Chemical Forums

Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: iyc on November 10, 2005, 05:25:37 AM

Title: Determination of enthalpy change of hydration of magnesium sulphate(VI)
Post by: iyc on November 10, 2005, 05:25:37 AM

In determination of enthaply change of hydration of MgSO₄:
MgSO₄(s) + 7H₂O -> MgSO₄^.7H₂O(s)
It is impossible to measure the enthalpy change for this reaction. But, I don't know why?
Is it due to the activation energy of the reaction too high that cannot be overcome under standard conndition?

Besides, when M g of anhydrous magnesium sulphate(VI) were add to V cm³ of water in a beaker and all magnesium sulphate is dissolved, there was a maximum rise in temperature of the solution by T^oC. When calculating the enthalpy evolved by using E=mc (deltaT), what should I substitute for mass? Is mass  equal to the sum of mass of anhydrous magnesium sulphate(VI) and mass of water added?

Thank you.

Title: Re:Determination of enthalpy change of hydration of magnesium sulphate(VI)
Post by: GCT on November 10, 2005, 12:45:08 PM

Quote from: iyc on November 10, 2005, 05:25:37 AM

In determination of enthaply change of hydration of MgSO₄:
MgSO₄(s) + 7H₂O -> MgSO₄^.7H₂O(s)
It is impossible to measure the enthalpy change for this reaction. But, I don't know why?
Is it due to the activation energy of the reaction too high that cannot be overcome under standard conndition?

Besides, when M g of anhydrous magnesium sulphate(VI) were add to V cm³ of water in a beaker and all magnesium sulphate is dissolved, there was a maximum rise in temperature of the solution by T^oC. When calculating the enthalpy evolved by using E=mc (deltaT), what should I substitute for mass? Is mass  equal to the sum of mass of anhydrous magnesium sulphate(VI) and mass of water added?

Thank you.

you probably want to work with that of water

Title: Re:Determination of enthalpy change of hydration of magnesium sulphate(VI)
Post by: mike on November 10, 2005, 07:16:04 PM

I would assume that you have to use Hess' Law to determine the enthalpy of hydration. If you added MgSO₄ to water I think you would just be measuring the enthalpy for:

MgSO₄ ------> Mg²⁺ + SO₄^2-

Were you given any equations with corresponding enthalpy changes?

Title: Re:Determination of enthalpy change of hydration of magnesium sulphate(VI)
Post by: iyc on November 10, 2005, 08:38:26 PM

Quote from: iyc on November 10, 2005, 05:25:37 AM

In determination of enthaply change of hydration of MgSO₄:
MgSO₄(s) + 7H₂O -> MgSO₄^.7H₂O(s)
It is impossible to measure the enthalpy change for this reaction directly. But, I don't know why?
Is it due to the activation energy of the reaction too high that cannot be overcome under standard conndition?

In fact, I would like to ask this part.
I think the activation energy of the reaction is too high that cannot be overcome under standard condition. That means, the the reactants are kinetically stable.Is it right if I say so?

Title: Re:Determination of enthalpy change of hydration of magnesium sulphate(VI)
Post by: mike on November 10, 2005, 08:52:04 PM

Well how would you measure it directly?

Title: Re:Determination of enthalpy change of hydration of magnesium sulphate(VI)
Post by: iyc on November 10, 2005, 08:59:30 PM

Can I measure enthalpy change of this reaction MgSO4(s) + 7H2O -> MgSO4.7H2O(s) directly?

If not, is it due to the high activation energy that cannot be overcome spontaneously under standard condition?

Title: Re:Determination of enthalpy change of hydration of magnesium sulphate(VI)
Post by: mike on November 10, 2005, 09:29:11 PM

Quote

MgSO4(s) + 7H2O -> MgSO4.7H2O(s)

I don't think you can measure this directly. Just the practicality of it I think. If you just took MgSO4 and put it in excess water in a calorimeter you would just be measuring the dissociation of MgSO4 I think.

Title: Re:Determination of enthalpy change of hydration of magnesium sulphate(VI)
Post by: iyc on November 11, 2005, 01:31:52 AM

Thank you, I think I can solve the problem.