ACS Physical Chemistry
Thermochemistry Study
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What is the third law of thermodynamics? -CORRECT ANSWER The entropy of a
perfect crystal is zero.
What is the second law of thermodynamics? -CORRECT ANSWER As a whole, the
universe always tends towards increasing entropy.
What is the relationship between number of microstates and entropy? -CORRECT
ANSWER More microstates = higher entropy
What is the relationship between temperature and entropy? -CORRECT ANSWER
Temperature increases, entropy increases (direct)
What is the relationship between atomic weight and entropy? -CORRECT ANSWER
Heavier = increased entropy (direct)
What happens to entropy when a substance is dissolved in another? -CORRECT
ANSWER Entropy increases
What is the relationship between moles of gas and entropy? -CORRECT ANSWER
When moles of gas increase, entropy increases (direct)
What is the relationship between free energy, enthalpy, and entropy? -CORRECT
ANSWER deltaG(system)=deltaH(system)-TdeltaS(system)
What does change in G measure? -CORRECT 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? -CORRECT
ANSWER Spontaneous processes produce work
What is the relationship between work and non-spontaneous processes? -CORRECT
ANSWER Non-spontaneous processes require work
What does -w mean? -CORRECT ANSWER Work is being produced - spontaneous
What does a positive sign for w mean? -CORRECT ANSWER Work is required - non-
spontaneous
,Can a change be spontaneous in both directions? -CORRECT ANSWER No
What is an extensive property? -CORRECT ANSWER Value depends on the amount
of substance
What does ΔG > 0 mean? -CORRECT ANSWER Non-spontaneous process - requires
work
What does ΔG < 0 mean? -CORRECT ANSWER Spontaneous process - produces
work
What does standard free energy of formation mean? ΔGo -CORRECT 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 -
CORRECT ANSWER 0
What does reversing a reaction do to the standard free energy of formation? ΔG0 -
CORRECT ANSWER Changes its sign
Why are most exothermic reactions spontaneous? -CORRECT ANSWER Because the
large negative ΔH/large energy release makes the free energy change negative.
What happens when ΔH and ΔS have opposite signs? -CORRECT ANSWER The
reaction occurs spontaneously at all temperatures or at none.
What happens when enthalpy (ΔH) is negative and entropy (ΔS) is positive? -
CORRECT ANSWER Spontaneous at all temperatures, negative free energy
What is the likely sign of ΔH and ΔS for a combustion reaction? -CORRECT ANSWER
Negative ΔH, positive ΔS
What happens when ΔH is positive and ΔS is negative? -CORRECT ANSWER
Nonspontaneous at all temperatures
What happens when ΔH and ΔS are both positive? -CORRECT ANSWER Reaction
becomes spontaneous as temperature increases
What happens when ΔH and ΔS are both negative? -CORRECT ANSWER Reaction
becomes spontaneous as temperature decreases
Why can the maximum work of a system never obtained from a real process? -
CORRECT 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? -CORRECT ANSWER 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 ANSWER Spontaneous
How to determine reaction direction from ΔG? -CORRECT ANSWER 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 ANSWER To
the left / to reactants
Which direction does the reaction proceed if ΔG is negative? -CORRECT ANSWER To
the right/ to products
How to predict ΔS(system)? (change in entropy of a system) -CORRECT ANSWER
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 ANSWER 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 ANSWER ΔG=ΔH-TΔS
What is the equation that relates ΔG to K? -CORRECT ANSWER ΔG=-RT ln K
What is the Boltzmann constant? -CORRECT ANSWER ln(# of microstates)
What does a big W mean? -CORRECT ANSWER More microstates
What does more microstates mean? -CORRECT ANSWER Big ΔS - more entropy
What does fewer microstates mean? -CORRECT ANSWER Smaller ΔS - less entropy
What happens to entropy when volume is increased? -CORRECT ANSWER
Microstates increase, entropy increases
What is the relationship between ΔS of a system, q, and T? -CORRECT ANSWER
ΔS(system)=qrev/T
Thermochemistry Study
Guide||Latest Exam
Update||Guaranteed Pass
What is the third law of thermodynamics? -CORRECT ANSWER The entropy of a
perfect crystal is zero.
What is the second law of thermodynamics? -CORRECT ANSWER As a whole, the
universe always tends towards increasing entropy.
What is the relationship between number of microstates and entropy? -CORRECT
ANSWER More microstates = higher entropy
What is the relationship between temperature and entropy? -CORRECT ANSWER
Temperature increases, entropy increases (direct)
What is the relationship between atomic weight and entropy? -CORRECT ANSWER
Heavier = increased entropy (direct)
What happens to entropy when a substance is dissolved in another? -CORRECT
ANSWER Entropy increases
What is the relationship between moles of gas and entropy? -CORRECT ANSWER
When moles of gas increase, entropy increases (direct)
What is the relationship between free energy, enthalpy, and entropy? -CORRECT
ANSWER deltaG(system)=deltaH(system)-TdeltaS(system)
What does change in G measure? -CORRECT 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? -CORRECT
ANSWER Spontaneous processes produce work
What is the relationship between work and non-spontaneous processes? -CORRECT
ANSWER Non-spontaneous processes require work
What does -w mean? -CORRECT ANSWER Work is being produced - spontaneous
What does a positive sign for w mean? -CORRECT ANSWER Work is required - non-
spontaneous
,Can a change be spontaneous in both directions? -CORRECT ANSWER No
What is an extensive property? -CORRECT ANSWER Value depends on the amount
of substance
What does ΔG > 0 mean? -CORRECT ANSWER Non-spontaneous process - requires
work
What does ΔG < 0 mean? -CORRECT ANSWER Spontaneous process - produces
work
What does standard free energy of formation mean? ΔGo -CORRECT 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 -
CORRECT ANSWER 0
What does reversing a reaction do to the standard free energy of formation? ΔG0 -
CORRECT ANSWER Changes its sign
Why are most exothermic reactions spontaneous? -CORRECT ANSWER Because the
large negative ΔH/large energy release makes the free energy change negative.
What happens when ΔH and ΔS have opposite signs? -CORRECT ANSWER The
reaction occurs spontaneously at all temperatures or at none.
What happens when enthalpy (ΔH) is negative and entropy (ΔS) is positive? -
CORRECT ANSWER Spontaneous at all temperatures, negative free energy
What is the likely sign of ΔH and ΔS for a combustion reaction? -CORRECT ANSWER
Negative ΔH, positive ΔS
What happens when ΔH is positive and ΔS is negative? -CORRECT ANSWER
Nonspontaneous at all temperatures
What happens when ΔH and ΔS are both positive? -CORRECT ANSWER Reaction
becomes spontaneous as temperature increases
What happens when ΔH and ΔS are both negative? -CORRECT ANSWER Reaction
becomes spontaneous as temperature decreases
Why can the maximum work of a system never obtained from a real process? -
CORRECT 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? -CORRECT ANSWER 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 ANSWER Spontaneous
How to determine reaction direction from ΔG? -CORRECT ANSWER 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 ANSWER To
the left / to reactants
Which direction does the reaction proceed if ΔG is negative? -CORRECT ANSWER To
the right/ to products
How to predict ΔS(system)? (change in entropy of a system) -CORRECT ANSWER
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 ANSWER 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 ANSWER ΔG=ΔH-TΔS
What is the equation that relates ΔG to K? -CORRECT ANSWER ΔG=-RT ln K
What is the Boltzmann constant? -CORRECT ANSWER ln(# of microstates)
What does a big W mean? -CORRECT ANSWER More microstates
What does more microstates mean? -CORRECT ANSWER Big ΔS - more entropy
What does fewer microstates mean? -CORRECT ANSWER Smaller ΔS - less entropy
What happens to entropy when volume is increased? -CORRECT ANSWER
Microstates increase, entropy increases
What is the relationship between ΔS of a system, q, and T? -CORRECT ANSWER
ΔS(system)=qrev/T
