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    explain the significance of the sign of the value of this enthalpy change.
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    negative sign means that the enthalpy change for the reaction is exothermic so energy is released in the form of heat (lost to the surroundings).

    A positive sign means that the enthalpy change for the reaction is endothermic so energy is required to break the bonds (energy taken in from surroundings).

    Exothermic reactions occur when you form bonds as energy is given out when the bonds are formed.

    Endothermic reactions occur when you break bonds as energy is required to break the bonds.

    Hope this helps
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    The sign of the enthalpy change for a reaction tels you whether the reaction has gained or lost heat energy. If the value is positive then more heat energy has been added to the system - so its endothermic. If the value is negative then heat energy has been given out - exothermic

    edit: beaten :p:
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Updated: November 13, 2008

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