Cl2 is a stable diatomic molecule. It can be decomposed to form two Cl atoms as shown below.
Cl2 → 2Cl(9)
Predict the change in enthalpy (AH) of this reaction.
A) AH is (-); endothermic
B) AH is (+); endothermic
C) AH is (-); exothermic
D) AH is (+); exothermic
E) AH = 0; thermoneutral

Option B: ΔH is (+); endothermic

Explanation:

From the reaction Cl2 → 2Cl(g) given, we can see that the number of moles on the left hand side is 1 while on right hand side, it is 2. This means the number of moles are increasing and it means that the randomness of the system has increased. Also, the bonds are being broken down.

Therefore, the reaction is endothermic. In endothermic reactions, ΔH is positive.

Thus, the correct option is option B.

"you start with 15.67 g mgco3-xh2o, when heated and all the water is removed, you are left with 7.58 g mgco3 only.

therefore, you had 15.67 - 7.58 = 8.09g h2o  

moles of each :

7.58g mgco3 = ? moles = 7.58g / 83.4g/mole = 0.09moles  

8 09g h2o = ? moles = 8.09g / 18g/mole = 0.44moles  

molar ratio between the two by dividing both numbers by the smallest number :

0.09 / 0.09 = 1  

0.44 / 0.09 = 4.8  

mgco3-5h2o"