Answer to Question #97596 in General Chemistry for Brittany Wallace

Question

Use the thermochemical data that follow to calculate the value of ΔH° for the reaction:
4 B 2 A + C + 2 F

A + 2B E ΔH° = 70 kJ
C + 2D 2E ΔH° = -25 kJ
F + 2A D ΔH° = 60 kJ

Answer 1

Q97596

Solution:

As Enthalpy $ΔH°$ is an extensive property of a thermodynamic system, it changes with stoichiometric coefficients of the reaction.

Given:

$A + 2B \to E$ $ΔH°_1 = 70 kJ$ ---(1)

$C + 2D \to 2E$ $ΔH°_2 = -25 kJ$ ---(2)

$F + 2A \to D$ $ΔH°_3 = 60 kJ$ ---(3)

To find: $4 B \to 2 A + C + 2 F$ $ΔH°=?$

Now, the required chemical equation can be obtained by doing the following;

$2*(1)-(2)-2*(3)$

Thus, the enthalpy of the required chemical reaction becomes $ΔH°= 2ΔH°_1- ΔH°_2-2 ΔH°_3$

$ΔH°=(2*70)-(-25)-(2*60)$

$=140+25-120$

$=45kJ$