ACS PHYSICAL CHEMISTRY
THERMOCHEMISTRY EXAM SCRIPT 2026 FULLY
WORKED RESOLUTION
◉ 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
◉ 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
◉ Why can the maximum work of a system never obtained from a
real process? Answer: Because such an irreversible process will
always involve some free energy being converted to heat
◉ How do you find where a reaction becomes spontaneous? Answer:
Set ΔG equal to zero and solve -- use T=deltaH/deltaS to find the
temperature value.
THERMOCHEMISTRY EXAM SCRIPT 2026 FULLY
WORKED RESOLUTION
◉ 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
◉ 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
◉ Why can the maximum work of a system never obtained from a
real process? Answer: Because such an irreversible process will
always involve some free energy being converted to heat
◉ How do you find where a reaction becomes spontaneous? Answer:
Set ΔG equal to zero and solve -- use T=deltaH/deltaS to find the
temperature value.
