PPT Slide

39

Formation Reactions and Their Standard Enthalpy Changes

• In a formation reaction, one mole of a compound forms from its  elements.

• The standard heat of formation (_Hƒf ) is the enthalpy change of  the formation reaction with all substances in their standard states.

For the formation of methane (CH 4):

• Table 6.5 shows _Hƒf values for several elements and compounds.

• Note that:

1. An element in its standard state is assigned a _Hƒf of 0.

2. Most compounds have a negative _Hƒf ; compounds are usually more stable than their component elements.

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