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Ch.6 - Electronic Structure of Atoms
Brown - Chemistry: The Central Science 15th Edition
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970Non è quello che usi tu?Cambia libro di testo
Capitolo 6, Problema 49

Neutron diffraction is an important technique for determining the structures of molecules. Calculate the velocity of a neutron needed to achieve a wavelength of 1.25 Å. The mass of a neutron is 1.675×10−27 kg.

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Identify the relationship between velocity, wavelength, and mass using the de Broglie equation: \( \lambda = \frac{h}{mv} \), where \( \lambda \) is the wavelength, \( h \) is Planck's constant (\( 6.626 \times 10^{-34} \) Js), \( m \) is the mass, and \( v \) is the velocity.
Rearrange the de Broglie equation to solve for velocity \( v \): \( v = \frac{h}{m\lambda} \).
Substitute the given values into the equation: \( h = 6.626 \times 10^{-34} \) Js, \( m = 1.675 \times 10^{-27} \) kg, and \( \lambda = 1.25 \times 10^{-10} \) m (since 1 Å = 1 \(\times\) 10^{-10} m).
Calculate the velocity \( v \) by performing the division: \( v = \frac{6.626 \times 10^{-34}}{1.675 \times 10^{-27} \times 1.25 \times 10^{-10}} \).
Ensure the units are consistent and simplify the expression to find the velocity of the neutron.

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De Broglie Wavelength

The De Broglie wavelength is a fundamental concept in quantum mechanics that relates the wavelength of a particle to its momentum. It is given by the formula λ = h/p, where λ is the wavelength, h is Planck's constant, and p is the momentum of the particle. For a neutron, the momentum can be expressed as p = mv, where m is the mass and v is the velocity. This relationship is crucial for understanding how particles like neutrons exhibit wave-like properties.
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Planck's Constant

Planck's constant (h) is a fundamental physical constant that plays a central role in quantum mechanics. It has a value of approximately 6.626 × 10^-34 Js and is used to describe the quantization of energy levels in atoms and the wave-particle duality of matter. In the context of neutron diffraction, it is essential for calculating the wavelength of neutrons based on their momentum, thereby linking classical and quantum physics.
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Kinetic Energy and Velocity

The kinetic energy of a particle is the energy it possesses due to its motion, expressed as KE = 0.5mv², where m is the mass and v is the velocity. In neutron diffraction, the velocity of the neutron is directly related to its kinetic energy and is essential for determining the appropriate conditions for achieving a specific wavelength. Understanding this relationship allows for the calculation of the velocity needed to produce a desired wavelength in neutron scattering experiments.
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Kinetic Energy Formulas