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 (A)

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 (B)</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 (A)</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 (A)</p> Signup and view all the answers

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

<p>True (A)</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 (D)</p> Signup and view all the answers

Photochemical reactions primarily occur in the absence of light.

<p>False (B)</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.

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What is the formula for calculating transmission?

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

The absorbance increases when transmission increases.

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

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

<p>False (B)</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. (C)</p> Signup and view all the answers

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

<p>False (B)</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. (A)</p> Signup and view all the answers

The presence of light has no effect on photochemical reactions.

<p>False (B)</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 (B)</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 (B)</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

Flashcards

Collision Theory: How does collision frequency affect reaction rate?

The rate of a chemical reaction is directly proportional to the collision frequency. The higher the collision frequency, the faster the reaction.

Collision Theory: What is required for a reaction to occur?

Not all collisions lead to reactions. For a reaction to occur, molecules must collide with enough energy and the correct orientation.

Activation Energy (Ea)

The minimum energy required to start a chemical reaction.

Activated Complex (Transition State)

A temporary, unstable species formed when reactant molecules collide before forming products.

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Exothermic Reaction

A reaction that releases heat into the surroundings.

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Endothermic Reaction

A reaction that absorbs heat from the surroundings.

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Arrhenius Equation

The relationship between the rate constant (k) of a reaction and temperature, showing that the rate constant increases exponentially with temperature.

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Frequency Factor (A)

A constant that represents the frequency of collisions between reactant molecules, independent of temperature.

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How does temperature affect the rate constant?

The dependence of the rate constant of a reaction on temperature can be expressed by the Arrhenius Equation.

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Catalyst

A substance that increases the rate of a reaction but is not consumed by the reaction.

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Homogeneous Catalyst

A catalyst that exists in the same phase (or state) as the reactants.

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Heterogeneous Catalyst

A catalyst that exists in a different phase than the reactants. Often a solid surface providing a reaction site.

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Enzymes

Biological catalysts, usually large protein molecules with specific active sites where reactions occur.

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Active Site

The specific region on an enzyme where the substrate (reactant molecule) binds.

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Substrate

A reactant molecule that binds to the active site of an enzyme.

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Enzyme-Substrate Binding. How does it affect rate?

The process where an enzyme binds to a substrate to lower the activation energy, speeding up the reaction.

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Elementary Reaction

A sequence of individual steps that make up an overall chemical reaction. Each step involves the collision of molecules.

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Rate Law

The rate law for a chemical reaction describes how the rate of the reaction depends on the concentration of the reactants.

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Rate-determining step (RDS)

A reaction where the rate is determined by the slowest step in the reaction mechanism.

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First-order Reaction

A reaction where the rate is proportional to the concentration of only one reactant raised to the first power.

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Second-order Reaction

A reaction where the rate is proportional to the product of the concentrations of two reactants, each raised to the first power.

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Second-order Reaction

A reaction where the rate is proportional to the square of the concentration of one reactant.

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Higher-order Reaction

A reaction where the rate is proportional to the product of the concentrations of three or more reactants.

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Concentration Effect

The change in the rate of a reaction that results from altering the concentration of the reactants.

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Zero-order Reaction

A reaction where the rate is independent of the concentration of the reactants.

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Reaction Mechanism

A reaction mechanism that consists of one or more elementary reactions. Each step involves the formation of a temporary intermediate before forming the final product.

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Intermediate

A species formed in a reaction step before the formation of the final product.

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Unimolecular Reaction

A mechanism that involves a single reactant molecule reacting to form a product.

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Bimolecular Reaction

A mechanism that involves the collision of two reactant molecules.

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Termolecular Reaction

A mechanism involves the collision of three molecules to form a product.

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Rate-determining step (RDS)

The overall rate of a reaction is determined by the slowest step in the mechanism.

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Photochemical Reaction

A chemical reaction that involves the absorption of light energy to trigger a change in the chemical structure of a substance.

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Photosynthesis

A type of photochemical reaction that is essential for life on Earth. It involves the conversion of carbon dioxide and water into sugars and oxygen using sunlight.

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Electromagnetic Spectrum

The range of all electromagnetic radiation, from low energy radio waves to high energy gamma rays.

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Photon

The smallest unit of light energy, also known as a quantum of light.

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Frequency of Light

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

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Wavelength of Light

The distance between two successive crests or troughs of a wave.

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Thermochemical Reaction

A reaction that involves the absorption or release of heat energy, without the involvement of light.

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Enthalpy Change

The difference in energy content between reactants and products.

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Transmission (T)

The fraction of light that passes through a sample and reaches a detector.

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Absorbance (A)

A quantitative measure of how much light is absorbed by a sample at a specific wavelength.

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Beer-Lambert Law

A relationship that describes the relationship between absorbance, concentration, path length, and molar absorptivity.

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Molar Absorptivity (ε)

The amount of light absorbed by a substance at a specific wavelength.

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Path Length (b)

The distance that light travels through the sample.

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Spectrophotometry

The study of the absorption and emission of light by molecules. Used to identify and quantify substances.

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Photoexcitation

The process by which a molecule absorbs a photon of light and is raised to an excited electronic state.

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Quantum Yield (Φ)

The ratio of the number of molecules that undergo a photochemical reaction to the number of photons absorbed.

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Quantum Yield Ranges

When one molecule is decomposed for every photon absorbed, the quantum yield is 1. If more than one molecule is changed per photon, the quantum yield is greater than 1, indicating high efficiency. If less than one molecule is changed per photon, the quantum yield is less than 1 indicating low efficiency.

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Energy of a Photon (∈)

The energy of a photon (or quantum), denoted as ∈, is directly proportional to its frequency (v) and inversely proportional to its wavelength (λ).

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One Einstein

One einstein represents the energy of an Avogadro's number of photons. It's the amount of energy associated with a mole of photons.

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Einstein and Wavelength

The energy of one einstein is inversely proportional to the wavelength of radiation. Longer wavelengths carry less energy per einstein.

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Calculating Einstein Energy (E)

The energy of one einstein (E) can be calculated using the equation E = (2.859 x 10^5)/λ kcal mol-1, where λ is the wavelength of radiation in Angstroms (Å).

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Threshold Energy for Photochemical Reactions

The amount of energy required to start a photochemical reaction. It's the minimum energy that a photon must have to break the bonds of reactants.

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Photochemistry

The study of chemical reactions initiated by the absorption of light.

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Energy of a photon

The energy carried by a single photon, which is directly proportional to its frequency and inversely proportional to its wavelength.

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Energy per einstein

The energy associated with a mole of photons, calculated by multiplying the energy of a single photon by Avogadro's number.

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Quantum yield

The ratio of the number of molecules that undergo a photochemical reaction to the number of photons absorbed. A measure of the efficiency of a photochemical process.

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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/Kâ‹…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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