General Chemistry for Engineers CHEN 1201 Study Notes - 37

General Information

  • Course: General Chemistry for Engineers (CHEN 1201)

  • Instructor: Carolyn Kohlmeier

  • Department: Chemical and Biological Engineering

Week 14 Lecture Summary

Lecture 37 Overview

  • Topics Covered:

    1. Intermolecular forces

    2. Surface tension and capillary action

    3. Vapor pressure

  • Today's Focus:

    1. Heating Curves

    2. Phase diagrams

Vapor Pressure Comparison

Problems Involving Vapor Pressure

  • Compare the vapor pressures of the following substances at a given temperature:

    • SF6, SiH4, SF4

  • Possible Orderings:
    A. SF6 < SiH4 < SF4
    B. SF4 < SF6 < SiH4
    C. SiH4 < SF4 < SF6
    D. SiH4 < SF6 < SF4

  • Geometry Considerations:

    • SF6 (sulfur hexafluoride) and SF4 (sulfur tetrafluoride) geometries are essential for comparison.

Boiling Point Scenario

Pressure and Boiling Point

  • Given a figure indicating the boiling point of diethyl ether at an external pressure of 0.605 atm, the boiling point in °C is to be determined:
    A. 40
    B. 10
    C. 30
    D. 20
    E. 65

Heating Curves Overview

Key Concepts

  • Visual Representation of Heat Changes

  • Heat Added (kJ/mol) vs Temperature (°C)

  • Important Phases:

    • Ice

    • Water

    • Steam

  • Conditions illustrate water at P = 1 atm

Process of Heat Transfer

Example Problem: Heat Calculation

  • Scenario: Calculate heat released when transitioning from steam at 100.0°C to ice at -15.0°C with a mass of 75.0 g

  • Relevant Data:

    • Enthalpy of vaporization (ΔHvap) = 40.67 kJ/mol

    • Enthalpy of fusion (ΔHfus) = 6.01 kJ/mol

    • Molar heat capacity of liquid water = 75.4 J/(mol °C)

    • Molar heat capacity of ice = 36.4 J/(mol °C)

Calculation Formula

  • General heat calculation formula:
    q = [- ext{ΔH}{vap} + C{AT} - ext{ΔH}{fus} + C{AT}]n

Detailed Example with Numerical Calculation

  • When calculating:

    • q = -[-40.67 ext{ kJ} + 175.4 ext{ J} imes n]

    • Accounting for temperature changes and specific heat capacities leads to:

    • q = -227.8 ext{ kJ}

CO2 Phase Diagram

Questions and Key Points

  • Identify the minimum pressure for the existence of liquid CO2

  • Determine the critical pressure of CO2

  • Outcome of reducing pressure from 72 atm to 5.0 atm at 28°C

State Post-Phase Change

  • At conditions of 0 °C and 0.10 atm, when CO2 is compressed until a phase change occurs, determine the final state:
    A. Gas
    B. Liquid
    C. Solid
    D. Supercritical fluid

Phase Diagrams and Heating Curve Relationship

Heating Curve Representation

  • Influences of Pressure on Phase Changes

  • Temperature & Pressure interactions illustrated in heating curves

Water Phase Diagram Insights

Unusual Properties of Water

  • Phase behavior under varying pressures:

    • Effect of increasing pressure from atmospheric to 800 atm at about –5°C

    • Noteworthy Characteristic: The melting line of water has a negative slope

    • Unique Property: Ice is less dense than water, which significantly impacts phase transitions.