15C+-+L3.3+-+Enthalpy+Cont%27d

Page 1

• Scientific Research by Rommie Amaro

  • Led a collaboration of 50 scientists to model COVID viruses in aerosol droplets at a molecular level.

  • Involved the modeling of 1.3 billion atoms together.

  • Created a virus model that included water in the aerosol and various compounds found in human lungs.

  • Utilized the second-largest supercomputer in the world for calculations.

Page 2

• This Week in CHEM 152 (Week 5: February 10-14)

  • Lecture Schedule:

    • Monday: Discussion Section Lab on Lecture 14: Enthalpy and Thermodynamics of Ideal Gases.

    • Wednesday: Lecture 15 on the same topics.

    • Friday: Lecture 16 covering Hess's Law, Heats of Formation, Solubility, Heat, and Work.

  • Discussion Section:

    • Collaborative assignments during scheduled meetings on Tuesdays or Thursdays.

  • Lab Information:

    • Consult Lab Canvas page for assignments details.

    • TAs and Prof. Carroll are the primary contact for lab-related queries.

  • Readings Due:

    • Lecture 14: Sections 9.2, 9.3.

    • Lecture 15: No reading assigned.

    • Lecture 16: Sections 9.4, 9.5, 9.6.

  • Active Reading Assignments:

    • Due at 11:00 AM on the day before each lecture.

  • ALEKS Modules:

    • Module 5 due February 10 at 11:59 PM.

    • Module 6 due February 18 at 11:59 PM.

Page 3

• Topics in Today's Lecture

  • Section 9.2: Enthalpy

  • Section 9.3: Thermodynamics of Ideal Gases

    • Heating an ideal gas at constant volume.

    • Heating an ideal gas at constant pressure.

    • Heating a polyatomic gas.

    • Energy relationship and enthalpy of gases.

Page 4

• Learning Goals for Today's Lecture

  • Calculate:

    • ΔT, ΔH, ΔE, and Δ(PV) under varying conditions.

  • Understand and define thermodynamic pathways.

  • Define:

    • Isobaric (constant pressure), isochoric (constant volume), and isothermal (constant temperature).

  • Perform calculations relating to these conditions.

Page 5

• Last Class Recap

  • Key Terms:

    • Work (wsys)

    • Internal Energy (E)

    • Enthalpy (H)

    • Heat capacities at constant pressure (qP) and constant volume (qV).

  • Formulas:

    • ( \Delta E = \frac{2}{5} nR \Delta T )

    • ( \Delta H = \frac{2}{5} nR \Delta T )

    • Work done on/by system: ( w = -\Delta P \Delta V )

Page 6

• Example Problem: Constant Pressure

  • Scenario: Volume of 0.75 mol of neon gas reduced from 10.0 L to 5.0 L at 0.85 atm.

  • Questions:

    1. Determine temperature change.

    2. Calculate ΔH.

    3. Determine ΔE.

    4. Find work done on/by the system.

  • Findings:

    • Process is exothermic; temperature decreased,

    • ΔH = -1076 J,

    • ΔE = -645 J,

    • Work done (w) = +430 J.

Page 7

• Example Problem: Constant Volume

  • Scenario: Pressure of 0.75 mol of neon gas increases from 0.50 atm to 1.27 atm in a constant volume of 10.0 L.

  • Tasks to determine:

    1. Temperature change.

    2. Calculate ΔH.

    3. Determine ΔE.

    4. Find Δ(PV).

Page 8

• Calculating Temperature Change

  • Method: ( \Delta T = \frac{P_f - P_i}{nR} )

  • Values used:

    • P_f = 1.27 atm,

    • P_i = 0.50 atm,

    • Volume = 10.0 L,

    • Moles = 0.75 mol,

  • Result: ( \Delta T = +125 K ).

Page 9

• Calculating ΔH

  • Formula used:

    • ( \Delta H = nC_P\Delta T )

  • Result: ( \Delta H = +1948 J ).

Page 10

• Calculating ΔE

  • Formula:

    • ( \Delta E = nC_V\Delta T )

  • Result: ( \Delta E = +1169 J ).

Page 11

• Calculating Δ(PV)

  • Note: PV work is defined as PΔV.

  • Result: ( \Delta(PV) = +780 J ).

Page 12

• Summary of Results

  • Process is endothermic; temperature increased:

    • ΔT = +125 K,

    • ΔH = +1948 J,

    • ΔE = +1169 J,

    • Δ(PV) = +780 J.

Page 13

• Measuring ΔE and ΔH

  • Constant Volume:

    • No PV work created.

    • Energy added increases internal energy (E).

  • Constant Pressure:

    • All added heat increases Enthalpy (H).

Page 14

• Thermodynamic Pathway Exploration

  • Example: 2.00 mol of an ideal monatomic gas undergoes a change from State A to State B:

    • State A: ( P_A = 2.00 atm, V_A = 10.0 L )

    • State B: ( P_B = 1.00 atm, V_B = 30.0 L )

  • The calculations for heat, work, ΔE, and ΔH are structured around varying pathways.

Page 15

• Understanding Thermodynamic Paths

  • Thermodynamic path involves a sequence of manipulations to transition from initial to final states.

  • Constants for different pathways:

    • Isochoric: Constant Volume

    • Isobaric: Constant Pressure

    • Isothermal: Constant Temperature

Page 16

• Choosing a Pathway

  • Goal: Transition from A to B.

    • Path 1: Expansion (A to C) followed by cooling (C to B).

    • Path 2: Cooling (A to D) followed by expansion (D to B).

Page 17

• Pathway 1, Step AC

  • Isobaric expansion from 10.0 L to 30.0 L at a steady 2.00 atm pressure.

  • Heat added calculated using the equation.

  • Result for heat added: ( q_{AC} = +10,130 J ).

Page 18

• Pathway 1: Work and ΔE

  • Work performed during expansion calculated and compared to ΔE.

  • Results:

    • Work done = -4052 J.

    • ΔE = +6078 J.

Page 19

• Pathway 1, Step CB

  • Isochoric decrease in pressure from -

  • Heat removed leads to a temperature decrease.

  • Calculated values for heat removed and ΔE obtained.

Page 20

• Consistency Check on Enthalpy and Energy

  • No work performed under constant volume.

  • Results validate through expanded calculations yielding consistent ΔH and ΔE.

Page 21

• Summary of Pathway 1 Results

  • Total values obtained indicate cumulative changes through each step across properties.

Page 22

• Pathway 2, Step AD

  • Isochoric decrease in pressure:

    • Similar conditions as Path 1, Step CB.

    • Heat removed with calculated results for ΔE obtained.

Page 23

• Pathway 2, Step DB

  • Isobaric expansion from 10.0 L to 30.0 L as in Pathway 1.

  • The same processes and calculations for work and ΔE evaluated.

Page 24

• Pathway 2 Results:

  • Calculations reaffirm the endothermic nature of the pathway with consistent results.

Page 25

• Pathway 2 Overview

  • Breakdown of work done and ΔE as compared to Pathway 1.

Page 26

• Comparative Analysis: Pathways 1 and 2

  • Examined overall changes in temperature, heat, work, ΔE, and ΔH across both paths.

Page 27

• Key Takeaways

  • Energy and Enthalpy are state functions (path independent).

  • Work and heat are process functions (path dependent).

Page 28

• Readings for Next Lecture

  • Sections 9.4, 9.5, 9.6 on:

    • Calorimetry and calculations of ΔH and ΔE where PV work occurs.

    • Hess's Law and characteristics of enthalpy changes.