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IBChemistryHLExam QuestionsWhat Drives Chemical Reactions?Entropy & Spontaneity

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Entropy & Spontaneity (HL IB Chemistry)

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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

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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. + - +

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    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

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    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

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    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) 

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    11 mark

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

     

    ΔH

    ΔS  

    Temperature

    A

    Negative

    Positive

    High

    B

    Positive

    Negative

    High

    C

    Negative

    Negative

    Low

    D

    Positive

    Positive

    High

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      21 mark

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

      2C (s)  + 2H2 (g) → C2H4 (g) 

      Thermodynamic data for the components of this equilibrium are

      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

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      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

      1.   The reaction will be feasible at high temperatures 
      2.   The reaction will never be feasible 
      3.   The reaction becomes more disordered

      • I and II only

      • I and III only

      • II and III only 

      • I, II and III

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      41 mark

      Which of the following equations is used when calculating the temperature, in Kelvin, at which a reaction becomes feasible if ΔHΘ = x and ΔSΘ = y.

      • 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

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      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

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      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

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        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

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        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)

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        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.

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        5
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        Which factors will increase the entropy of this system?

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

        I.     Increasing the temperature without changing the volume of the container.

        II.     Decreasing the concentration of the gas without changing the volume of the container.

        III.     Increasing the pressure without changing the volume of the container.

        • I and II only

        • I and III only

        • II and III only

        • I, II and III

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