When does endothermic rwaction becomes spontaneous?
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''Spontaneous reactions are reactions which take place on their own''.
This is true. But, Chemistry defines 'spontaneity' in this way.
''A chemical reaction is spontaneous iff the gibbs free energy associated with it is negative.''
ΔG = ΔH - TΔS :(For spontaneity, ΔG<0)
If this number is negative, then the reaction performs work (Endothermic) otherwise, work is being done on the reaction from an external source (Exothermic). For an endothermic reaction, ΔH is positive. The change in enthalpy of a reaction can be generally understood as the change in heat of a reaction. (If this change is negative, the system gives off heat energy; the reaction is exothermic. If the change in enthalpy is positive, the system absorbs heat energy; the reaction is endothermic).
With ΔH>0, ΔS must be positive and T relatively large for an endothermic reaction to be spontaneous.
Example: Dissolving salt in water.
If you pour table salt into a container of water, the salt dissolves on its own. Enthalpy increases. Entropy increases even more. (Since, you have increased the disorder of the system).The reaction is both endothermic and spontaneous at standard temperature and pressure.
CONCLUSION: If the change in Entropy at a given temperature is sufficient to overcome the unfavorable change in Enthalpy then the reaction will spontaneously occur thus endothermic reactions are possible.
Thanks
This is true. But, Chemistry defines 'spontaneity' in this way.
''A chemical reaction is spontaneous iff the gibbs free energy associated with it is negative.''
ΔG = ΔH - TΔS :(For spontaneity, ΔG<0)
If this number is negative, then the reaction performs work (Endothermic) otherwise, work is being done on the reaction from an external source (Exothermic). For an endothermic reaction, ΔH is positive. The change in enthalpy of a reaction can be generally understood as the change in heat of a reaction. (If this change is negative, the system gives off heat energy; the reaction is exothermic. If the change in enthalpy is positive, the system absorbs heat energy; the reaction is endothermic).
With ΔH>0, ΔS must be positive and T relatively large for an endothermic reaction to be spontaneous.
Example: Dissolving salt in water.
If you pour table salt into a container of water, the salt dissolves on its own. Enthalpy increases. Entropy increases even more. (Since, you have increased the disorder of the system).The reaction is both endothermic and spontaneous at standard temperature and pressure.
CONCLUSION: If the change in Entropy at a given temperature is sufficient to overcome the unfavorable change in Enthalpy then the reaction will spontaneously occur thus endothermic reactions are possible.
Thanks
Answered by
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hola there
''Spontaneous reactions are reactions which take place on their own''.
This is true. But, Chemistry defines 'spontaneity' in this way.
''A chemical reaction is spontaneousiff the gibbs free energy associated with it is negative.''
ΔG = ΔH - TΔS :(For spontaneity, ΔG<0)
''Spontaneous reactions are reactions which take place on their own''.
This is true. But, Chemistry defines 'spontaneity' in this way.
''A chemical reaction is spontaneousiff the gibbs free energy associated with it is negative.''
ΔG = ΔH - TΔS :(For spontaneity, ΔG<0)
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