DP IB Chemistry: HL

Topic Questions

IBChemistry: HLDPTopic Questions15. Energetics/Thermochemistry (HL only)15.2 Entropy & Spontaneity

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First teaching 2014

Last exams 2024

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15.2 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.

Which of the following is used to calculate the value of ΔGΘ for the reaction in kJ mol-1?

  • 10 - (298 x 0.001) 

  • 10 - (298 x 0.01) 

  • 10 - (298 x 10) 

  • 0.01 - (298 x 10) 

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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 calculation to determine the entropy change, ΔS Θ, for the reaction?

  • (267 +131) - 270

  • 270 + (267 +131) 

  • (-270) - (267 +131) 

  • 270 - (267 + 131) 

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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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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? 

  • fraction numerator 133 over denominator left square bracket 214 plus left parenthesis 2 cross times 192 right parenthesis right square bracket minus left parenthesis 105 plus 70 right parenthesis end fraction

  • fraction numerator left square bracket 214 plus left parenthesis 2 cross times 192 right parenthesis right square bracket minus left parenthesis 105 plus 70 right parenthesis over denominator 133 end fraction

  • 133 minus fraction numerator left square bracket 214 plus left parenthesis 2 cross times 192 right parenthesis right square bracket minus left parenthesis 105 plus 70 right parenthesis over denominator 1000 end fraction

  • fraction numerator 133 cross times 1000 over denominator left square bracket 214 plus left parenthesis 2 cross times 192 right parenthesis right square bracket minus left parenthesis 105 plus 70 right parenthesis end fraction

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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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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)

  • (-228.6 + 87.6) + (-16.4)

  • (-16.4 x 4) - [(-228.6 x 6) + (87.6 x 4)]

  • [-228.6 + (87.6 x 4)] - (-16.4 x 4)

  • [(-228.6 x 6) + (87.6 x 4)] - (-16.4 x 4)

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