CHE201 Final Term Subjective 2024 by VUBuddy

SUBJCTIVES OF CURRENT PAPER · CHE201 - Physical Chemistry · Final-Term File 2024 By · SULMAN ALI (BS-ZOOLOGY)

Differentiate between open, closed and isolated system?

The macroscopic part of the universe under study in thermodynamics is called the System. The parts of the universe that can interact with the system are called the surroundings. 1= Open system is one where transfer of matter between system and surroundings can occur.2= Closed system is one where no transfer of matter can occur between system and surroundings. 3= Isolated system is one that does not interact in any way with its surroundings. An isolated system is obviously a closed system, but not every closed system is isolated.

What are the properties of colloids?

•  Particle Size: Dispersant particles range from 1 nm to 500 nm in diameter.
•  Stability: Mixture does not separate under normal gravity.
•  Filtration: Cannot be filtered by common fiber filters.
•  Homogeneity: Usually close to homogeneous.
•  Tyndall Effect: Light scattering makes the pathway visible.
•  Saturation: No sharp saturation point.
•  Coagulation: Dispersant can clump with heat or ionic particles.
•  Colligative Properties: Minimal effect from dispersant.

Stopped-Flow Mechanism: short and long

The stopped-flow mechanism is a technique used to study solution-based kinetics on a millisecond timescale with minimal reactant volume. It involves two reactants in separate reservoirs that are mixed rapidly in a chamber by syringe pumps. The reaction is monitored by observing absorbance changes over time. The process is halted when the “stop syringe” fills and reaches a block, stopping the flow and reaction. This allows precise calculation of the initial reaction rate.

For example: For example, an enzyme catalyzed reaction can be stopped by adding an acid, base, or salt solution that denatures (destroys the activity of) the protein enzyme.

Elementary Steps for Reaction Mechanism:

Definition: Elementary steps are fundamental processes in a reaction mechanism explaining how the overall reaction proceeds.

The elementary steps used for mechanisms of chain reactions can be grouped into the following categories: 1= Initiation step, 2= Chain propagation steps, 3= Chain branching steps, 4= Chain inhibition steps, 5= Chain termination steps.

Types:

•  Unimolecular Step: Involves one molecule, first-order rate law.
•  Bimolecular Step: Involves two molecules, second-order rate law.
•  Trimolecular Step: Involves three molecules, third-order rate law.

Characteristics of Reaction Rate

Definition: Measures the change in concentration of reactants or products per unit time. Speed Variation: Reactions can be instantaneous or take years. Influencing Factors: Depends on the type of molecules and concentration levels. Examples: Fossilization is a slow reaction; some reactions happen in less than a second.

Phase and surface area effect on reaction rate:

Phase and surface area significantly impact reaction rates. Reactants in the same fluid phase collide more often, speeding up reactions. In heterogeneous reactions, where reactants are in different phases, collisions occur only at interfaces, reducing the rate. Increasing surface area, as in gasoline droplets, enhances reaction rates by increasing collision opportunities.

What are azeotrope?

•  An azeotrope is a mixture that exhibits the same concentration in the vapor phase and the liquid phase.
•  This is in contrast to ideal solutions with one component typically more volatile than the other; this is the reason we use distillation to separate materials.
•  If the mixture forms an azeotrope, the vapor and the liquid concentrations are the same, which preventing separation via this approach.
•  Azeotropes are a mixture of at least two different liquids.
•  Their mixture can either have a higher boiling point than either of the components or they can have a lower boiling point.
•  Azeotropes occur when fraction of the liquids cannot be altered by distillation.

Limitation of thermodynamics:

Thermodynamics has limitations in understanding reaction mechanisms and rates. Thermodynamics provides insight into the direction and equilibrium of chemical reactions by predicting free energy changes but does not address reaction rates or mechanisms. It tells us the final state but not how long it takes to reach equilibrium or the details of the reaction mechanism. Reaction rates and mechanisms must be studied experimentally, as they vary significantly even among similar reactions, as seen in the different mechanisms for the formation of hydrogen halides. Thus, thermodynamics alone cannot predict kinetic or mechanistic details.

Effect of Temperature and Pressure on Heat Capacity

Temperature: As temperature increases, specific heat capacity often rises because the added heat energy not only increases kinetic energy but also enables molecular vibrations and rotations. At lower temperatures, these modes are less accessible, so specific heat capacity is lower.

Pressure: Conventional thermodynamics suggests that heat capacity decreases with increasing pressure. However, model calculations show that heat capacity might increase, decrease, or remain unchanged depending on the model used.

Bomb Calorimeter vs. Ice Calorimeter

Bomb Calorimeter: Used for determining heats of combustion by combusting a sample in a fixed volume under high pressure. The process occurs in a vessel called a "bomb," and the reaction is ignited electrically. It measures the heat released during combustion.

Ice Calorimeter: Measures heat capacities and heats of reactions by observing the volume change due to ice melting. A warm sample is placed in an insulated chamber surrounded by ice and water. Heat loss causes ice to melt, and the resulting volume change in mercury provides the heat measurement.

The key difference is that the bomb calorimeter measures heat of combustion at constant volume, while the ice calorimeter measures heat capacities and reactions based on ice melting and volume change.

Explain when how enzymes decrease activations energy 5 marks

Enzymes decrease activation energy by providing an alternative reaction pathway with a lower energy transition state. As biological catalysts, enzymes bind to substrates and stabilize the transition state, reducing the energy required for the reaction to proceed. This results in a lower activation energy barrier, making it easier for reactants to collide and react. Consequently, the reaction rate increases in both the forward and reverse directions because less energy is needed for molecules to overcome the activation barrier. This increase in reaction rate is reflected in the higher rate constant (k).

Application of precipitation reaction:

Precipitation reactions are useful in determining whether a certain element is present in a solution. • If a precipitate is formed when a chemical reacts with lead, for example, the presence of lead in water sources could be tested by adding the chemical and monitoring for precipitate formation. • In addition, precipitation reactions can be used to extract elements, such as magnesium from seawater. • Precipitation reactions even occur in the human body between antibodies and antigens; however, the environment in which this occurs is still being studied.

Points of Maxwell distribution peak?

A sketch of a Maxwell distribution is given here.

•  The peaks are not symmetrical.
•  There are more molecules at higher speed than at lower speeds.
•  When the temperature increases, the peak shifts to the right. A more carefully plotted diagram is done

Which characteristics can be monitored for measurement of the rate of reaction?

1. Concentration: Changes in the concentration of reactants or products.
2. Pressure: Changes in pressure for gas-phase reactions.
3. Mass or Volume: Changes in mass or volume for reactions forming precipitates or gases.
4. pH: Changes in acidity or basicity.
5. Temperature: Changes in temperature.
6. Color: Changes in color, particularly observable through spectrophotometry.
7. Conductivity: Changes in conductivity for reactions involving ions.
8. Luminescence: Changes in light emission.
9. Reaction Kinetics: Direct observation of the rate of reactant consumption or product formation

What are the properties of lipids?

Lipids are hydrophobic or amphiphilic, storing energy efficiently, and forming cell membranes. They include fats, oils, and phospholipids. Lipids are insoluble in water but soluble in organic solvents, and they play key roles in cellular signaling and structure.

Application of kinetics energy:

•  Kinetic energy has various applications:
•  Transportation: Powers vehicles like cars, trains, and planes.
•  Sports: Athletes convert muscle energy into kinetic energy.
•  Industry: Used in machinery, conveyors, and assembly lines.
•  Renewable Energy: Wind turbines and hydroelectric plants harness kinetic energy.
•  Impact: Important in analyzing collisions and designing safer structures.
•  Projectile Motion: Determines velocity and range of projectiles in physics and engineering.

Describe Mass Percent, Volume Percent, Mass/Volume Percent:

1. Mass Percent: The mass percent is used to express the concentration of a solution when the mass of a solute and the mass of a solution is given: