PPT Slide

15

• The enthalpy change during a reaction is called the heat of reaction  or enthalpy of reaction, _Hrxn.

• The sign of _H shows whether heat is absorbed or released.

• Determine its sign by imagining the heat as a ìreactantî or ìproductî.

• When methane burns in air, heat is released, so show it on the right:

• The products (CO 2 and 2H 2O) have less enthalpy than the reactants (CH 4 and 2O 2 ) by the amount of heat released.

Since heat is released, _H (H final ñ H initial ) is negative.

Concept 6-7. The meaning of DH and the distinction between

exothermic and endothermic reactions

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