# Calculate the molar heat of solution

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#1
Ok, I've been thinking about this for a while now and I don't know how to answer it. the question goes as follows:

> Calculate the molar heat of solution of calcium chloride in water, knowing that the change in heat content produced from dissolving 1.1gm of this salt equals -0.8 kJ.

I don't know how [(delta)H = H(products) - H(Reactants) = -0.8kJ] ties to [q= mc*(delta)T]
plz help. thx.
0
8 months ago
#2
(Original post by Sentoss)
Ok, I've been thinking about this for a while now and I don't know how to answer it. the question goes as follows:

> Calculate the molar heat of solution of calcium chloride in water, knowing that the change in heat content produced from dissolving 1.1gm of this salt equals -0.8 kJ.

I don't know how [(delta)H = H(products) - H(Reactants) = -0.8kJ] ties to [q= mc*(delta)T]
plz help. thx.
With the data given, you don't need to tie the two relationships together to find the the molar heat of solution

△Hsolution = The enthalpy change when 1 mole of a solute dissolves in excess solvent to make an infinitely dilute solution.

For the dissolution of CaCl2 in water, the reaction is:

CaCl2 (solid) + aq ----------------------> CaCl2 (aq)

Now the data says that 1.11 grams of CaCl2 releases -0.8 kJ.
1.11 grams of CaCl2 = 0.01 moles of CaCl2

So 0.01 moles release -0.8kJ, then 1 mole of CaCl2 (by simple unitary method) will release -80kJ of energy = your answer
0
8 months ago
#3
However, you should know that the two relationships are in fact tied.
ΔH = Energy change
When you write the formula Q = mcΔT, the Q in the equation actually means the heat energy (in Joules). So essentially, Q = ΔH

However, bear in mind that the units for Q are usually in Joules, whereas ΔH is usually quoted in kJ. It is thus important to multiply ΔH by 1000 for both the values to be equal.

So if you find ΔH(in kJ), you then must multiply it by x1000 so that you get the enthalpy change ΔH in Joules, and then you can use the relationship Q = mcΔT by replacing Q with your value of ΔH in Joules
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#4
OH! WOW!!!!!!!!! that's mind blowing!!!!!!! thank you for that.
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