂) is a diatomic gas. It's important to note that ozone (O₃) is a different allotrope of oxygen and does not represent the standard state of oxygen. Neon (Ne), a noble gas, is monoatomic and exists as a gas in its standard state. Boron (B), on the other hand, is a solid in its standard state and does not exist as B₂ gas.

Thus, among the options provided, the only element that is found in its standard state is neon gas (Ne), as it is a noble gas and exists in a monoatomic gaseous form under standard conditions.

Formation Equations Example 2

In a formation equation, the standard states of elements combine to form one mole of a product. For Methanethiol, represented as CH₃SH, the process begins by writing the compound as the product with a coefficient of 1, indicating the formation of one mole.

Next, identify the standard states of the elements that constitute Methanethiol. The elements involved are carbon, hydrogen, and sulfur. Carbon is monoatomic and typically exists in its most stable form as graphite (C), hydrogen is diatomic (H₂) and is a gas, while sulfur is polyatomic, commonly found as S₈ in solid form.

The formation equation can be constructed as follows:

1 C (graphite) + 2 H₂ + (1/8) S₈ → 1 CH₃SH

To balance the equation, we analyze the number of atoms on both sides. On the product side, we have 1 carbon, 4 hydrogens, and 1 sulfur. On the reactant side, we start with 1 carbon and 2 hydrogens, requiring adjustments. Since we cannot change the coefficient of the product, we introduce a coefficient of 2 for hydrogen, which gives us 4 hydrogens. For sulfur, we need to account for the 1 sulfur atom in the product, which requires a coefficient of 1/8 for S₈ to balance the equation.

Thus, the balanced formation equation for Methanethiol is:

1 C (graphite) + 2 H₂ + (1/8) S₈ → 1 CH₃SH

This equation illustrates the combination of elements in their standard states to yield one mole of Methanethiol, highlighting the unique aspect of formation equations where fractional coefficients can be utilized.

Which of the following represents the formation equation for barium nitrate, Ba(NO₃)₂?

• A. Ba²⁺ (aq) + 2 NO₃^– (aq) → Ba(NO₃)₂ (aq)
• B. Ba(NO₃)₂ (aq) → Ba (s) + N₂ (g) + 3 O₂ (g)
• C. Ba (s) + N₂ (g) + 3 O₂ (g) → Ba(NO₃)₂ (aq)
• D. Ba (s) + 2 N (g) + 6 O (g) → Ba(NO₃)₂ (aq)

Answer: (C)

Identify a substance that is not in its standard state.

• A. Cl₂
• B. Li
• C. H
• D. P₄
• E. Ar

Answer: (C)

Ibuprofen is used as an anti-inflammatory agent used to deal with pain and bring down fevers. If it has a molecular formula of C₁₃H­₁₈O₂, determine the balanced chemical equation that would give you directly the enthalpy of formation for ibuprofen. 

• A. 13 C (graphite) + H₂ (g) + O₂ (g) → C₁₃H­₁₈O₂ (s)
• B. 13 C (graphite) + 9 H₂ (g) + 2 O₂ (g) → C₁₃H­₁₈O₂ (s)
• C. 13 C (graphite) + 8 H₂ (g) + O₂ (g) → C₁₃H­₁₈O₂ (s)
• D. 13 C (graphite) + 9 H₂ (g) + O₂ (g) → C₁₃H­₁₈O₂ (s)

Answer: (D)

Here’s what students ask on this topic:

What are the standard states of elements at room temperature and pressure?

At room temperature (approximately 25 degrees Celsius) and standard pressure (approximately one atmosphere), elements exist in different standard states. Noble gases like helium and radon are monoatomic gases. Hydrogen (H₂), nitrogen (N₂), oxygen (O₂), fluorine (F₂), and chlorine (Cl₂) are diatomic gases. Bromine (Br₂) and mercury (Hg) are the only liquid elements, with bromine being diatomic and mercury monoatomic. Most other elements are solid and monoatomic in their natural state. Phosphorus (P₄), sulfur (S₈), selenium (Se₈), and tellurium (Te₈) exist as polyatomic molecules, while iodine (I₂) is diatomic. Elements with high atomic masses or those synthesized in laboratories may not have a defined phase under standard conditions.

Why do some elements exist as diatomic molecules in their natural state?

Some elements exist as diatomic molecules in their natural state because it is energetically favorable for them to pair up and share electrons, achieving a more stable electronic configuration. For example, hydrogen (H₂), nitrogen (N₂), oxygen (O₂), fluorine (F₂), chlorine (Cl₂), bromine (Br₂), and iodine (I₂) form diatomic molecules. This pairing allows them to complete their valence electron shells, resulting in a lower energy state and increased stability compared to existing as individual atoms.

What is the difference between monoatomic and polyatomic elements?

Monoatomic elements consist of single atoms that are not bonded to other atoms. Examples include noble gases like helium (He) and mercury (Hg) in their natural states. Polyatomic elements, on the other hand, consist of molecules formed by multiple atoms bonded together. Examples include phosphorus (P₄), sulfur (S₈), selenium (Se₈), and tellurium (Te₈). These elements form stable structures by sharing electrons among multiple atoms, resulting in molecules with more complex arrangements compared to monoatomic elements.

How do the physical properties of elements vary across different phases?

The physical properties of elements vary significantly across different phases. In the solid phase, molecules are tightly packed together, resulting in a definite shape and volume. Solids are generally rigid and have high density. In the liquid phase, molecules have more freedom to move around one another, allowing liquids to flow and take the shape of their container while maintaining a constant volume. Liquids have moderate density. In the gas phase, molecules are widely spread apart, leading to no definite shape or volume. Gases can expand to fill any container and have low density. These variations in molecular arrangement and movement account for the distinct physical properties observed in each phase.

Why do some elements not have a defined phase under standard conditions?

Some elements do not have a defined phase under standard conditions because they are either highly unstable or have been synthesized in laboratories. Elements with high atomic masses, such as those at the bottom of the periodic table, often exhibit instability due to the large number of protons and neutrons in their nuclei. This instability can lead to rapid decay or transformation into other elements. Additionally, synthetic elements created in laboratories may not exist naturally and can have very short half-lives, preventing them from having a stable phase at room temperature and standard pressure.