Question

Point out the correct statement: (1) Tritium is formed continuously in nuclear reactions induced by cosmic rays. (2) Deuterium is non-radioactive in contrast to tritium (3) The kinetic study of reaction rates show in many cases, so called isotopic effect in which hydrogen reacts faster than deuterium. (4) The para forms of both \(\mathrm{H}_{2}\) and \(\mathrm{D}_{2}\) are stable at low temperature while the ortho forms are stable at higher temperatures. (a) \(1,2,3\) (b) \(1,2,4\) (c) \(2,3,4\) (d) 2,4

Short answer

Option (c) \(2, 3, 4\) is correct.

Step-by-step solution

Analyze Statement 1

Tritium is a radioactive isotope of hydrogen and is formed in the upper atmosphere by nuclear reactions involving cosmic rays with atmospheric gases such as nitrogen and oxygen. Therefore, Statement 1 is correct.

Analyze Statement 2

Deuterium is a stable, non-radioactive isotope of hydrogen whereas tritium is radioactive. This means that in contrast to tritium, deuterium does not undergo radioactive decay. Therefore, statement 2 is correct.

Analyze Statement 3

The isotopic effect refers to the change in reaction rate due to the presence of different isotopes. It is well-known in chemical kinetics that reactions involving lighter isotopes such as hydrogen tend to proceed faster than those involving heavier isotopes like deuterium. Therefore, statement 3 is correct.

Analyze Statement 4

The para and ortho forms of molecular hydrogen differ in their nuclear spin states. The para form is more stable at lower temperatures while the ortho form is favored at higher temperatures. This is true for both regular hydrogen (8160_{2}81620) and deuterium (8160_{2}^{1681620}). Thus, statement 4 is correct.

Determine the Correct Options

Since statements 1, 2, 3, and 4 are all correct, we evaluate the given options. Option (a) contains statements 1, 2, and 3, which are correct. Option (b) contains statements 1, 2, and 4, which are correct but not complete since statement 3 is also correct and missing here. Option (c) contains statements 2, 3, and 4, all of which are correct. Option (d) contains only statements 2 and 4. Therefore, the correct option is (c).

Key concepts

Tritium and Cosmic Rays

Tritium, denoted as \(^3H\), is a radioactive isotope of hydrogen. It is formed naturally in the Earth's atmosphere by the action of cosmic rays. Cosmic rays are high-energy particles originating from outer space. When these rays enter the Earth's atmosphere, they can collide with atmospheric gases such as nitrogen and oxygen. In these interactions, neutrons are produced, which then react with nitrogen to form tritium through a nuclear reaction. This continuous formation of tritium through cosmic-ray interaction ensures a natural abundance of this isotope, despite its radioactive nature. Its formation process is an interesting example of how extraterrestrial forces can influence terrestrial phenomena.

Deuterium Stability

Deuterium, represented as \(^2H\), is another isotope of hydrogen. Unlike tritium, deuterium is non-radioactive, meaning it does not undergo radioactive decay. This stability is critical in various applications, such as in nuclear reactors, where deuterium is used as a moderator to slow down neutrons. It is twice as heavy as regular hydrogen due to the extra neutron in its nucleus, but its non-radioactive nature makes it safer to handle compared to tritium. While tritium's radioactivity limits its use, deuterium's stability allows for broader applications in scientific and industrial processes without concerns about radiation damage.

Reaction Rates and Isotopes

The isotopic effect describes how the presence of different isotopes can influence chemical reaction rates. Specifically, in reactions involving hydrogen isotopes, these effects are pronounced. Hydrogen, being the lightest isotope, typically reacts faster than its heavier counterpart, deuterium. This difference in reaction rate is due to the lower mass of hydrogen, which results in weaker bonds and a higher kinetic energy at a given temperature. In chemical kinetics, these kinetic isotope effects are crucial for understanding reaction mechanisms and are utilized in fields ranging from biochemistry to materials science. It illustrates how mass and nuclear properties of isotopes significantly affect how chemical reactions occur.

Para and Ortho Hydrogen Forms

Hydrogen molecules both \(H_2\) and \(D_2\) exist in two spin isomeric forms, para and ortho. These forms are distinguished by the spins of their atomic nuclei. Para hydrogen has antiparallel nuclear spins, while ortho hydrogen has parallel spins. This difference results in distinct stability profiles at varying temperatures. The para form is more stable at low temperatures, whereas the ortho form is preferred at higher temperatures. This variation is due to the quantum mechanical properties of the molecules, influencing their rotational and vibrational states. Understanding the behavior of para and ortho hydrogen is essential in low-temperature physics and chemistry, as it affects a variety of applications including rocket fuel performance and hydrogen storage technologies.