ACS PHYSICAL CHEMISTRY
THERMOCHEMISTRY STUDY GUIDE
What is the third law of thermodynamics? - Correct Answers -The entropy of a perfect
crystal is zero.
What is the second law of thermodynamics? - Correct Answers -As a whole, the
universe always tends towards increasing entropy.
What is the relationship between number of microstates and entropy? - Correct
Answers -More microstates = higher entropy
What is the relationship between temperature and entropy? - Correct Answers -
Temperature increases, entropy increases (direct)
What is the relationship between atomic weight and entropy? - Correct Answers -
Heavier = increased entropy (direct)
What happens to entropy when a substance is dissolved in another? - Correct Answers
-Entropy increases
What is the relationship between moles of gas and entropy? - Correct Answers -When
moles of gas increase, entropy increases (direct)
What is the relationship between free energy, enthalpy, and entropy? - Correct Answers
-deltaG(system)=deltaH(system)-TdeltaS(system)
What does change in G measure? - Correct Answers -The extent of the spontaneity of a
process, and the useful energy available from it
What is the relationship between work and spontaneous processes? - Correct Answers
-Spontaneous processes produce work
What is the relationship between work and non-spontaneous processes? - Correct
Answers -Non-spontaneous processes require work
What does -w mean? - Correct Answers -Work is being produced - spontaneous
,What does a positive sign for w mean? - Correct Answers -Work is required - non-
spontaneous
Can a change be spontaneous in both directions? - Correct Answers -No
What is an extensive property? - Correct Answers -Value depends on the amount of
substance
What does ΔG > 0 mean? - Correct Answers -Non-spontaneous process - requires work
What does ΔG < 0 mean? - Correct Answers -Spontaneous process - produces work
What does standard free energy of formation mean? ΔGo - Correct Answers -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 -
Correct Answers -0
What does reversing a reaction do to the standard free energy of formation? ΔG0 -
Correct Answers -Changes its sign
Why are most exothermic reactions spontaneous? - Correct Answers -Because the
large negative ΔH/large energy release makes the free energy change negative.
What happens when ΔH and ΔS have opposite signs? - Correct Answers -The reaction
occurs spontaneously at all temperatures or at none.
What happens when enthalpy (ΔH) is negative and entropy (ΔS) is positive? - Correct
Answers -Spontaneous at all temperatures, negative free energy
What is the likely sign of ΔH and ΔS for a combustion reaction? - Correct Answers -
Negative ΔH, positive ΔS
What happens when ΔH is positive and ΔS is negative? - Correct Answers -
Nonspontaneous at all temperatures
What happens when ΔH and ΔS are both positive? - Correct Answers -Reaction
becomes spontaneous as temperature increases
What happens when ΔH and ΔS are both negative? - Correct Answers -Reaction
becomes spontaneous as temperature decreases
Why can the maximum work of a system never obtained from a real process? - Correct
Answers -Because such an irreversible process will always involve some free energy
being converted to heat
, How do you find where a reaction becomes spontaneous? - Correct Answers -Set ΔG
equal to zero and solve -- use T=deltaH/deltaS to find the temperature value.
Is a chemical reaction proceeding to equilibrium a spontaneous or non-spontaneous
change? - Correct Answers -Spontaneous
How to determine reaction direction from ΔG? - Correct Answers -ΔG<0 reaction
proceeds to the right
ΔG>0 reaction proceeds to the left
Which direction does the reaction proceed if ΔG is positive? - Correct Answers -To the
left / to reactants
Which direction does the reaction proceed if ΔG is negative? - Correct Answers -To the
right/ to products
How to predict ΔS(system)? (change in entropy of a system) - Correct Answers -
Positive ΔS(system) means available microstates increases/disorder increases
How to calculate the ΔSo (aka standard entropy change) of the formation of one mole of
gas from its elements? - Correct Answers -1. Write the balanced chemical equation with
the proper coefficients that make the product ONE MOLE.
2. Find the value of the one mole of product in Appendix B. This is the deltaS(standard)
for the product.
3. Find the value of the reactants in Appendix B for deltaS(standard) and multiply them
by the coefficients you got in step 1.
4. Use total = products-reactants for your final value.
How to calculate ΔG (free energy) using enthalpy ΔH and entropy ΔS values? - Correct
Answers -ΔG=ΔH-TΔS
What is the equation that relates ΔG to K? - Correct Answers -ΔG=-RT ln K
What is the Boltzmann constant? - Correct Answers -ln(# of microstates)
What does a big W mean? - Correct Answers -More microstates
What does more microstates mean? - Correct Answers -Big ΔS - more entropy
What does fewer microstates mean? - Correct Answers -Smaller ΔS - less entropy
What happens to entropy when volume is increased? - Correct Answers -Microstates
increase, entropy increases
What is the relationship between ΔS of a system, q, and T? - Correct Answers -
ΔS(system)=qrev/T
THERMOCHEMISTRY STUDY GUIDE
What is the third law of thermodynamics? - Correct Answers -The entropy of a perfect
crystal is zero.
What is the second law of thermodynamics? - Correct Answers -As a whole, the
universe always tends towards increasing entropy.
What is the relationship between number of microstates and entropy? - Correct
Answers -More microstates = higher entropy
What is the relationship between temperature and entropy? - Correct Answers -
Temperature increases, entropy increases (direct)
What is the relationship between atomic weight and entropy? - Correct Answers -
Heavier = increased entropy (direct)
What happens to entropy when a substance is dissolved in another? - Correct Answers
-Entropy increases
What is the relationship between moles of gas and entropy? - Correct Answers -When
moles of gas increase, entropy increases (direct)
What is the relationship between free energy, enthalpy, and entropy? - Correct Answers
-deltaG(system)=deltaH(system)-TdeltaS(system)
What does change in G measure? - Correct Answers -The extent of the spontaneity of a
process, and the useful energy available from it
What is the relationship between work and spontaneous processes? - Correct Answers
-Spontaneous processes produce work
What is the relationship between work and non-spontaneous processes? - Correct
Answers -Non-spontaneous processes require work
What does -w mean? - Correct Answers -Work is being produced - spontaneous
,What does a positive sign for w mean? - Correct Answers -Work is required - non-
spontaneous
Can a change be spontaneous in both directions? - Correct Answers -No
What is an extensive property? - Correct Answers -Value depends on the amount of
substance
What does ΔG > 0 mean? - Correct Answers -Non-spontaneous process - requires work
What does ΔG < 0 mean? - Correct Answers -Spontaneous process - produces work
What does standard free energy of formation mean? ΔGo - Correct Answers -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 -
Correct Answers -0
What does reversing a reaction do to the standard free energy of formation? ΔG0 -
Correct Answers -Changes its sign
Why are most exothermic reactions spontaneous? - Correct Answers -Because the
large negative ΔH/large energy release makes the free energy change negative.
What happens when ΔH and ΔS have opposite signs? - Correct Answers -The reaction
occurs spontaneously at all temperatures or at none.
What happens when enthalpy (ΔH) is negative and entropy (ΔS) is positive? - Correct
Answers -Spontaneous at all temperatures, negative free energy
What is the likely sign of ΔH and ΔS for a combustion reaction? - Correct Answers -
Negative ΔH, positive ΔS
What happens when ΔH is positive and ΔS is negative? - Correct Answers -
Nonspontaneous at all temperatures
What happens when ΔH and ΔS are both positive? - Correct Answers -Reaction
becomes spontaneous as temperature increases
What happens when ΔH and ΔS are both negative? - Correct Answers -Reaction
becomes spontaneous as temperature decreases
Why can the maximum work of a system never obtained from a real process? - Correct
Answers -Because such an irreversible process will always involve some free energy
being converted to heat
, How do you find where a reaction becomes spontaneous? - Correct Answers -Set ΔG
equal to zero and solve -- use T=deltaH/deltaS to find the temperature value.
Is a chemical reaction proceeding to equilibrium a spontaneous or non-spontaneous
change? - Correct Answers -Spontaneous
How to determine reaction direction from ΔG? - Correct Answers -ΔG<0 reaction
proceeds to the right
ΔG>0 reaction proceeds to the left
Which direction does the reaction proceed if ΔG is positive? - Correct Answers -To the
left / to reactants
Which direction does the reaction proceed if ΔG is negative? - Correct Answers -To the
right/ to products
How to predict ΔS(system)? (change in entropy of a system) - Correct Answers -
Positive ΔS(system) means available microstates increases/disorder increases
How to calculate the ΔSo (aka standard entropy change) of the formation of one mole of
gas from its elements? - Correct Answers -1. Write the balanced chemical equation with
the proper coefficients that make the product ONE MOLE.
2. Find the value of the one mole of product in Appendix B. This is the deltaS(standard)
for the product.
3. Find the value of the reactants in Appendix B for deltaS(standard) and multiply them
by the coefficients you got in step 1.
4. Use total = products-reactants for your final value.
How to calculate ΔG (free energy) using enthalpy ΔH and entropy ΔS values? - Correct
Answers -ΔG=ΔH-TΔS
What is the equation that relates ΔG to K? - Correct Answers -ΔG=-RT ln K
What is the Boltzmann constant? - Correct Answers -ln(# of microstates)
What does a big W mean? - Correct Answers -More microstates
What does more microstates mean? - Correct Answers -Big ΔS - more entropy
What does fewer microstates mean? - Correct Answers -Smaller ΔS - less entropy
What happens to entropy when volume is increased? - Correct Answers -Microstates
increase, entropy increases
What is the relationship between ΔS of a system, q, and T? - Correct Answers -
ΔS(system)=qrev/T
