6.5 Enthalpy of Formation
Table of Contents
Add a header to begin generating the table of contents
Standard Enthalpy of Formation
ΔH°rxn = ∑nΔH°products - ∑mΔH°reactants
n = moles products m = moles reactants
Given the following standard enthalpy of formation values, calculate the ΔH°rxn of the following reaction:
3NO(g) → N2O(g) + NO2(g) ΔH°rxn = ?
| ΔHf° (kJ/mol) | |
|---|---|
| NO(g) | 90.4kJ |
| N2O(g) | 81.6kJ |
| NO2(g) | 33.8kJ |
Given the following standard enthalpy of formation values, calculate the ΔH°rxn of the following reaction:
N2H4(g) + O2(g) → N2(g) + 2H2O(g) ΔH°rxn = ?
| ΔHf° (kJ/mol) | |
|---|---|
| N2H4(g) | +95.4kJ |
| H2O(g) | -242kJ |
Formation Reactions
| FORMATION REACTIONS |
|---|
| 1. Form 1 mole of a single product |
| 2. Reactants are elements in their standard state. |
| STANDARD STATES | |
|---|---|
| Gases | He, Ne, Ar, Kr, Xe, Rn, H2, N2, O2, F2, Cl2 |
| Liquids | Br2, Hg |
| Solids | Everything Else |
| Special | C(s, graphite), S8 |
Allotrope – one of multiple possible physical forms of an element
Which of the following are formation reactions?
2H2(g) + O2(g) → 2H2O(l)
CO(g) + ½O2(g) → CO2(g)
C(s, diamond) + O2(g) → CO2(g)
C(s, graphite) + O2(g) → CO2(g)