1.a sample of supercooled water is allowed to form ice at -5degree celsius at 1 atm,it is given that density of water and ice are 0.999 and 0.917 gm per cc, calculate chanfe in gibbs free energy and helmholtZ energy.

vikash kumar, 13 years ago

Grade:

1 Answers

SAGAR SINGH - IIT DELHI

878 Points

13 years ago

Dear student,

The Gibbs Free Energy is a thermodynamic quantity which can be used to determine if a reaction is spontaneous or not. The definition of the Gibbs free energy is

G = H- T*S

where G is the free energy, H is the enthalpy and S is the entropy. If we consider the change in G for a reaction where the temperature does not change, we have

DG = DH - TDS

DH and DS are computed from the usual procedures. Temperatures for this equation must be in Kelvin. The above equation is often known as the "Gibbs-Helmholtz equation". Since the values of DH and DS are usually gotten from tables of standard entropy and enthalpy, the Gibbs free energy change usually computed is the standard Gibbs free energy change, DG⁰ at 25⁰C- for different temps the procedure is similar

The sign of DG determines if a reaction is spontaneous or not.

DG < 0: the reaction is spontaneous
DG > 0: the reaction is not spontaneous
DG = 0: the reaction is at equilivrium

Please feel free to ask your queries here. We are all IITians and here to help you in your IIT JEE preparation.

All the best.

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