Heats of Reaction: Summary
Key points from this module:
- Formation reaction: reaction to form a compound from its elements (in form normally present in nature).
- Heats or reaction can be determined at 298 K from tabulated values of heats of formation.
- Heats of reaction depend weakly on temperature for many reactions.
- Heats of formation of elements are zero.
- Heat of combustion: heat of reaction of a substance with O2 to usually yield CO2 and H2O.
- The value of a heat of reaction depends on the phases of reactants and products.
- ΔH > 0 for an endothermic reaction.
- ΔH < 0 for an exothermic reaction.
- Heats of reaction can often be calculated from heats of combustion.
From studying this module, you should now be able to:
- Calculate a heat of reaction at standard conditions from heats of formation.
- Given heat of reaction at 298 K, use temperature-dependent heat capacities to calculate heat of reaction at other temperatures.
- Use Hess’s law to calculate a heat of reaction.
- Use heats of combustion to calculate a heat of reaction.
Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder