ACS Physical Chemistry
Thermochemistry Study
Guide & Exam Review
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Updated 2026 Questions and Answers
100% Verified Exam Prep and Comprehensive
Rationales
Included
,What is the relationship between atomic weight and Heavier = increased entropy (direct)
entropy?
What happens to entropy when a substance is Entropy increases
dissolved in another?
What is the relationship between moles of gas and When moles of gas increase, entropy increases (direct)
entropy?
What is the relationship between free energy, enthalpy, deltaG(system)=deltaH(system)-TdeltaS(system)
and entropy?
What does change in G measure? The extent of the spontaneity of a process, and the useful energy available
from it
What is the relationship between work and Spontaneous processes produce work
spontaneous processes?
What is the relationship between work and non- Non-spontaneous processes require work
spontaneous processes?
What does -w mean? Work is being produced - spontaneous
What does a positive sign for w mean? Work is required - non-spontaneous
Can a change be spontaneous in both directions? No
What is an extensive property? Value depends on the amount of substance
What does ΔG > 0 mean? Non-spontaneous process - requires work
What does ΔG < 0 mean? Spontaneous process - produces work
What does standard free energy of formation mean? The free energy change that occurs when 1 mole of a compound is made from
ΔGo its elements
What is the standard free energy of formation for an 0
element in its standard state? ΔGf
What does reversing a reaction do to the standard free Changes its sign
energy of formation? ΔG0
Why are most exothermic reactions spontaneous? Because the large negative ΔH/large energy release makes the free energy
change negative.
, What happens when ΔH and ΔS have opposite signs? The reaction occurs spontaneously at all temperatures or at none.
What happens when enthalpy (ΔH) is negative and Spontaneous at all temperatures, negative free energy
entropy (ΔS) is positive?
What is the likely sign of ΔH and ΔS for a combustion Negative ΔH, positive ΔS
reaction?
What happens when ΔH is positive and ΔS is negative? Nonspontaneous at all temperatures
What happens when ΔH and ΔS are both positive? Reaction becomes spontaneous as temperature increases
What happens when ΔH and ΔS are both negative? Reaction becomes spontaneous as temperature decreases
Why can the maximum work of a system never obtained Because such an irreversible process will always involve some free energy
from a real process? being converted to heat
How do you find where a reaction becomes Set ΔG equal to zero and solve -- use T=deltaH/deltaS to find the temperature
spontaneous? value.
Is a chemical reaction proceeding to equilibrium a Spontaneous
spontaneous or non-spontaneous change?
How to determine reaction direction from ΔG? ΔG<0 reaction proceeds to the right
ΔG>0 reaction proceeds to the left
Which direction does the reaction proceed if ΔG is To the left / to reactants
positive?
Which direction does the reaction proceed if ΔG is To the right/ to products
negative?
How to predict ΔS(system)? (change in entropy of a Positive ΔS(system) means available microstates increases/disorder increases
system)
Thermochemistry Study
Guide & Exam Review
| Guaranteed success|
Updated 2026 Questions and Answers
100% Verified Exam Prep and Comprehensive
Rationales
Included
,What is the relationship between atomic weight and Heavier = increased entropy (direct)
entropy?
What happens to entropy when a substance is Entropy increases
dissolved in another?
What is the relationship between moles of gas and When moles of gas increase, entropy increases (direct)
entropy?
What is the relationship between free energy, enthalpy, deltaG(system)=deltaH(system)-TdeltaS(system)
and entropy?
What does change in G measure? The extent of the spontaneity of a process, and the useful energy available
from it
What is the relationship between work and Spontaneous processes produce work
spontaneous processes?
What is the relationship between work and non- Non-spontaneous processes require work
spontaneous processes?
What does -w mean? Work is being produced - spontaneous
What does a positive sign for w mean? Work is required - non-spontaneous
Can a change be spontaneous in both directions? No
What is an extensive property? Value depends on the amount of substance
What does ΔG > 0 mean? Non-spontaneous process - requires work
What does ΔG < 0 mean? Spontaneous process - produces work
What does standard free energy of formation mean? The free energy change that occurs when 1 mole of a compound is made from
ΔGo its elements
What is the standard free energy of formation for an 0
element in its standard state? ΔGf
What does reversing a reaction do to the standard free Changes its sign
energy of formation? ΔG0
Why are most exothermic reactions spontaneous? Because the large negative ΔH/large energy release makes the free energy
change negative.
, What happens when ΔH and ΔS have opposite signs? The reaction occurs spontaneously at all temperatures or at none.
What happens when enthalpy (ΔH) is negative and Spontaneous at all temperatures, negative free energy
entropy (ΔS) is positive?
What is the likely sign of ΔH and ΔS for a combustion Negative ΔH, positive ΔS
reaction?
What happens when ΔH is positive and ΔS is negative? Nonspontaneous at all temperatures
What happens when ΔH and ΔS are both positive? Reaction becomes spontaneous as temperature increases
What happens when ΔH and ΔS are both negative? Reaction becomes spontaneous as temperature decreases
Why can the maximum work of a system never obtained Because such an irreversible process will always involve some free energy
from a real process? being converted to heat
How do you find where a reaction becomes Set ΔG equal to zero and solve -- use T=deltaH/deltaS to find the temperature
spontaneous? value.
Is a chemical reaction proceeding to equilibrium a Spontaneous
spontaneous or non-spontaneous change?
How to determine reaction direction from ΔG? ΔG<0 reaction proceeds to the right
ΔG>0 reaction proceeds to the left
Which direction does the reaction proceed if ΔG is To the left / to reactants
positive?
Which direction does the reaction proceed if ΔG is To the right/ to products
negative?
How to predict ΔS(system)? (change in entropy of a Positive ΔS(system) means available microstates increases/disorder increases
system)
