Week 11 Lecture Notes - CHY 121 F24
Chapter 5: Thermochemistry
Suggested End-of-Chapter Problems
Problems to solve: 5.4, 5.17, 5.24, 5.27, 5.32, 5.39, 5.42, 5.44, 5.47, 5.53, 5.57, 5.58, 5.64, 5.66, 5.71, 5.75, 5.80
Workshop Hours
Location: Aubert Hall 252
Schedule:
Monday: 8:30 am – 10:00 am
Thursday: 12:30 pm – 2:00 pm
Page 2: Announcements
Mastering Chemistry Homework #11
Platform: Mastering Chemistry and Pearson e-Text
Due Date: 11:59 pm ET on Sunday 11/17/24
Content Coverage: Week 11 lectures
Progress Check #7
Date: Tuesday November 12, 2024 during recitation
Material Covered: Week 10 lectures
Reminder: Bring a non-graphing/non-programmable calculator
Exam III
Date: Tuesday November 26, 2024 during recitation
Note: Scheduled during Thanksgiving week - plan travel accordingly.
Advice: Review and adjust study habits if previous exam performance was unsatisfactory.
Page 3: Opportunities for Help
Important Reminder: Students must check into each help session using a QR code posted in the room.
Page 4: Constant–Pressure Calorimetry
Overview
Coffee Cup Calorimeter:
No physical boundary between the system (reactants) and surroundings (water, calorimeter, etc.).
Thermometer typically in contact with the surroundings, not the system.
Heat change for the system can be related to the heat change of the surroundings.
Page 5: Constant–Pressure Calorimetry Practice
Problem Statement
Solid Ammonium Nitrate Dissolving:
4.25 g of NH4NO3 dissolves in 60.00 g of water.
Temperature drops from 22.0 °C to 16.9 °C.
Specific Heat Capacity (C): 4.184 J/g•K
Calculation Task
Calculate the enthalpy change (ΔH) for the reaction and determine if it is endothermic or exothermic.
Clicker Question: Calculate ΔH in kJ/mol of NH4NO3.
A. 0.33 kJ/mol
B. 5.9 kJ/mol
C. 0.074 kJ/mol
D. 26 kJ/mol
E. 3.0 kJ/mol
Page 6: Constant–Pressure Calorimetry Practice
Problem Statement
Mixing Solutions:
50.0 mL of 1.0 M HCl with 50.0 mL of 1.0 M NaOH in a coffee cup calorimeter.
Temperature increases from 21.0 °C to 27.5 °C.
Density (d): 1.0 g/mL; Specific Heat Capacity (C): 4.184 J/g•K
Calculation Task
Calculate ΔH in kJ/mol HCl for the reaction.
Page 7: Constant–Pressure Calorimetry Practice
Problem Statement
Calorimeter Contents:
95.7 g of H2O (C = 4.184 J/g•K)
121.0 g block of copper (C = 0.385 J/g•K)
Copper Block Temperature Change:
Initial temperature: 104.2 °C to final temperature: 30.1 °C.
Calculation Tasks
Calculate ΔH for the copper block.
Determine the initial temperature of the water before the copper block was added.
Page 8: Hess’s Law
Overview
Hess’s Law:
ΔH for a reaction does not require experimental determination.
Example Steps:
CH4 (g) + 2 O2 (g) → CO2 (g) + 2 H2O (g) ΔH1 = –802 kJ
2 H2O (g) → 2 H2O (l) ΔH2 = –88 kJ
Final reaction: CH4 (g) + 2 O2 (g) → CO2 (g) + 2 H2O (l)
Total ΔH Calculation: ΔHrxn = ΔH1 + ΔH2 = –890 kJ
Page 9: Hess’s Law Approach
Steps to Solve Hess’s Law Problems
Find each compound in the overall equation from step reactions.
Check:
Is the compound on the correct side?
Is the coefficient correct?
Manipulate step reactions and ΔH values (multiply, divide, reverse reactions) to ensure both questions answered positively.
Start with compounds appearing in fewer reactions and cancel out compounds not part of the overall reaction.
Page 10: Hess’s Law Practice
Problem Statement
Conversion of Carbon Forms:
C(graphite) + O2 (g) → CO2 (g) ΔH1 = –393.5 kJ
C(diamond) + O2 (g) → CO2 (g) ΔH2 = –395.4 kJ
Calculate ΔHrxn for the conversion from graphite to diamond and state if it is endothermic or exothermic.
Page 11: Announcements
Continuing Updates for Students
Mastering Chemistry Homework #11:
Location: Mastering Chemistry and Pearson e-Text
Due date: 11:59 pm ET on Sunday 11/17/24
Progress Check #8:
Date: Tuesday November 19, 2024 during recitation
Exam III Reminder:
Date: Tuesday November 26, 2024 during recitation.
Page 12: Opportunities for Help
Important Note: Students must check into help sessions with a QR code in the room.
Page 13: Hess’s Law Practice
Problem Statement
Overall Reaction:
NO (g) + O (g) → NO2 (g) ΔHrxn = ?
Given:
NO (g) + O3 (g) → NO2 (g) + O2 (g) ΔH1 = –198.9 kJ
O3 (g) → 3/2 O2 (g) ΔH2 = –142.3 kJ
O2 (g) → 2 O (g) ΔH3 = 495.0 kJ
Page 14: Hess’s Law Clicker Question
Problem Statement
Calculate ΔHrxn:
Overall: C (s) + H2O (g) → CO (g) + H2 (g) ΔHrxn = ?
Given:
H2 (g) + ½ O2 (g) → H2O (g) ΔH1 = –241.8 kJ
C (s) + O2 (g) → CO2 (g) ΔH2 = –393.5 kJ
2 CO (g) + O2 (g) → 2 CO2 (g) ΔH3 = –566.0 kJ
Choices:
A. –1443.1 kJ
B. –918.3 kJ
C. 131.3 kJ
D. 262.6 kJ
E. 656.1 kJ
Chapter 6: Electronic Structure of Atoms
Suggested End-of-Chapter Problems
Problems to solve: 6.3, 6.11, 6.16, 6.18, 6.20, 6.25, 6.27, 6.32, 6.36, 6.40, 6.46, 6.55, 6.62, 6.72, 6.75, 6.77
Workshop Hours
Location: Aubert Hall 252
Schedule:
Monday: 8:30 am – 10:00 am
Thursday: 12:30 pm – 2:00 pm
Page 16: The Wave Nature of Light
Electromagnetic Radiation
Definition: Carries energy through space at the speed of light (c).
Known as “radiant energy.”
Exhibits wave-like characteristics: pattern of peaks and troughs repeats at regular intervals.
Page 17: The Wave Nature of Light
Key Terms
Wavelength (λ): Distance between two adjacent peaks (or troughs).
Frequency (ν): Number of complete wavelengths that pass a given point each second.
Clicker Question: Wavelength (λ) and frequency (ν) are:
A. Directly proportional
B. Inversely proportional
Page 18: The Wave Nature of Light
Clicker Questions
Question 1: Given wavelength of yellow light from sodium vapor lamp (589 nm), calculate frequency.
Question 2: An FM radio station broadcasts at 103.4 MHz, calculate wavelength.
Choices for Wavelength:
A. 2.899•10–3 m
B. 0.3449 m
C. 2.899•10^5 m
D. 3.449•10–7 m
E. 2.899 m
Choices for Frequency:
A. 1.96•10–15 s–1
B. 19.6 s–1
C. 5.09•10^14 s–1
D. 5.09•10^5 s–1
E. 1.77•10^2 s–1
Page 19: The Wave Nature of Light
Electromagnetic Spectrum
Definition: Arrangement of electromagnetic radiation in order of increasing wavelength (λ).
Properties of each type of radiation arise from differences in wavelength.