Thermodynamics: Entropy and Spontaneity
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Questions and Answers

What is the required knowledge to predict spontaneity of a process?

  • Enthalpy only
  • Temperature and Pressure
  • Enthalpy and Entropy (correct)
  • Entropy only

    • What is the sign of ΔH for a fusion of ice into liquid water?

  • Positive (correct)
  • Zero
  • Negative
  • Depends on the temperature

    • What is the relation between entropy and disorder of the system?

  • Greater disorder results in greater entropy (correct)
  • Disorder is a result of lower entropy
  • Entropy is independent of disorder
  • Greater disorder results in lower entropy

    • What is the value of ΔS for a spontaneous reaction?

    <p>Positive</p> Signup and view all the answers

    What is the Third Law of Thermodynamics?

    <p>The entropy of a pure crystalline substance is zero at the absolute zero of temperature</p> Signup and view all the answers

    What is the change in entropy (ΔS) for a reaction?

    <p>ΔS = Sf - Si</p> Signup and view all the answers

    What is the entropy of a pure crystalline substance at 0K?

    <p>Zero</p> Signup and view all the answers

    What is the condition for an equilibrium process?

    <p>ΔSuniv = 0</p> Signup and view all the answers

    What is the sign of ∆H for an exothermic reaction?

    <p>-ve</p> Signup and view all the answers

    Which of the following is an example of a spontaneous process?

    <p>A waterfall running downhill</p> Signup and view all the answers

    What is the characteristic of a spontaneous process in terms of entropy?

    <p>An increase in entropy</p> Signup and view all the answers

    What is the value of ∆H for the combustion of methane?

    <p>-890.4 KJ</p> Signup and view all the answers

    What is the value of ∆H for the acid-base neutralization reaction?

    <p>-56.2 KJ</p> Signup and view all the answers

    What is the characteristic of a non-spontaneous process?

    <p>It requires external assistance to occur</p> Signup and view all the answers

    Is it possible for an endothermic reaction to be spontaneous?

    <p>Yes</p> Signup and view all the answers

    What is the first law of thermodynamics concerned with?

    <p>The total energy remaining the same</p> Signup and view all the answers

    What is the unit of Gibbs free energy?

    <p>J or cal</p> Signup and view all the answers

    What is the sign of ∆G for a spontaneous reaction?

    <p>Negative</p> Signup and view all the answers

    What is the relationship between the standard entropy of gases and liquids?

    <p>The standard entropy of gases is greater than that of liquids</p> Signup and view all the answers

    What is the condition for a reaction to be at equilibrium?

    <p>∆G = 0</p> Signup and view all the answers

    What is the standard free-energy of reaction (∆Gorxn)?

    <p>The free-energy change for a reaction when it occurs under standard-state conditions</p> Signup and view all the answers

    What is the sign of ∆S for a spontaneous process?

    <p>Positive</p> Signup and view all the answers

    What is the condition for a reaction to be non-spontaneous at all temperatures?

    <p>∆H &gt; 0 and ∆S &lt; 0</p> Signup and view all the answers

    What is the absolute zero temperature in Celsius?

    <p>-273.15 °C</p> Signup and view all the answers

    Study Notes

    Thermodynamics

    • The fusion of ice into liquid water is an example of a process with a positive enthalpy change (∆H = 6.01 kJ), but the sign of ∆H alone cannot predict spontaneity.

    Entropy

    • Entropy (S) is a measure of the disorder or randomness of a system.
    • The greater the disorder, the greater the entropy.
    • Solid state has less entropy than liquid state, and liquid state has less entropy than gaseous state.
    • An increase in entropy (∆S > 0) indicates an increase in randomness.
    • Examples of processes with increasing entropy include melting, vaporization, and mixing.

    Entropy Changes in the System

    • The entropy change of the system (∆Ssys) can be positive or negative.
    • For an equilibrium process, ∆Suniv = ∆Ssys + ∆Ssurr = 0.
    • If ∆Suniv is negative, the process is not spontaneous in the direction described.

    Third Law of Thermodynamics

    • The entropy of a pure crystalline substance is zero at absolute zero (0 K).
    • As temperature increases, entropy increases.
    • The standard entropy (S°) of a substance is the entropy at a temperature of 298 K.

    Gibbs Free Energy

    • Gibbs free energy (G) combines enthalpy and entropy to determine spontaneity.
    • The change in free energy (∆G) is given by: ∆G = ∆H - T∆S.
    • ∆G < 0 indicates a spontaneous process, ∆G > 0 indicates a non-spontaneous process, and ∆G = 0 indicates equilibrium.

    Spontaneity and Equilibrium

    • A spontaneous process is characterized by: unidirectional, time-independent, reaches equilibrium, and accompanied by an increase in entropy.
    • Examples of spontaneous processes include a waterfall running downhill, heat flowing from a hotter object to a colder one, and a gas expanding in an evacuated bulb.

    Standard Free-Energy Changes

    • The standard free-energy of reaction (∆Gorxn) is the free-energy change for a reaction under standard-state conditions.
    • ∆H = +ve indicates an endothermic reaction, and ∆H = -ve indicates an exothermic reaction.

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    Understand the role of entropy and enthalpy in determining spontaneity of a process, with a focus on the thermodynamic properties of water.

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