IBChemistryDPHLExam QuestionsWhat Drives Chemical Reactions?Entropy & Spontaneity

Entropy & Spontaneity (DP IB Chemistry: HL): Exam Questions

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Entropy & Spontaneity

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1
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Which change will not decrease the entropy of a system?

  • Changing state from gas to liquid 

  • Decreasing the temperature 

  • A reaction where two moles of gaseous reactants changes to four moles of gaseous products 

  • Reducing the volume of the container for a gaseous reaction

Choose your answer

2
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When solid ammonium chloride dissolves in distilled water, the temperature of the solution decreases. 

What are the signs of ΔHϴ , ΔSϴ , and ΔGϴ for this spontaneous process? 

 

ΔHϴ

ΔSϴ

ΔGϴ

A

-

-

-

B

+

+

+

C

+

+

-

D

+

-

+

    Choose your answer

    3
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    A reaction has a standard entropy change, ΔSΘ of +10.00 J K-1 mol-1. The same reaction has a standard enthalpy change, ΔHΘ, of +10.00 kJ mol-1.

    Calculate the value of ΔGΘ for the reaction in kJ mol-1 at standard temperature. 

    • 9.702

    • 7.02

    • -2970

    • -2980

    Choose your answer

    41 mark

    Propane is produced by the hydrogenation of propene. 

    Formula

    S Θ / J K-1 mol-1

    H2 (g)

    +131

    C3H6 (g)

    +267

    C3H8 (g)

    +270

    Which of the following is the correct entropy change, ΔS Θ, for the reaction?

    • 128

    • 668

    • -668

    • -128

    Choose your answer

    5
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    Which species are arranged in order of decreasing entropy? 

    • C2H6 (g)  >  C2H5OH (l)  > Hg (l)  >  Mg (s)

    • C2H5OH (l)  >  C2H6 (g)  >  Hg (l)  >  Mg (s)

    • Mg (s)  >  C2H5OH (l)  >  Hg (l)  >  C2H6 (g)

    • Mg (s)  >  Hg (l)   >  C2H6 (g)  >  C2H5OH (l) 

    Choose your answer

    11 mark

    Which of the following conditions will mean a reaction is never spontaneous?

     

    ΔH

    ΔS  

    Temperature

    A

    Negative

    Positive

    High

    B

    Positive

    Negative

    High

    C

    Negative

    Negative

    Low

    D

    Positive

    Positive

    High

      Choose your answer

      21 mark

      Ethene is produced according to the following gas-phase synthesis:

      2C (s)  + 2H2 (g) → C2H4 (g) 

      The following thermodynamic data are for this reaction:

      Change

      Value

      ΔHϴr / kJ mol-1

      p

      ΔSϴ / J K-1 mol-1

      q

      The free energy change for this reaction at 298 K is:

      • ΔGϴ = p - 298 x q

      • ΔGϴ = begin mathsize 14px style fraction numerator straight p over denominator 298 cross times begin display style straight q over 1000 end style end fraction end style

      • ΔGϴ = p - 298 x begin mathsize 14px style straight q over 1000 end style

      • ΔGϴ = begin mathsize 14px style fraction numerator straight p cross times 298 over denominator straight q end fraction end style

      Choose your answer

      31 mark

      Which statements are correct for the following reaction?

      CO(NH2)2 (aq) + H2O (l) → CO2 (g) + 2NH3 (g)

      ΔHϴr = +119 kJ mol-1

      ΔSϴ = +354.8 J K-1 mol-1

      I.  The reaction will be spontaneous at high temperatures 

      II.  The reaction will never be spontaneous  

      III.  The reaction becomes more disordered

      • I and II only

      • I and III only

      • II and III only 

      • I, II and III

      Choose your answer

      41 mark

      A reaction becomes spontaneous at temperature T. If ΔHΘ = x kJ mol⁻¹ and ΔSΘ = y J K⁻¹ mol⁻¹, what is the expression for T in Kelvin?

      • T = begin mathsize 14px style x over y end style

      • T = x y

      • T = x + y

      • T = begin mathsize 14px style italic y over italic x end style

      Choose your answer

      51 mark

      The ΔGϴf values for the following substances are shown.

      Substance

      ΔGϴf (kJ mol-1)

      NH3 (g)

      -16.4

      O2 (g)

      0

      H2O (g)

      -228.6

      NO (g)

      87.6

       Which of the following is the correct calculation to determine ΔGϴ? 

      4NH3 (g) + 5O2 (g) ⇌ 6H2O (g) + 4NO (g)

      • -157.4

      • -1087

      • 187.4

      • -955.6

      Choose your answer

      1
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      Which row correctly describes a reaction that only occurs spontaneously at a low temperature?

       

      Reaction

      ΔHreaction

      A

      X (g) + Y (g) → Z (g)

      exothermic

      B

      R (s) →T (g) + U (g) 

      endothermic

      C

      E (g) → 3F (g)

      endothermic

      D

      M (g) + 2N (g) → P (g) + Q (g)

      endothermic

        Choose your answer

        2
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        Urea reacts with water to produce carbon dioxide and ammonia via the following reaction

        CO(NH2)2 (aq) + H2O (l) → CO2 (g) + 2NH3 (g)                    ΔH = 133 kJ mol-1

        Thermodynamic data for the components of this reaction are

        Substance 

        CO(NH2)2 (aq)

        H2O (l)

        CO2 (g)

        NH3 (g)

        Sꝋ (J K-1 mol-1)

        105

        70

        214

        192

        At which of the following temperatures will this reaction become feasible? 

        • 0.3144

        • 3.180

        • 132.6

        • 314.4

        Choose your answer

        3
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        Which reaction occurs with the largest increase in entropy?

        • Pb(NO3)2 (s) + 2KI (s) → PbI2 (s) + 2KNO3 (s) 

        • CaCO3 (s) →  CaO (s) + CO2 (g)

        • 3H2 (g) + N2 (g) →  2NH3 (g)

        • H2 (g) + I2 (g) → 2HI(g)

        Choose your answer

        4
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        Which is correct for the reaction H2O (g) → H2O (l)?

        • Enthalpy increases and entropy increases.

        • Enthalpy decreases and entropy increases.

        • Enthalpy increases and entropy decreases.

        • Enthalpy decreases and entropy decreases.

        Choose your answer

        5
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        Which of the following changes will cause the equilibrium to shift in the direction that increases the system's entropy?

        CaCO3 (s) rightwards harpoon over leftwards harpoon CaO (s) + CO2 (g) ΔHᶿ > 0

        I. Increasing the temperature.

        II. Removing some CO2 (g) from the container.

        III. Decreasing the volume of the container.

        • I and II only

        • I and III only

        • II and III only

        • I, II and III

        Choose your answer