When a 7.00-g sample of KCl is dissolved in water in a calorimeter that has a total heat capacity of 5.383 kJ·K–1, the temperature decreases by 0.300 K. Calculate the molar heat of solution of KCl.

Question

photon336 · Answer

I think that this would have to be an endothermic reaction, because energy is absorbed. given by the fact hat the temperature decreases (tf < ti) meaning that heat was absorbed from the surroundings. 

$$7.0g KCl*(\frac{ mol }{ 75.0g }) = 0.09 mol, KCl$$

$$q = mC \delta t $$ 

not sure: 

$$\frac{ 5,383J }{ k (0.09) mol } = 57.9 kj*k ^{-1}mol ^{-1}$$

q = 5.383jk*K^-1

photon336 · Answer

@Cuanchi

photon336 · Answer

@Rushwr C = specific heat, while q = heat capacity right? so all you need to do is put q/moles that's what I thought for this question.

anonymous · Answer

57.9 is wrong.

anonymous · Answer

122 is also wrong.

photon336 · Answer

@Cuanchi @Zale101

photon336 · Answer

had a feeling something was wrong, whoever gets the right answer to this please tag me. I want to see how this is done. @aaronq

anonymous · Answer

Nope, I've tried so many methods and all of them have been wrong so far haha. It should be in kj/mol.

anonymous · Answer

omg. it was as simple at (-.3)(5.383) = 1.61
then divide by (7g/74.5mol) =
17.2

anonymous · Answer

17.2 kj/mol is the answer!

anonymous · Answer

Heat absorbed by calorimeter = (heat capacity of calorimeter)(Tf - Ti)  
then divide by moles to get into the correct units

anonymous · Answer

thanks for all the help!