ACS Physical Chemistry
Thermochemistry Study Guide
2025/2026 Exam Questions and Correct
Answers | New Update
What is the third law of thermodynamics? - 🧠ANSWER ✔✔The entropy of a
perfect crystal is zero.
What is the second law of thermodynamics? - 🧠ANSWER ✔✔As a whole,
the universe always tends towards increasing entropy.
What is the relationship between number of microstates and entropy? -
🧠ANSWER ✔✔More microstates = higher entropy
What is the relationship between temperature and entropy? - 🧠ANSWER
✔✔Temperature increases, entropy increases (direct)
,What is the relationship between atomic weight and entropy? - 🧠ANSWER
✔✔Heavier = increased entropy (direct)
What happens to entropy when a substance is dissolved in another? -
🧠ANSWER ✔✔Entropy increases
What is the relationship between moles of gas and entropy? - 🧠ANSWER
✔✔When moles of gas increase, entropy increases (direct)
What is the relationship between free energy, enthalpy, and entropy? -
🧠ANSWER ✔✔deltaG(system)=deltaH(system)-TdeltaS(system)
What does change in G measure? - 🧠ANSWER ✔✔The extent of the
spontaneity of a process, and the useful energy available from it
What is the relationship between work and spontaneous processes? -
🧠ANSWER ✔✔Spontaneous processes produce work
What is the relationship between work and non-spontaneous processes? -
🧠ANSWER ✔✔Non-spontaneous processes require work
What does -w mean? - 🧠ANSWER ✔✔Work is being produced -
spontaneous
,What does a positive sign for w mean? - 🧠ANSWER ✔✔Work is required -
non-spontaneous
Can a change be spontaneous in both directions? - 🧠ANSWER ✔✔No
What is an extensive property? - 🧠ANSWER ✔✔Value depends on the
amount of substance
What does ΔG > 0 mean? - 🧠ANSWER ✔✔Non-spontaneous process -
requires work
What does ΔG < 0 mean? - 🧠ANSWER ✔✔Spontaneous process -
produces work
What does standard free energy of formation mean? ΔGo - 🧠ANSWER
✔✔The free energy change that occurs when 1 mole of a compound is
made from its elements
What is the standard free energy of formation for an element in its standard
state? ΔGf - 🧠ANSWER ✔✔0
What does reversing a reaction do to the standard free energy of
formation? ΔG0 - 🧠ANSWER ✔✔Changes its sign
3
COPYRIGHT©JOSHCLAY 2025/2026. YEAR PUBLISHED 2025. COMPANY REGISTRATION NUMBER: 619652435. TERMS OF USE. PRIVACY
STATEMENT. ALL RIGHTS RESERVED
, Why are most exothermic reactions spontaneous? - 🧠ANSWER
✔✔Because the large negative ΔH/large energy release makes the free
energy change negative.
What happens when ΔH and ΔS have opposite signs? - 🧠ANSWER ✔✔The
reaction occurs spontaneously at all temperatures or at none.
What happens when enthalpy (ΔH) is negative and entropy (ΔS) is
positive? - 🧠ANSWER ✔✔Spontaneous at all temperatures, negative free
energy
What is the likely sign of ΔH and ΔS for a combustion reaction? -
🧠ANSWER ✔✔Negative ΔH, positive ΔS
What happens when ΔH is positive and ΔS is negative? - 🧠ANSWER
✔✔Nonspontaneous at all temperatures
What happens when ΔH and ΔS are both positive? - 🧠ANSWER
✔✔Reaction becomes spontaneous as temperature increases
What happens when ΔH and ΔS are both negative? - 🧠ANSWER
✔✔Reaction becomes spontaneous as temperature decreases
Thermochemistry Study Guide
2025/2026 Exam Questions and Correct
Answers | New Update
What is the third law of thermodynamics? - 🧠ANSWER ✔✔The entropy of a
perfect crystal is zero.
What is the second law of thermodynamics? - 🧠ANSWER ✔✔As a whole,
the universe always tends towards increasing entropy.
What is the relationship between number of microstates and entropy? -
🧠ANSWER ✔✔More microstates = higher entropy
What is the relationship between temperature and entropy? - 🧠ANSWER
✔✔Temperature increases, entropy increases (direct)
,What is the relationship between atomic weight and entropy? - 🧠ANSWER
✔✔Heavier = increased entropy (direct)
What happens to entropy when a substance is dissolved in another? -
🧠ANSWER ✔✔Entropy increases
What is the relationship between moles of gas and entropy? - 🧠ANSWER
✔✔When moles of gas increase, entropy increases (direct)
What is the relationship between free energy, enthalpy, and entropy? -
🧠ANSWER ✔✔deltaG(system)=deltaH(system)-TdeltaS(system)
What does change in G measure? - 🧠ANSWER ✔✔The extent of the
spontaneity of a process, and the useful energy available from it
What is the relationship between work and spontaneous processes? -
🧠ANSWER ✔✔Spontaneous processes produce work
What is the relationship between work and non-spontaneous processes? -
🧠ANSWER ✔✔Non-spontaneous processes require work
What does -w mean? - 🧠ANSWER ✔✔Work is being produced -
spontaneous
,What does a positive sign for w mean? - 🧠ANSWER ✔✔Work is required -
non-spontaneous
Can a change be spontaneous in both directions? - 🧠ANSWER ✔✔No
What is an extensive property? - 🧠ANSWER ✔✔Value depends on the
amount of substance
What does ΔG > 0 mean? - 🧠ANSWER ✔✔Non-spontaneous process -
requires work
What does ΔG < 0 mean? - 🧠ANSWER ✔✔Spontaneous process -
produces work
What does standard free energy of formation mean? ΔGo - 🧠ANSWER
✔✔The free energy change that occurs when 1 mole of a compound is
made from its elements
What is the standard free energy of formation for an element in its standard
state? ΔGf - 🧠ANSWER ✔✔0
What does reversing a reaction do to the standard free energy of
formation? ΔG0 - 🧠ANSWER ✔✔Changes its sign
3
COPYRIGHT©JOSHCLAY 2025/2026. YEAR PUBLISHED 2025. COMPANY REGISTRATION NUMBER: 619652435. TERMS OF USE. PRIVACY
STATEMENT. ALL RIGHTS RESERVED
, Why are most exothermic reactions spontaneous? - 🧠ANSWER
✔✔Because the large negative ΔH/large energy release makes the free
energy change negative.
What happens when ΔH and ΔS have opposite signs? - 🧠ANSWER ✔✔The
reaction occurs spontaneously at all temperatures or at none.
What happens when enthalpy (ΔH) is negative and entropy (ΔS) is
positive? - 🧠ANSWER ✔✔Spontaneous at all temperatures, negative free
energy
What is the likely sign of ΔH and ΔS for a combustion reaction? -
🧠ANSWER ✔✔Negative ΔH, positive ΔS
What happens when ΔH is positive and ΔS is negative? - 🧠ANSWER
✔✔Nonspontaneous at all temperatures
What happens when ΔH and ΔS are both positive? - 🧠ANSWER
✔✔Reaction becomes spontaneous as temperature increases
What happens when ΔH and ΔS are both negative? - 🧠ANSWER
✔✔Reaction becomes spontaneous as temperature decreases
