Use Hess’s Law to calculate the heat of reaction for the following reaction:

A + 3B → 3C + 2D

A + 2B → C + D H= -20 kJ

B → 2C + D H= -45 kJ

Question 10 options:

+25 kJ

-65 kJ

-25 kJ

+65 kJ

-65kJ

Explanation:

It is possible to calculate the heat of a reaction by the sum of half-reactions, thus:

(a) A + 2B → C + D   ΔH = -20 kJ

(b) B → 2C + D    ΔH = -45 kJ

The sum of (a) + (b) gives:

(a) + (b) A + 3B → 3C + 2D ΔH = -20kJ - 45kJ = -65kJ

Thus, heat of reaction is -65kJ

No

Explanation:

We first find the solubility of the copper sulphate salt

Number of moles= 4.6 moles

Volume =1.75 L

Molarity= number of moles/ volume = 4.6/1.75= 2.6 molL-1

Hence, only 2.6 moles of Copper II sulphate dissolves in 1.75L of water. Hence 4.6 moles of copper II Sulphate dies not dissolve in 1.75 L of water.