Physical Chemistry: Spectroscopy

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Questions and Answers

Explain how UV-Vis spectroscopy can be used to determine the concentration of a solution, and what law governs this relationship?

UV-Vis spectroscopy measures the absorbance of a solution at specific wavelengths. The concentration is determined using the Beer-Lambert Law, which states that absorbance is directly proportional to the concentration and path length of the light beam through the solution.

Describe the difference between an electrolytic cell and a galvanic cell in terms of spontaneity and energy conversion.

A galvanic cell is spontaneous and converts chemical energy into electrical energy. An electrolytic cell is non-spontaneous and requires an external electrical energy source to drive a non-spontaneous chemical reaction.

Explain how a catalyst increases the rate of a chemical reaction. Briefly describe the effect on both the forward and reverse reaction rates.

A catalyst increases the rate of a chemical reaction by providing an alternative reaction pathway with a lower activation energy. It increases the rates of both the forward and reverse reactions equally, without changing the equilibrium constant.

What is the physical significance of the wavefunction in quantum mechanics, and how is it related to probability?

The wavefunction describes the quantum state of a particle and contains all the information about the particle. The square of the magnitude of the wavefunction gives the probability density of finding the particle at a particular point in space. Signup and view all the answers

Explain the concept of entropy and its relationship to the spontaneity of a process. How does the second law of thermodynamics relate to this?

Entropy is a measure of the disorder or randomness of a system. The second law of thermodynamics states that the entropy of an isolated system tends to increase over time. A process is more likely to be spontaneous if it leads to an increase in the entropy of the system and its surroundings. Signup and view all the answers

How does the Nernst equation relate cell potential to non-standard conditions? Provide an example of a situation where using the Nernst equation would be crucial.

The Nernst equation relates the cell potential (E) to the standard cell potential (E°) and the reaction quotient (Q) considering temperature and the number of electrons transferred: $E = E° - (RT/nF)lnQ$. It's crucial when reactant/product concentrations deviate from standard conditions (1 M), significantly affecting the cell potential. Signup and view all the answers

Explain what is meant by the 'steady-state approximation' in chemical kinetics, and give a situation in which it is typically applied.

The steady-state approximation assumes that the concentration of a reactive intermediate in a reaction mechanism remains constant during the reaction. It is applied when the intermediate is consumed as quickly as it is formed, allowing simplification of the rate equations. Signup and view all the answers

Describe the significance of quantum numbers in defining the state of an electron in an atom. What information does each of the four quantum numbers provide?

Quantum numbers define the energy and spatial distribution of an electron. The four quantum numbers are: principal (n, energy level), azimuthal or angular momentum (l, orbital shape), magnetic (ml, orbital orientation), and spin (ms, electron spin). Signup and view all the answers

Explain the difference between state functions and path functions in thermodynamics, providing an example of each.

State functions depend only on the initial and final states of the system, not on the path taken (e.g., internal energy, enthalpy, entropy, Gibbs free energy). Path functions depend on the path taken between states (e.g., heat and work). Signup and view all the answers

Describe how infrared (IR) spectroscopy can be used to identify functional groups within a molecule.

IR spectroscopy measures the absorption of infrared radiation by molecules, causing vibrational excitations. Different functional groups absorb at characteristic frequencies, allowing their identification based on the peaks observed in the spectrum. Signup and view all the answers

Flashcards

Spectroscopy

Study of interaction between matter and electromagnetic radiation to identify, quantify, and study molecular structure.

Absorption Spectroscopy

Measures radiation absorption versus frequency or wavelength.