Gibbs energy, spontaneity and the equilibrium constant — NEET & JEE Questions

Question 1 · difficulty L1 · recall

At constant temperature and pressure, a process is thermodynamically spontaneous when

• A. $\Delta G<0$
• B. $\Delta G>0$
• C. $\Delta G=+\infty$
• D. $\Delta H=0$ is the only requirement

Question 2 · difficulty L2 · understanding

At equilibrium at constant temperature and pressure, the Gibbs energy change for an infinitesimal net reaction is

• A. zero
• B. always positive
• C. always negative
• D. equal to enthalpy only

Question 3 · difficulty L2 · understanding

The Gibbs energy relation is

• A. $\Delta G=\Delta H-T\Delta S$
• B. $\Delta G=\Delta H+T\Delta S$
• C. $\Delta G=T\Delta H-\Delta S$
• D. $\Delta G=\Delta S-T\Delta H$

Question 4 · difficulty L2 · understanding

For a reaction with $K>1$ under standard-state thermodynamics, $\Delta G^\circ$ is generally

• A. negative
• B. positive
• C. always zero
• D. undefined

Question 5 · difficulty L3 · application

A process has $\Delta H=-40$ kJ mol$^{-1}$ and $\Delta S=+100$ J mol$^{-1}$ K$^{-1}$ at 300 K. What is $\Delta G$?

• A. $-70$ kJ mol$^{-1}$
• B. $-10$ kJ mol$^{-1}$
• C. $+70$ kJ mol$^{-1}$
• D. $+10$ kJ mol$^{-1}$

Question 6 · difficulty L3 · application

A reaction has $\Delta H=+20$ kJ mol$^{-1}$ and $\Delta S=+100$ J mol$^{-1}$ K$^{-1}$. Above what temperature does $\Delta G$ become negative?

• A. 200 K
• B. 100 K
• C. 20 K
• D. 2000 K

Question 7 · difficulty L3 · application

If $\Delta G^\circ=0$ for a reaction at a given temperature, what is the equilibrium constant?

• A. 1
• B. 0
• C. 10
• D. infinite

Question 8 · difficulty L3 · application

At 298 K, if a reaction has a very large equilibrium constant, which statement is most reasonable?

• A. Products are strongly favoured at equilibrium and $\Delta G^\circ$ is negative
• B. Reactants are strongly favoured and $\Delta G^\circ$ is positive
• C. $\Delta G^\circ$ must be zero
• D. K is unrelated to thermodynamics

Question 9 · difficulty L4 · application

A reaction has $\Delta H<0$ and $\Delta S>0$. What can be said about spontaneity?

• A. It is thermodynamically favourable at all temperatures
• B. It is favourable only at high temperature
• C. It is favourable only at low temperature
• D. It is never favourable

Question 10 · difficulty L4 · application

A reaction has $\Delta H>0$ and $\Delta S<0$. What can be said about spontaneity under standard conditions?

• A. It is unfavourable at all temperatures
• B. It is favourable at high temperature
• C. It is favourable at low temperature
• D. It is always at equilibrium