Problem 51 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is a fusion reaction? (a) \({ }_{98} \mathrm{U}^{235}+{ }_{0} \mathrm{n}^{1} \longrightarrow{ }_{56} \mathrm{Ba}^{141}+{ }_{36} \mathrm{Kr}^{92}+3_{0} \mathrm{n}^{1}\) (b) \({ }_{92} \mathrm{Fe}^{239}+{ }_{0} \mathrm{n}^{1} \longrightarrow{ }_{92} \mathrm{U}^{239}+\mathrm{Y}\) (c) \({ }_{26} \mathrm{Fe}^{55}+{ }_{-1} \mathrm{e}^{0} \longrightarrow{ }_{25} \mathrm{Mn}^{55}\) (d) \({ }_{1} \mathrm{H}^{1}+{ }_{1} \mathrm{H}^{1}+2{ }_{0} \mathrm{n}^{1} \longrightarrow{ }_{2} \mathrm{He}^{4}+\) energy

Step-by-Step Solution

Answer

Option (d) is the fusion reaction.

Step 1: Understand the Definition

Fusion reactions involve two light atomic nuclei combining to form a heavier nucleus, typically releasing energy. This is different from fission reactions, where a heavy nucleus splits into lighter nuclei.

Step 2: Evaluate Option (a)

Option (a) involves the reaction \({ }_{98} \mathrm{U}^{235}+{ }_{0} \mathrm{n}^{1} \longrightarrow{ }_{56} \mathrm{Ba}^{141}+{ }_{36} \mathrm{Kr}^{92}+3_{0} \mathrm{n}^{1}\). This is a fission reaction, as it involves the splitting of uranium, a heavy nucleus, into lighter nuclei.

Step 3: Evaluate Option (b)

Option (b) shows the reaction \({ }_{92} \mathrm{Fe}^{239}+{ }_{0} \mathrm{n}^{1} \longrightarrow{ }_{92} \mathrm{U}^{239}+\mathrm{Y}\). This is another form of nuclear reaction, likely transmutation or capture, but not a fusion reaction as it does not involve two light nuclei producing a heavier one.

Step 4: Evaluate Option (c)

Option (c) describes the reaction \({ }_{26} \mathrm{Fe}^{55}+{ }_{-1} \mathrm{e}^{0} \longrightarrow{ }_{25} \mathrm{Mn}^{55}\). This is a beta decay process, not a fusion reaction since it does not involve merging light nuclei to form a heavier nucleus.

Step 5: Evaluate Option (d)

Option (d) involves the reaction \({ }_{1} \mathrm{H}^{1}+{ }_{1} \mathrm{H}^{1}+2{ }_{0} \mathrm{n}^{1} \longrightarrow{ }_{2} \mathrm{He}^{4}+\) energy. This reaction shows two hydrogen nuclei (protons) combining to form a helium nucleus, releasing energy, which is a characteristic of fusion reactions.

Key Concepts

Fission Reactions

Fission reactions are a type of nuclear reaction where a heavy atomic nucleus splits into two or more smaller nuclei. These reactions release a significant amount of energy, which is why they are often used in nuclear power plants to generate electricity. In a typical fission reaction, a heavy nucleus such as uranium-235 absorbs a neutron and becomes unstable.
The unstable nucleus then splits into lighter elements and additional neutrons. For instance, in the reaction \[{}_{98} \mathrm{U}^{235}+{}_{0} \mathrm{n}^{1} \longrightarrow{}_{56} \mathrm{Ba}^{141}+{}_{36} \mathrm{Kr}^{92}+3{}_{0} \mathrm{n}^{1}\] the uranium-235 nucleus absorbs a neutron and divides into barium-141, krypton-92, and three more neutrons.

• Releases Neutrons: Fission reactions release additional neutrons which can trigger further fission reactions in a chain reaction.
• Produces Energy: The splitting of the nucleus releases energy because of the conversion of mass into energy (as per Einstein's equation \(E=mc^2\)).
• Safety Concerns: Controlling these reactions safely is crucial, as uncontrolled reactions can lead to nuclear accidents.

Understanding fission reactions helps us explore nuclear energy as an alternative to fossil fuels.

Nuclear Reactions

Nuclear reactions refer to processes that change the structure of an atom's nucleus and often involve changes in energy. Unlike chemical reactions, which involve electrons, nuclear reactions involve the nucleons—protons and neutrons—in the nucleus of an atom. There are several types of nuclear reactions, including fusion, fission, and radioactive decay.
Characteristics of nuclear reactions:

• Mass and Energy: These reactions may involve the conversion of mass into energy, releasing or absorbing vast amounts of energy compared to chemical reactions.
• Isotope Production: Nuclear reactions can result in the formation of new isotopes, sometimes transforming one element into another.
• Application: Used in medicine, energy production, and research to understand fundamental physics.

Option (b) in our example with \[{}_{92} \mathrm{Fe}^{239}+{}_{0} \mathrm{n}^{1} \longrightarrow{}_{92} \mathrm{U}^{239} + Y\] is indicative of a nuclear reaction where the nucleus captures a neutron to become another uranium isotope. Understanding nuclear reactions allows us to harness their power and manage their implications effectively.

Beta Decay

Beta decay is a type of radioactive decay where a beta particle is emitted from an atomic nucleus. This process results in the transformation of a neutron into a proton or vice versa, and is categorized into beta-minus \((\beta^- )\) and beta-plus \((\beta^+ )\) decay.
In beta-minus decay, a neutron turns into a proton, emitting an electron and an antineutrino. In contrast, beta-plus decay involves a proton changing into a neutron, releasing a positron and a neutrino.Option (c) in our exercise represents a beta decay:\[{}_{26} \mathrm{Fe}^{55}+{}_{-1} \mathrm{e}^{0} \longrightarrow{}_{25} \mathrm{Mn}^{55}\] Here, a neutron in the iron nucleus is transformed into a proton, changing the element into manganese.Key points about beta decay:

• Elementary Particles: Emission of beta particles, which are high-energy, high-speed electrons or positrons.
• Element Transformation: Changes the identity of an atom, resulting in a new element.
• Radioactive Series: Plays a crucial role in the decay series of various radioactive isotopes.

Learning about beta decay aids in understanding the stability and transformation processes of atomic nuclei.