Chemistry Practice Problems Hess's Law Practice Problems Solution: Given the following thermochemical data:          ...

# Solution: Given the following thermochemical data:                                                                                ∆H°f (kJ)I. P4(s) + 6 Cl2(g) ⟶ 4 PCl3(g)                        –1225.6II. P4(s) + 5 O2(g) ⟶ P4O10(s)                         –2967.3III. PCl3(g) + Cl2(g) ⟶ PCl5(g)                         –84.2IV. PCl3(g) + 1/2 O2(g) ⟶ POCl3(g)                –285.7Calculate the value of ∆H° for the following reaction:P4O10(s) + 6 PCl5(g) ⟶ 10 POCl3(g)A. –110.5 kJ B. –610.1 kJ C. –2682.2 kJ D. –4562.8 kJE. –7555.0 kJ

###### Problem

Given the following thermochemical data:

∆H°f (kJ)

I. P4(s) + 6 Cl2(g) ⟶ 4 PCl3(g)                        –1225.6

II. P4(s) + 5 O2(g) ⟶ P4O10(s)                         –2967.3

III. PCl3(g) + Cl2(g) ⟶ PCl5(g)                         –84.2

IV. PCl3(g) + 1/2 O2(g) ⟶ POCl3(g)                –285.7

Calculate the value of ∆H° for the following reaction:

P4O10(s) + 6 PCl5(g) ⟶ 10 POCl3(g)

A. –110.5 kJ

B. –610.1 kJ

C. –2682.2 kJ

D. –4562.8 kJ

E. –7555.0 kJ

###### Solution

We’re being asked to determine the enthalpy change (ΔHrxn) for the chemical reaction:

P4O10(s) + 6 PCl5(g) ⟶ 10 POCl3(g)

We can use Hess’s Law to determine the enthalpy change of the overall reaction from the given reactions:

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