Entropy, Free Energy and Spontaneity - Thermodynamics - Life Sciences Previous Year Questions

1

2007 · Life Sciences · Thermodynamics · Entropy, Free Energy and Spontaneity

Life Sciences (XL) 2007

The standard free energy change (ΔG°) for the above reaction at 500 K is (R = 8.314 J K^-1 mol^-1)

A

-0.62 kJ/mol

B

-1.43 kJ/mol

C

0.62 kJ/mol

D

1.43 kJ/mol

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2

2007 · Life Sciences · Thermodynamics · Entropy, Free Energy and Spontaneity

Life Sciences (XL) 2007

If ΔG°' for the reaction is -11.7 kJ/mol and R = 8.314 kJ/mol, the reaction is

A

Endergonic at both 37°C and 25°C

B

Endergonic at 37°C and exergonic at 25°C

C

Exergonic at both 37°C and 25°C

D

Exergonic at 37°C and endergonic at 25°C

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3

2009 · Life Sciences · Thermodynamics · Entropy, Free Energy and Spontaneity

Life Sciences (XL) 2009

The reversible and irreversible entropy changes of a system on going from state '1' to state '2' are \( \Delta S_{12}^{rev} \) and \( \Delta S_{12}^{irrev} \) respectively. The correct relationship between the two entropy changes is

A

\(\Delta S_{12}^{rev} > \Delta S_{12}^{irrev} \)

B

\(\Delta S_{12}^{rev} < \Delta S_{12}^{irrev} \)

C

\(\Delta S_{12}^{rev} = \Delta S_{12}^{irrev} \)

D

\(\Delta S_{12}^{rev} = -\Delta S_{12}^{irrev} \)

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4

2010 · Life Sciences · Thermodynamics · Entropy, Free Energy and Spontaneity

Life Sciences (XL) 2010

For a spontaneous process, the total entropy change (ΔS_system + ΔS_surroundings) is

A

equal to zero

B

greater than zero

C

less than zero for endothermic process

D

less than zero for exothermic process

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5

2012 · Life Sciences · Thermodynamics · Entropy, Free Energy and Spontaneity

Life Sciences (XL) 2012

The actual free energy change of a given biochemical reaction carried out under standard conditions with 1 M initial concentration of each of the reactants and products will be

A

equal to zero

B

equal to standard free energy change for the reaction

C

less than the standard free energy change for the reaction

D

greater than the standard free energy change for the reaction

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6

2014 · Life Sciences · Thermodynamics · Entropy, Free Energy and Spontaneity

Life Sciences (XL) 2014

Consider the following biochemical reaction:
Fructose 6-phosphate + ATP → Fructose 1,6-bisphosphate + ADP
The equilibrium constant under biochemical standard conditions (\(K'_{eq}\)) for the above reaction is 254. The standard free energy change (\(\Delta G'^o\)) for the conversion of fructose 6-phosphate is _____________ kJ/mol.

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7

2014 · Life Sciences · Thermodynamics · Entropy, Free Energy and Spontaneity

Life Sciences (XL) 2014

The concentration of Mg²⁺ ions outside a cell is twice the concentration inside. If the transmembrane potential of the cell is −60 mV (inside negative), the free energy change of transporting Mg²⁺ ions across the membrane against the concentration gradient at 37 °C is ________ kJ/mol.
Faraday constant: 96.5 kJ/V mol

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8

2015 · Life Sciences · Thermodynamics · Entropy, Free Energy and Spontaneity

Life Sciences (XL) 2015

Which one of the following about the standard free energy change (ΔG°') and the equilibrium constant (K_eq) of an exergonic reaction, at pH 7.0, is TRUE?

A

ΔG°' is positive and K_eq is less than one

B

ΔG°' is negative and K_eq is less than one

C

ΔG°' is negative and K_eq is greater than one

D

ΔG°' is positive and K_eq is greater than one

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9

2018 · Life Sciences · Thermodynamics · Entropy, Free Energy and Spontaneity

Life Sciences (XL) 2018

One mole of helium gas in an isolated system undergoes a reversible isothermal expansion at 25 °C from an initial volume of 2.0 liters to a final volume of 10.0 liters. The change in entropy (ΔS) of the surroundings is ______ J K⁻¹ (up to two decimal places). (Given: Gas constant R = 8.314 J K⁻¹ mol⁻¹)

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10

2020 · Life Sciences · Thermodynamics · Entropy, Free Energy and Spontaneity

Life Sciences (XL) 2020

At a given pressure, a substance is heated from 2000 K to 2600 K. If the entropy of the substance is 60 J K⁻¹ mol⁻¹, and is assumed to be constant over the given temperature range, then the change in the chemical potential (in kJ mol⁻¹) of the substance is ______.

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11

2022 · Life Sciences · Thermodynamics · Entropy, Free Energy and Spontaneity

Life Sciences (XL) 2022

The equilibrium constant for isomerization of 1-butene to trans-2-butene at 27 °C is _____ (round off to one decimal place).
Given: Gas constant = 8.314 J K^-1 mol^-1
\( \Delta_f G^\circ \) of 1-butene = +71.39 kJ mol^-1
\( \Delta_f G^\circ \) of trans-2-butene = +63.06 kJ mol^-1

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12

2022 · Life Sciences · Thermodynamics · Entropy, Free Energy and Spontaneity

Life Sciences (XL) 2022

The standard free energy changes for conversion of phosphoenol pyruvate (PEP) to pyruvate, and ATP synthesis are shown below. \[ PEP + H_2O \rightleftharpoons pyruvate + P_i \qquad \Delta G'^o = -61.9 \ kJ \cdot mol^{-1} \] \[ ADP + P_i \rightleftharpoons ATP + H_2O \qquad \Delta G'^o = 30.5 \ kJ \cdot mol^{-1} \] The starting concentrations of PEP, ADP, pyruvate, and ATP are 25, 25, 50, and 50 mM, respectively. The value of universal gas constant (R) is 8.315 J · mol⁻¹ K⁻¹. The actual free energy change in kJ · mol⁻¹ for the reaction \[ PEP + ADP \to pyruvate + ATP \] carried out at 37 °C will be ____ (rounded off to one place of decimal).

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13

2023 · Life Sciences · Thermodynamics · Entropy, Free Energy and Spontaneity

Life Sciences (XL) 2023

Which of the following is/are CORRECT when two single complementary strands of DNA come together to form a double helix at a given temperature?
(ΔS and ΔH are changes in entropy and enthalpy of the process, respectively.)

A

ΔS > 0

B

ΔS < 0

C

ΔH > 0

D

ΔH < 0

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14

2024 · Life Sciences · Thermodynamics · Entropy, Free Energy and Spontaneity

Life Sciences (XL) 2024

Which one of the following is the CORRECT representation of the variation of the Gibbs free energy (G) of a substance with temperature (T) at constant pressure?

A

B

C

D

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15

2024 · Life Sciences · Thermodynamics · Entropy, Free Energy and Spontaneity

Life Sciences (XL) 2024

Given the standard reduction potentials (\(E^\ominus\)) for the half-cell reactions below, the standard Gibbs free energy of the dissolution of silver chloride in water, at 298 K, is __________ J mol⁻¹ (rounded off to nearest integer).
(Given: Faraday constant, \(F\) = 96500 C mol⁻¹; \(1\ J = C \times V\)
AgCl(s) + \(e^-\) → Ag(s) + Cl⁻(aq) ; \(E^\ominus\) = 0.22 V at 298 K
Ag⁺(aq) + \(e^-\) → Ag(s) ; \(E^\ominus\) = 0.80 V at 298 K

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