Question

Elements are formed by nuclear fusion reactions. One step in this process is so-called "helium burning", the fusion of two helium- 4 nuclei to produce beryllium- 8 . Write a balanced nuclear equation to represent this process.

Short answer

\(^4_2\text{He} + ^4_2\text{He} \rightarrow ^8_4\text{Be}\).

Step-by-step solution

Identify Reactants

In the helium burning process, the reactants are two helium-4 nuclei. Helium-4 is represented by the chemical symbol \(^4_2\text{He}\). The subscript 2 indicates the atomic number (number of protons) and the superscript 4 indicates the mass number (total number of protons and neutrons).

Identify the Product

The product of the fusion of two helium-4 nuclei is beryllium-8. Beryllium-8 is represented by the chemical symbol \(^8_4\text{Be}\). Similarly, the subscript 4 is the atomic number and the superscript 8 is the mass number.

Write the Nuclear Equation

To write the nuclear equation, place the reactants and product on opposite sides of the equation as follows: \(^4_2\text{He} + ^4_2\text{He} \rightarrow ^8_4\text{Be}\).

Verify the Equation

Check that the atomic numbers and mass numbers are balanced on both sides of the equation. The total atomic number on the left is 2 + 2 = 4, and on the right, it is also 4. The total mass number on the left is 4 + 4 = 8, and on the right, it is also 8. The equation is balanced.

Key concepts

Helium Burning

Helium burning is a fascinating and essential process in the lifecycle of stars. It's a type of nuclear fusion reaction that occurs in the cores of stars where helium nuclei are transformed into heavier elements. Specifically, the process involves the fusion of two helium-4 nuclei to form a beryllium-8 nucleus. This reaction takes place at extremely high temperatures and pressures.
Helium burning is critical because it sets the stage for the creation of even heavier elements in stars. Once beryllium-8 is formed, it can further interact with more helium nuclei to form carbon. This ongoing fusion process is what enables stars to emit energy and light, a fundamental mechanism that keeps stars shining for millions or even billions of years.

Balanced Nuclear Equation

The balanced nuclear equation is an essential element in representing nuclear reactions. In the context of helium burning, balancing the equation means ensuring that the number of protons and neutrons on the reactant side matches those on the product side.

• Reactants: Two helium-4 nuclei with the formula \(^4_2\text{He}\)
• Product: One beryllium-8 nucleus expressed as \(^8_4\text{Be}\)

To balance this nuclear equation, sum up the atomic and mass numbers on each side. For helium burning, the total atomic number is 2 + 2 = 4, and the total mass number is 4 + 4 = 8 on the reactant side, which equals the atomic and mass number of beryllium-8 on the product side.
This balance confirms the conservation of mass and atomic number, which are crucial principles in nuclear chemistry.

Helium-4

Helium-4, often denoted as \(^4_2\text{He}\), is one of the most common isotopes of helium, making up about 99% of all helium found in nature. It consists of two protons and two neutrons in its nucleus, giving it the mass number of 4 and atomic number of 2.
Helium-4 is formed through the process of nuclear fusion in the cores of stars. It results from the fusion of hydrogen nuclei, which is an integral part of stellar nucleosynthesis. Helium-4 is also significant because it serves as the starting material for helium burning, which transforms it into heavier elements like beryllium-8 during the lifecycle of a star.

Beryllium-8

Beryllium-8, represented as \(^8_4\text{Be}\), is a fascinating and somewhat unstable isotope of beryllium. It has a total of 4 protons and 4 neutrons, lending it a mass number of 8 and atomic number of 4.
In the context of helium burning, beryllium-8 is a transient product of the fusion of two helium-4 nuclei. While beryllium-8 itself is not stable and quickly decays back into two helium nuclei, it plays a critical role in the cosmic production of heavier elements, especially in high-pressure environments found in stars.

• Unstable and short-lived in nature
• Integral to higher-element formation through further fusion

This fleeting existence of beryllium-8 illustrates a complex and intriguing aspect of nuclear fusion in stars, facilitating element formation beyond helium in the universe.