1 MAXE · 401 MEHC
★ ★
University of Wisconsin–Madison
W Department of Chemistry
EST. 1848
NUMEN LUMEN · THE WISCONSIN IDEA
Chem 104 Exam 1 Study Guide
G E N E RA L C H E M I ST RY I I — T H E R M O DY N A M I CS & S P O N TA N E I TY
INSTITUTION University of Wisconsin–Madison PROGRAM Bachelor of Science — General
Chemistry II
COURSE CODE Chem 104 COURSE TITLE General Chemistry II
ACADEMIC YEAR EXAM TITLE Chem 104 Exam 1 Study Guide
TOTAL QUESTIONS 33 Questions FORMAT Multiple Choice — Select the
Single Best Answer
STUDY GUIDE INSTRUCTIONS
▸ This study guide covers thermodynamics, spontaneity, entropy, free energy, and related calculations for
Chem 104 Exam 1.
▸ Each question tests one discrete concept, definition, or calculation method from the course material.
▸ Select the single best answer for each question. Correct answers and detailed rationales are provided for
self-assessment.
▸ Pay careful attention to sign conventions (positive/negative ΔH, ΔS, ΔG) and their relationship to
spontaneity.
▸ All thermodynamic equations and constants reflect standard General Chemistry II curriculum at UW–
Madison.
, CHEM 104 — THERMODYNAMICS, ENTROPY & FREE
Questions 1 – 33
ENERGY
1. Calculate the standard entropy change (ΔS˚) for the reaction 2C (g) + 2H₂ (g) → C₂H₄ (g)
using the following standard entropies: S˚ C = 5.740 J mol⁻¹ K⁻¹, S˚ H₂ = 130.7 J mol⁻¹ K⁻¹,
S˚ C₂H₄ = 219.3 J mol⁻¹ K⁻¹. Report your answer to 3 significant figures.
A. +53.6 J mol⁻¹ K⁻¹
B. −53.6 J mol⁻¹ K⁻¹
C. +272.9 J mol⁻¹ K⁻¹
D. −165.5 J mol⁻¹ K⁻¹
CORRECT ANSWER B — −53.6 J mol⁻¹ K⁻¹
RATIONALE Using ΔS˚ = ΣvS˚(products) − ΣvS˚(reactants): ΔS˚ = [1(219.3)] − [2(5.740) +
2(130.7)] = 219.3 − (11.48 + 261.4) = 219.3 − 272.88 = −53.6 J mol⁻¹ K⁻¹. The
negative value indicates a decrease in entropy, which makes sense because 4
moles of gaseous reactants (2C + 2H₂) combine to form only 1 mole of gaseous
product (C₂H₄), representing a significant decrease in the number of gas particles
and thus a decrease in disorder.
, 2. A process can go forward and return to its original state without permanent changes to
the system or surroundings. Which of the following best defines this type of process, and
which example is correct?
A. Irreversible process — iron rusting
B. Reversible process — the direction can be changed or reversed; water melting, freezing,
and melting again
C. Spontaneous process — an ice cube melting at room temperature
D. Nonspontaneous process — a ball rolling uphill
CORRECT ANSWER B — Reversible process; water melting, freezing, and melting again
RATIONALE A reversible process can go forward and backward, returning to its original state
without permanent changes. Water melting and freezing is the classic example —
the phase change can be reversed by changing temperature. Iron rusting (Option
A) is irreversible. An ice cube melting (Option C) is spontaneous but not the
definition requested. A ball rolling uphill (Option D) is nonspontaneous.
Reversible reactions are denoted with a double arrow (⇌) and can be controlled
by temperature, pressure, or concentration changes.
★ ★
University of Wisconsin–Madison
W Department of Chemistry
EST. 1848
NUMEN LUMEN · THE WISCONSIN IDEA
Chem 104 Exam 1 Study Guide
G E N E RA L C H E M I ST RY I I — T H E R M O DY N A M I CS & S P O N TA N E I TY
INSTITUTION University of Wisconsin–Madison PROGRAM Bachelor of Science — General
Chemistry II
COURSE CODE Chem 104 COURSE TITLE General Chemistry II
ACADEMIC YEAR EXAM TITLE Chem 104 Exam 1 Study Guide
TOTAL QUESTIONS 33 Questions FORMAT Multiple Choice — Select the
Single Best Answer
STUDY GUIDE INSTRUCTIONS
▸ This study guide covers thermodynamics, spontaneity, entropy, free energy, and related calculations for
Chem 104 Exam 1.
▸ Each question tests one discrete concept, definition, or calculation method from the course material.
▸ Select the single best answer for each question. Correct answers and detailed rationales are provided for
self-assessment.
▸ Pay careful attention to sign conventions (positive/negative ΔH, ΔS, ΔG) and their relationship to
spontaneity.
▸ All thermodynamic equations and constants reflect standard General Chemistry II curriculum at UW–
Madison.
, CHEM 104 — THERMODYNAMICS, ENTROPY & FREE
Questions 1 – 33
ENERGY
1. Calculate the standard entropy change (ΔS˚) for the reaction 2C (g) + 2H₂ (g) → C₂H₄ (g)
using the following standard entropies: S˚ C = 5.740 J mol⁻¹ K⁻¹, S˚ H₂ = 130.7 J mol⁻¹ K⁻¹,
S˚ C₂H₄ = 219.3 J mol⁻¹ K⁻¹. Report your answer to 3 significant figures.
A. +53.6 J mol⁻¹ K⁻¹
B. −53.6 J mol⁻¹ K⁻¹
C. +272.9 J mol⁻¹ K⁻¹
D. −165.5 J mol⁻¹ K⁻¹
CORRECT ANSWER B — −53.6 J mol⁻¹ K⁻¹
RATIONALE Using ΔS˚ = ΣvS˚(products) − ΣvS˚(reactants): ΔS˚ = [1(219.3)] − [2(5.740) +
2(130.7)] = 219.3 − (11.48 + 261.4) = 219.3 − 272.88 = −53.6 J mol⁻¹ K⁻¹. The
negative value indicates a decrease in entropy, which makes sense because 4
moles of gaseous reactants (2C + 2H₂) combine to form only 1 mole of gaseous
product (C₂H₄), representing a significant decrease in the number of gas particles
and thus a decrease in disorder.
, 2. A process can go forward and return to its original state without permanent changes to
the system or surroundings. Which of the following best defines this type of process, and
which example is correct?
A. Irreversible process — iron rusting
B. Reversible process — the direction can be changed or reversed; water melting, freezing,
and melting again
C. Spontaneous process — an ice cube melting at room temperature
D. Nonspontaneous process — a ball rolling uphill
CORRECT ANSWER B — Reversible process; water melting, freezing, and melting again
RATIONALE A reversible process can go forward and backward, returning to its original state
without permanent changes. Water melting and freezing is the classic example —
the phase change can be reversed by changing temperature. Iron rusting (Option
A) is irreversible. An ice cube melting (Option C) is spontaneous but not the
definition requested. A ball rolling uphill (Option D) is nonspontaneous.
Reversible reactions are denoted with a double arrow (⇌) and can be controlled
by temperature, pressure, or concentration changes.
