Question

Which of the following conditions will apply conversion of ice to water?
 $\Delta H$, $\Delta S$, $\Delta G$
A. Negative ,negative, negative at low T
B. Negative, negative, positive at low T
C. Positive, positive, positive at low T
D. Positive, positive, negative at low T

Answer 1

Hint: Gibbs free energy is the energy associated with a chemical reaction that can be used to do work. The free energy of the system is the sum of its enthalpy plus the product of its temperature and the entropy of the system.

Complete step by step solution:
As we know that according to Gibbs Free energy,
$\Delta G = \Delta H - T\Delta S$
Now,
The melting of ice is an endothermic process as ice absorbs heat from the surroundings to convert into water.
So, $\Delta H$ for this reaction will be positive.
The randomness of the system increases as solid (ice) changes into liquid (water).
Therefore, $\Delta S$ for this reaction will also be positive.
Now, at low temperature,
 $\Delta H - T\Delta S$ Is positive. So, $\Delta G$ will also be positive at low T.

Hence, option C is correct.

Note: The rusting of iron is an example of a spontaneous reaction that occurs slowly, little by little over time. If a chemical reaction requires an input of energy rather than releasing energy, then $\Delta G$ for that reaction will be a positive value. In this case, the products have more free energy than the reactants.