Calculate the enthalpy for the reaction D + F = G + H using G + C = A + B deltaH = 277
C + F = A delta H = 303
D = B + H delta H = -158

The enthalpy for the reaction : ΔH = -132

Further explanation

Given

Reaction and the enthalpy

Required

the enthalpy

Solution

Hess Law

Reaction 1 reverse :

A + B = G + C  ΔH = -277

Reactions 2 and 3 remain the same (unchanged)

C + F = A         ΔH = 303

D = B + H         ΔH = -158

Add up all the reactions and remove the same compound from two different sides

D + F = G + H  ΔH = -132

Answerthis solution will not form a precipitateexplanationsolubility equilbrium:         pbf₂(s)  ⇄ pb²⁺(aq) + 2 f⁻(aq)the solubility product expression is    (we exclude solids from the equilibrium expression).now suppose we have the trial ion product q, which we can define as    then, we can interpret  q as the product of the concentration of the ions that we have and ksp as the product of the ion concentrations that are needed to form a saturated solution.if q > ksp, then that implies that there will be a surplus of ions that exceed the amount that is required to form a saturated solution. a precipitate will then form (the precipitate continually  forms until the surplus ions are removed and q is decreased to ksp's value).if q = ksp, the saturated solution that forms is barely saturated and the precipitate will be minimal.if q < ksp, then the ion concentration will not be enough to form a saturated solution (so no precipitate).using our information, we calculate the trial ion product:     since q = 2.7  × 10⁻⁸ < ksp =  4  ×  10⁻⁸, a precipitate will not form.

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