Physical Chemistry: Scales, Approaches, and Topics

• Physical Chemistry is the study of matter's physical and chemical characteristics and properties.
• It uses physics to study chemical systems both qualitatively and quantitatively.

Chemical Property Scales

• Microscopic Scale: Involves observing properties using a microscope, such as the shape and structures of crystals.
• Macroscopic Scale: Deals with larger, observable behaviors like group behavior, melting point, or freezing point.
• Atomic Scale: Relates to elements, atomic mass, and atomic number.
• Subatomic Scale: Focuses on the number of protons, neutrons, and electrons.

Approaches to Studying Physical Chemistry

• Systematic Approach: Begins with fundamental particles and builds up to larger systems.
• Phenomenological Approach: Starts directly with macroscopic entities, such as large molecules.

Topics Under Physical Chemistry

• Thermodynamics
• Kinetics
• Quantum Mechanics
• Statistical Mechanics
• Spectroscopy
• Photochemistry

Matter and States of Matter

• Matter: Composed of subatomic particles like protons, neutrons, and electrons.
• Solids: Have a definite shape & volume, with tightly packed particles vibrating in a fixed position e.g. Ice, Wood, Stone
• Liquids: Have a definite volume but take the shape of their container, with close but mobile particles e.g. Water, Oil, Milk
• Gases: Take the shape and volume of their container, with particles that are far apart and move freely e.g. Air, Oxygen, Nitrogen

Quantifying Matter

• Includes understanding substance, amount of property, Avogadro's number, extensive & intensive properties, molar property, and molarity.

System, Universe, and Surroundings

• System: The part of the universe under observation.
• Boundary: Separates the system from its surroundings.
• Surroundings: Everything outside the system.
• Universe: The system plus the surroundings.
• Sign Conventions:
  • Endo: Indicates "into," e.g. Papasok.
  • Exo: Indicates "out of," e.g. Papalabas.

Types of Systems

• Open System: Exchanges both energy and mass with the surroundings.
• Closed System: Exchanges only energy with the surroundings.
• Isolated System: Exchanges neither energy nor mass with the surroundings.

Intensive and Extensive Properties

• Intensive Properties: Do not depend on the amount of matter e.g. temperature, boiling point, concentration.
• Extensive Properties: Depend on the amount of matter in a sample e.g. weight, length, volume.

State Functions and Variables

• State Functions: Properties dependent only on the initial and final states, regardless of the path taken; examples include enthalpy change and internal energy change.
• Variables:
  • Independent Variables: Specified values.
  • Dependent Variables: Change as known values are modified.
• Equilibrium: A state where there is no change with time.
• Equation of State: Relates different variables previously stated.

Thermal Equilibrium – Zeroth Law of Thermodynamics

• Thermal Equilibrium: Characterized by no difference in temperature between two or more bodies or systems.
• Application: The Zeroth Law is applied using thermometers to achieve Thermal Equilibrium with what is being measured.

Criteria for Equilibrium

• Thermal Equilibrium: Defined by equal temperature for different bodies.
• Mechanical Equilibrium: Defined by equal mechanical properties such as pressure.
• Chemical Equilibrium: Defined by constant chemical composition.

Energy and Work

• Energy: Defined as the capacity to do work or heat. Potential and kinetic energy are examples.
• Work: Causes mechanical displacement on a body. Work = Force x displacement (N*m)
• Units of Work: Joule, Calorie (energy to heat 1g of water by 1°C), Kcal.

Characteristics of Gases

• Expansibility: Gases expand to fill their entire container.
• Compressibility: Gases can be compressed with the application of pressure.
• Diffusibility: Gases diffuse rapidly and mix to form a homogenous mixture.
• Pressure: Gases exert pressure from collisions with the container.

Parameters of Gases

• Volume: Is the same as the volume of their container, 1 dm^3 = 1 L, 1 mL = 1 cm^3
• Pressure: Defined as Force/Area:
  • 1 Pa = 1 N/m^2
  • 1 Pa = 1 kg/m s^2
• Gases exert steady pressure.
• Pressure head = pgh

Manometers

• Manometers measure pressure based on liquid levels in a U-shaped tube.

Perfect (Ideal) Gas

• Gases are made of molecules.
• These molecules are in constant, random motion, colliding with each other and the container.
• All collisions are perfectly elastic meaning there is no energy loss.
• Absolute temperature is proportional to the KE of the molecules.
• Attractive forces between the molecules are negligible due to large distance.
• The volume of the molecules is negligible to the total volume of the gas.

Ideal Gas and Ideal Gas Equation

• Ideal gas favors vaporization.
• It favors low pressure and high temperature.
• PV = nRT

Gas Laws

• Some Gas Laws include:
  • Boyle's Law
  • Charles' Law
  • Gay-Lussac's Law
  • Avogadro's Law

Other Ideal Gas Law Forms

• Other equations can be derived from the base Ideal Gas Law equation
• Derived equations can solve for density, MW and other possible variables.

Different Standards for Temperature and Pressure

• Standard Temperature and Pressure (STP): 273 K (0°C) and 1 atm (760 mm Hg); one mole of gas occupies 22.4 liters.
• Standard State Conditions: Used for thermodynamic calculations:
  • The standard state temperature is 25°C (298 K)
  • All gases are at 1 atm pressure
  • All liquids and gases are pure
  • All solutions are at 1M concentration
  • The energy of formation of an element in its normal state is defined as zero.
• Normal Temperature and Pressure (NTP): Defined for air at 20°C (293.15 K, 68 degrees F) and 1 atm.
• International Standard Atmosphere (ISA): Defined for 101.325 kPa, 15°C, and 0% humidity.
• ICAO Standard Atmosphere: Defined for atmospheric pressure of 760 mm Hg and a temperature of 15 degrees C (288.15 K or 59 degrees F).

Definitions Constant Parameters

• Isochoric: Constant Volume.
• Isobaric: Constant Pressure.
• Isothermal: Constant Temperature.
• Isentropic: Constant Entropy.

Dalton's Law of Partial Pressures

• In a gas mixture, each gas exerts a pressure as if it were alone in the container.
• The Individual Pressure of each gas in the mixture is defined as its Partial Pressure.
• The total pressure is the sum of the partial pressures.

Amagat's Law of Partial Volumes

• The volume of a gas mixture is equal to the sum of the volumes of each component gas, if the temperature and pressure remain the same.

Dalton's Law vs. Amagat's Law

• Dalton's Law: Assumes gases are non-interacting; each gas independently applies its own pressure, summing to the total pressure.
• Amagat's Law: Assumes volumes are additive, with consistent interactions among different gases.

Graham's Law of Diffusion

• When two gases are placed in contact, they mix spontaneously called Diffusion.
• Molecules with smaller masses diffuse faster than heavier ones.

Graham's Law of Effusion

• When a gas escapes through a pinhole into a vacuum (Effusion), its rate depends on the molecular mass of the gas.