class 4 2025

• Advocacy Services Offered: Advice on rights, university procedures, and tenancy.

• Encouragement for students to vote for Class Representatives.

• Contact Information: Location: Old Choral, Alfred St, City Campus; Phone: 09 923 7294; Website: www.AUSA.ORG.NZ; Email: advocacy@ausa.org.nz

Partial Pressure and Dalton’s Law

• Key Concepts: Gases mix homogeneously in any proportions. Mole Fraction: The ratio of the partial pressure of a gas to the total pressure. Partial Pressure: Pressure exerted by a single gas in a gas mixture.

• Formula: P_total = P_A + P_B. Definition: Total pressure of a mixture of non-reacting gases equals the sum of the pressures each gas would exert individually in the same volume and temperature. Formula: P_total = P_gas A + P_gas B + P_gas C + ...

Calculating Partial Pressure

• To Calculate Partial Pressure: Use: Partial pressure of B = (mole fraction of B) × (total pressure of mixture).

• Example: Total pressure = 1.5 atm; Mole fractions: A = 3/9 = 1/3, B = 6/9 = 2/3; Partial Pressure of B = (2/3) × (1.5 atm) = 1.0 atm

Class 4 - Phase Changes

• Discussion Topic: Making a diamond from graphite.

• Covered the Kinetic Theory of Matter relating microscopic properties (temperature, pressure) to measurable properties. Current Class Focus: Understanding phase changes.

Learning Outcomes - Phase Changes

• Define phase, states of matter, and phase transition. Describe changes at each phase transition.

• Instructor: Dr. Marie-Anne Thelen (marie-anne.thelen@auckland.ac.nz)

Defining a Phase

• Properties: Chemically and physically uniform. A distinct, homogeneous part of a system. Common phases: solid, liquid, gas, supercritical fluids.

Phases vs. States of Matter

• Differences: Different phases can exist within the same state of matter (e.g., graphite vs. diamond). Phase of Matter: Uniform properties. State of Matter: Could have multiple phases with varying properties.

Phase Transition and Thermal Energy

• Process Defined: Phase transition is a change in phase without altering chemical composition. Occurs at specific pressures and temperatures (e.g., boiling and freezing points).

Thermal Energy Explained

• Definition: Energy transfer due to differences in kinetic or potential energy between particles. Kinetic energy: Related to particle motion. Potential energy: Related to position of particles.

Heating and Equilibrium

• Temperature remains constant until phase change is complete (solid to liquid or liquid to solid). Enthalpy of Fusion: Energy required to turn solid into liquid. Enthalpy of Vaporization: Energy required for liquid to gas.

• Analyzed energy changes during phase changes and conditions for phase coexistence in class activities.

• Discussed cooking rice at high altitude and the impact on boiling points.

• Explained the concept of Triple Point and Supercritical Fluids in food processing and their unique properties.

Summary of Phase Changes

• Defines phase and phase transition and summarizes how phase diagrams illustrate stable phase regions under varying pressures and temperatures.

Learning Outcomes - Phase Changes

1. Define Phase, States of Matter, and Phase Transition

   • Phase: A distinct, homogeneous part of a system, chemically and physically uniform. Common phases include solid, liquid, gas, and supercritical fluids.

   • States of Matter: Different phases can exist within the same state of matter (e.g., graphite vs. diamond). The phase has uniform properties, while the state may contain multiple phases with varying properties.

   • Phase Transition: A change in phase without altering the chemical composition, occurring at specific pressures and temperatures (e.g., boiling and freezing points).

2. Describe Changes at Each Phase Transition

   • Solid to Liquid: Melting; requires energy input (Enthalpy of Fusion).

   • Liquid to Gas: Vaporization; requires energy input (Enthalpy of Vaporization).

   • Gas to Liquid: Condensation; energy is released.

   • Liquid to Solid: Freezing; energy is released.

   • Solid to Gas: Sublimation; requires energy input.

   • Gas to Solid: Deposition; energy is released.