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
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).
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.