Mixture of salt with water is an endothermic process then why it takes place????????????

Answer 1

The factor that determines whether or not a process will occur is not the enthalpy change, but rather the change in free energy. These are related by the equation:

deltaG = deltaH - T*deltaS

where deltaG = change in free energy
deltaH = enthalpy change (what we commonly term endothermic or exothermic)
T is the temperature in Kelvin
delta S is the change in entropy (the change in disorder of the system, characterised by the degree of random motion of the molecules)

Now for any process to occur, deltaG must be negative. So, in the case of the dissolving of salt in water:
a) as you point out, the process is endothermic, so deltaH is positive
b) however, the amount of disorder in the system is increasing. First of all, from two pure substances, you are ending up with a mixture, and secondly the salt is going from an ordered rigid crystal lattice, to a solution, where the salt ions move about randomly. So the disorder increases, thus deltaS is positive.

However, since you have MINUS T*deltaS, then since deltaS is positive, the second term in the equation is negative, and if T is large enough, the T*deltaS term will be larger than the deltaH term. Thus overall, the deltaG will be negative, and the process takes place.

Answer 2

Endothermic reactions take place by absorbing energy (usually in the form of heat) from the system. It produces a cooling effect.

Answer 3

When salt dissolves in water the sodium ions separate from the chloride ions producing a state with increased "randomness", i.e. entrophy. Increased entropy is a favored reaction. If the increase in entropy overcomes the decrease in energy (not favored) the reaction will take place.

Answer 4

It is endothermic because it takes energy to break the crystal structure. It takes place because of the positive Gibbs function.

Answer 5

It is due to the electrostatic attraction of the partially positive hydrogen pole of the water molecules and the negative chloride ions, or the partially negative oxygen pole of the water molecule and the positive sodium ions.

This electrostatic attraction is enough to overcome the energy difference.

Answer 6

NaCl, a solid is mixed with another compound, HOH. The mix now makes the solid a solution at STP. Thw water is not a solid so..that "heat" makes the solid dissolve. It would get tricky is HOH were solid because it takes 80 cal/btu to change 1g of ice to 1g of HOH at 32F.

Answer 7

Entropy. A reaction can be energetically disfavored but still occur if it increases the system's entropy (disorder) enough to compensate.

Answer 8

spontaneous processes may be energy driven or entropy driven. this is entropy driven process. increase in entropy favours it.

Answer 9

i dont think its a reaction, its just the dissociation of free ions in water...