Thermodynamics Chapter Quiz
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Questions and Answers

What is the equation used to calculate the change in Gibbs Free Energy for a spontaneous process?

  • ΔG = ΔH + TΔS
  • ΔG = TΔS - ΔH
  • ΔG = ΔH - TΔS (correct)
  • ΔG = ΔS + TΔH

    • According to the third law of thermodynamics, what is the entropy value of a perfect crystalline substance at absolute zero?

  • Infinite
  • k J K
  • 0 J K (correct)
  • 1 J K

    • At what temperature does the inequality ΔSuniverse > 0 hold for the reaction involving NH4Cl(s) if ΔHrxn is -176.8 kJ/mol and ΔSsys is -285.44 J/K·mol?

  • 200 K
  • 619 K (correct)
  • 285 K
  • 176.8 K

    • What is the change in entropy for the system when converting Br2(l) to Br2(g)?

    <p>92.8 J K–1 mol–1</p> Signup and view all the answers

    Which of the following contributes to the spontaneity of a process according to the second law of thermodynamics?

    <p>The sum of the changes in entropy of the system and surroundings</p> Signup and view all the answers

    What happens during an exothermic reaction?

    <p>Energy is released to the surroundings.</p> Signup and view all the answers

    What does the equation ΔU = q + w represent?

    <p>The heat and work associated with a system.</p> Signup and view all the answers

    Which statement is true regarding standard enthalpy of formation (ΔH°f)?

    <p>ΔH°f refers to heat change from elements in their standard states.</p> Signup and view all the answers

    What is the main criterion for a process to be classified as spontaneous?

    <p>It occurs under specific conditions.</p> Signup and view all the answers

    Which of the following describes a non-spontaneous process?

    <p>A process that does not occur under specific conditions.</p> Signup and view all the answers

    Under constant pressure, how is enthalpy change (ΔH) related to heat (q)?

    <p>ΔH is always equal to q.</p> Signup and view all the answers

    What represents the first law of thermodynamics?

    <p>The total energy of the universe is constant.</p> Signup and view all the answers

    Which condition typically leads to a positive Gibbs free energy (G)?

    <p>The reaction is endothermic.</p> Signup and view all the answers

    What does a large magnitude of $ΔG°$ indicate about the position of equilibrium?

    <p>Equilibrium significantly favors either the reactant or product side.</p> Signup and view all the answers

    What does $ΔG$ represent at any point on a free energy diagram?

    <p>The slope indicating the direction toward equilibrium.</p> Signup and view all the answers

    How can a reaction approach equilibrium according to the free energy diagram?

    <p>From either the reactants or products side.</p> Signup and view all the answers

    Which statement accurately describes the lowest point on a free energy diagram?

    <p>It indicates the position of equilibrium.</p> Signup and view all the answers

    Which of the following contributes to a higher standard entropy S°?

    <p>Diatomic gas molecules</p> Signup and view all the answers

    What is the relationship between free energy changes and temperature?

    <p>Free energy can change with temperature, affecting the reaction.</p> Signup and view all the answers

    What is the relationship between diamond and graphite in terms of standard entropy S°?

    <p>Diamond has lower S° because of its 3D structure</p> Signup and view all the answers

    Which species would most likely have the highest standard entropy S°?

    <p>Carbon dioxide gas</p> Signup and view all the answers

    How does the entropy of an aqueous solution compare to that of a pure solid?

    <p>S°aqueous &gt; S°pure solid</p> Signup and view all the answers

    In which of the following conditions would the entropy of the universe ΔSuniverse decrease?

    <p>An equilibrium process</p> Signup and view all the answers

    What happens to the system's entropy when smaller hydrated ions are present?

    <p>The solute entropy dominates, resulting in S°system &gt; 0</p> Signup and view all the answers

    Which of the following scenarios results in an increase in entropy?

    <p>Liquid nitrogen evaporates</p> Signup and view all the answers

    Which factor does NOT contribute to greater standard entropy S° in a gas?

    <p>Fewer moles of gas</p> Signup and view all the answers

    What is the sign of ΔSsystem when liquid water freezes below 0°C?

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

    How does the surroundings' entropy change when water freezes below 0°C?

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

    What can be inferred about the spontaneity of a reaction with a positive ΔSuniverse?

    <p>It is spontaneous.</p> Signup and view all the answers

    What happens to ΔSsurr if the temperature is above 0°C during an endothermic process?

    <p>It decreases.</p> Signup and view all the answers

    What is the relationship between ΔSsurr and temperature for spontaneous reactions?

    <p>ΔSsurr is inversely proportional to T.</p> Signup and view all the answers

    In the synthesis of ammonia, what was the calculated value for ΔSsys?

    <p>-198.5 J K–1 mol–1</p> Signup and view all the answers

    What is the calculated value of ΔSuniverse for the reaction H2O2(l) → H2O2(g) at 163°C?

    <p>5.3 J K–1 mol–1</p> Signup and view all the answers

    At what condition is the reaction NH3(g) + HCl(g) → NH4Cl(s) no longer spontaneous?

    <p>At high temperatures</p> Signup and view all the answers

    What is the calculated value of the entropy S for Fe(OH)3(s)?

    <p>107.9 J K⁻¹ mol⁻¹</p> Signup and view all the answers

    Which of the following correctly describes standard state conditions for gases?

    <p>1 atm pressure</p> Signup and view all the answers

    What is ΔH for the reaction calculated in the solution?

    <p>-1582.2 kJ</p> Signup and view all the answers

    What value does ΔG°f equal for elements in their standard states?

    <p>0 kJ</p> Signup and view all the answers

    What is the formula used to calculate ΔG° from the reaction components?

    <p>ΔG° = ΔH° - TΔS°</p> Signup and view all the answers

    At what temperature is ΔG being approximately estimated in the given equations?

    <p>298 K</p> Signup and view all the answers

    What unit is used to express entropy, S?

    <p>J/K mol</p> Signup and view all the answers

    Which of the following conditions is required to compute ΔG from ΔG°?

    <p>Knowledge of temperature and reaction direction</p> Signup and view all the answers

    Study Notes

    Thermodynamics and Spontaneous Processes

    • Thermodynamics studies the interconversion of energy forms.
    • A system is the part of the universe of interest, and surroundings are everything else.
    • Exothermic reactions transfer energy from the system to the surroundings.
    • Endothermic reactions transfer energy from the surroundings to the system.
    • The first law of thermodynamics states energy cannot be created or destroyed, only transferred.

    First Law of Thermodynamics

    • ∆U(universe) = 0
    • ∆U(system) = -∆U(surroundings)

    Enthalpy and Enthalpy of Reaction

    • Enthalpy (H) = U + PV
    • Enthalpy of reaction (∆H) = ∆H(products) - ∆H(reactants).
    • ∆H > 0, endothermic reaction.
    • ∆H < 0, exothermic reaction.
    • Standard enthalpies of formation (∆H°f) represent the heat change when one mole of a compound is formed from its elements in their standard states.

    Spontaneous Processes

    • Spontaneous processes occur under specific conditions.
    • Non-spontaneous processes do not occur under specific conditions.
    • Enthalpy(∆H) can predict spontaneity; ∆H < 0 (exothermic) = spontaneous, ∆H > 0 (endothermic) = not spontaneous.

    Entropy

    • Entropy (S) is a measure of how spread out energy is or how dispersed a system's energy.
    • More dispersed energy = increased entropy.
    • Nature tends toward states with higher entropy.
    • ∆S > 0 (increased entropy) = favorable/spontaneous.
    • Entropy is a state function, hence AS = Sfinal - Sinitial.
    • Standard entropy(S°) is the absolute entropy of a substance at 1 atm and typically 25°C.
    • Gas phase entropy > liquid phase entropy > solid phase entropy for the same substance; more complex molecules have higher entropy.
    • S° increases with increasing temperature, more complex molecules, and larger number of particles.
    • Entropy for monatomic species increases with increasing atomic mass

    Gibbs Free Energy

    • Gibbs Free Energy (G) is defined as G = H - TS.
    • ∆G < 0 (Gibbs Free Energy is negative) = spontaneous in the forward direction.
    • ∆G = 0 = system at equilibrium.
    • ∆G > 0 = NOT Spontaneous in the forward direction.
    • ∆G° is the standard free energy change at standard conditions , which is at 298K and 1atm.

    Relationship between ∆G and Equilibrium

    • ∆G° = -RTlnK
    • K= equilibrium constant
    • R= ideal gas constant
    • T= temperature.
    • Q= reaction quotient
    • If Q < K or Q/K < 1 then ∆G < 0.
    • If Q > K or Q/K > 1 then ∆G > 0.
    • If Q = K then ∆G = 0.

    Third Law of Thermodynamics

    • The entropy of a perfect crystalline substance at 0 K is zero

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    Description

    Test your understanding of thermodynamics concepts with this quiz focused on Gibbs Free Energy, entropy, and the laws of thermodynamics. Questions cover spontaneous processes, exothermic reactions, and enthalpy changes. Ideal for students looking to reinforce their knowledge of this critical subject.

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