Pharmaceutical Analytical Chemistry I - Lecture 10
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Questions and Answers

What is the rate law for the reaction: aA + bB → products?

Rate = k[A]a[B]b

Reaction rates generally increase with increasing temperature.

True

What is the effect of storing foods at sub-zero temperatures?

It slows down the rate of bacterial decay.

The collision theory states that every collision between reactants leads to a product formation.

<p>False</p> Signup and view all the answers

What is the minimum amount of energy required to initiate a chemical reaction called?

<p>Activation energy</p> Signup and view all the answers

What is the state of a reaction when the products are less stable than the reactants?

<p>Endothermic reaction</p> Signup and view all the answers

What is the equation that describes the dependence of the rate constant on temperature?

<p>Arrhenius equation</p> Signup and view all the answers

What is the term for a substance that increases the rate of a chemical reaction without being consumed?

<p>Catalyst</p> Signup and view all the answers

What type of catalysis occurs when the catalyst exists in the same phase as the reactants?

<p>Homogeneous catalysis</p> Signup and view all the answers

What type of catalysis occurs when the catalyst exists in a different phase than the reactants?

<p>Heterogeneous catalysis</p> Signup and view all the answers

Enzymes are biological catalysts that increase the rate of biochemical reactions.

<p>True</p> Signup and view all the answers

What is the specific region on an enzyme where the substrate binds?

<p>Active site</p> Signup and view all the answers

How does sucrase affect the breakdown of sucrose?

<p>Sucrase catalyzes the breakdown of sucrose into glucose and fructose.</p> Signup and view all the answers

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What is the quantum yield of the reaction when 0.002 mole of substance A is reacted under the given conditions?

<p>5.00 × 10^11</p> Signup and view all the answers

The energy of a photon can be calculated using the formula ∈ = hv.

<p>True</p> Signup and view all the answers

How many photons are absorbed during the reaction if the quantum efficiency is 10.00 and 1x10^-4 mole of the substance is decomposed?

<p>6.02 × 10^18</p> Signup and view all the answers

The number of photons absorbed per second is given as ________ × 10^6.

<p>2.0</p> Signup and view all the answers

Match the following terms with their descriptions:

<p>Quantum yield = The ratio of the number of molecules reacted to the number of photons absorbed Quantum efficiency = The ratio of the number of molecules decomposed to the number of photons absorbed Photon = A particle representing a quantum of light Einstein = A mole of photons or a quantity of light expressed in moles</p> Signup and view all the answers

What year was Giacomo Luigi Ciamician born?

<p>1857</p> Signup and view all the answers

Photochemical reactions primarily occur in the absence of light.

<p>False</p> Signup and view all the answers

What is the main product of photosynthesis in plants?

<p>C6H12O6 (glucose)</p> Signup and view all the answers

The electromagnetic spectrum includes types of light such as gamma rays, x-rays, __________, visible light, infrared, __________, and radio waves.

Signup and view all the answers

What is the formula for calculating transmission?

<p>$T = \frac{I}{I_0}$</p> Signup and view all the answers

The absorbance increases when transmission increases.

<p>False</p> Signup and view all the answers

Calculate the absorbance of a solution with 50% transmission.

<p>0.301</p> Signup and view all the answers

According to the Stark-Einstein Law, one ______ decomposes one molecule.

<p>photon</p> Signup and view all the answers

Match the following laws of photochemistry with their definitions:

<p>Grothus-Draper Law = Only absorbed light causes a chemical reaction. Stark-Einstein Law = A molecule becomes excited by absorbing a single quantum of light.</p> Signup and view all the answers

What is the relationship between quantum yield and the number of molecules reacted?

<p>$Φ = \frac{No.of molecules reacted}{No.of photons absorbed}$</p> Signup and view all the answers

Cytosine's molar absorption coefficient is 6 x 10³ mol-1 cm¯¹ at all wavelengths.

<p>False</p> Signup and view all the answers

A photochemical reaction is initiated by the absorption of ______ by molecules.

<p>photons</p> Signup and view all the answers

What does a quantum yield (Φ) greater than 1 indicate?

<p>Two or more molecules are decomposed per photon.</p> Signup and view all the answers

The energy of a photon is directly proportional to its wavelength.

<p>False</p> Signup and view all the answers

What is Planck's constant (h) in erg-sec?

<p>6.624 × 10–27</p> Signup and view all the answers

The equation to calculate the energy of a photon is __ = hv.

<p>∈</p> Signup and view all the answers

Match the following equations with their descriptions:

<p>Φ = (No.of molecules decomposed) / (No.of photons absorbed) = Definition of quantum yield E = Nhc/λ = Energy of one einstein E = (1.196 x 1016)/λ erg mol-1 = Energy of photons in ergs E = (2.859 x 10^5)/λ kcal mol-1 = Energy of photons in kcal</p> Signup and view all the answers

If the quantum yield (Φ) is less than 1, what does that indicate?

<p>More photons are absorbed than necessary molecules are decomposed.</p> Signup and view all the answers

The energy of one einstein of photons is constant regardless of the wavelength.

<p>False</p> Signup and view all the answers

What is the relationship between the energy of a photon and its wavelength?

<p>Energy is inversely proportional to wavelength.</p> Signup and view all the answers

What is the primary characteristic that distinguishes photochemical reactions from thermochemical reactions?

<p>They involve the absorption of light.</p> Signup and view all the answers

The presence of light has no effect on photochemical reactions.

<p>False</p> Signup and view all the answers

Who is known as the 'Father of Modern Molecular Photochemistry'?

<p>Giacomo Luigi Ciamician</p> Signup and view all the answers

The overall equation for photosynthesis can be summarized as ______ + Light → C6H12O6 + 6O2.

<p>6CO2 + 6H2O</p> Signup and view all the answers

Which of the following wavelengths corresponds to visible light?

<p>10^-6 cm</p> Signup and view all the answers

Match the following types of light with their corresponding wavelength sizes:

<p>Gamma ray = 10^-12 cm X-ray = 10^-10 cm Ultraviolet = 10^-8 cm Infrared = 10^-4 cm</p> Signup and view all the answers

Temperature has a significant effect on the rate of photochemical reactions.

<p>False</p> Signup and view all the answers

What was Ciamician's first published experiment in photochemistry titled?

<p>On the conversion of quinone into quinol by light</p> Signup and view all the answers

Study Notes

Pharmaceutical Analytical Chemistry I - Lecture No. 10

  • Temperature and Rate: Reaction rates increase with temperature. The time needed for a reaction (like boiling an egg) is shorter at higher temperatures. Conversely, preserving food at sub-zero temps slows bacterial decay. Rate constant increases approximately doubling for every 10°C rise. Temperature significantly affects the rate of a reaction, changing the rate constant and, hence, the reaction rate.

  • Effect of Catalyst: A catalyst increases reaction rate but isn't consumed. It provides an alternative reaction mechanism with lower activation energy. This allows reactions to occur faster at lower temperatures. Catalysts play a key role in many biological processes and industrial reactions. Catalysts can react with reactants to form an intermediate, but they are regenerated in a subsequent step.

  • Collision Theory: Not every collision between molecules results in a reaction. For a successful reaction, molecules must collide with sufficient energy and the correct orientation. Many collisions occur, but not enough energy remains in the collision to cause a reaction to occur.

  • Activation Energy (Ea): The minimum energy required for a reaction to initiate an activation complex (a transition state). The activation energy governs reaction rates. Reactions with higher activation energies are significantly slower.

  • Arrhenius Equation: Describes the relationship between rate constant (k), activation energy (Ea), gas constant (R), and temperature (T). k = Ae^(-Ea/RT) where:

    • Ea is the activation energy (kJ/mol)
    • R is the gas constant (8.314 J/K⋅mol)
    • T is the absolute temperature (K)
    • A is the frequency factor (a constant for a given reaction and temperature range).

  • Homogeneous Catalysis: A catalyst in the same phase as the reactants. Examples include the catalytic destruction of ozone.

  • Heterogeneous Catalysis: A catalyst in a different phase compared to the reactants, often a solid surface. An example includes catalytic converters, where reactants are in a gas phase and the catalyst is a solid.

  • Enzymes: Biological catalysts (proteins). They have an active site that binds to a substrate molecule (reactant). This active site weakens bonds, lowering the activation energy, increasing reaction rate, and enabling reactions at lower temperatures. Enzymes are crucial for biological reactions.

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Description

This quiz covers key concepts from Lecture No. 10 in Pharmaceutical Analytical Chemistry I, focusing on the relationship between temperature and reaction rates, the role of catalysts, collision theory, and activation energy. Understand how these factors influence chemical reactions in both biological and industrial contexts.

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