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| 1. |
Explain Hess\'s law of constant heat summation |
| Answer» ess\'s law of constant heat summation: The law states that the change in enthalpy for a reaction is the same whether the reaction takes place in one or a series of steps. The Hess\'s law can also be stated as the enthalpy change for a chemical reaction is the same regardless of the path by which the reaction occurs.For example, consider following two paths for the preparation of methylene chloridePath I :CH4\u200b(g)+2Cl2\u200b(g)→CH2\u200bCl2\u200b(g)+2HCl(g) ΔH10\u200b=−202.3kJPath II :CH4\u200b(g)+Cl2\u200b(g)→CH3\u200bCl(g)+HCl(g)ΔH20\u200b=−98.3kJCH3\u200bCl(g)+Cl2\u200b(g)→CH2\u200bCl2\u200b(g)+HCl(g)ΔH30\u200b=−104.0kJAdding two stepsCH4\u200b(g)+2Cl2\u200b(g)→CH2\u200bCl2\u200b(g)+2HCl(g) ΔH20=−202.3kJThus whether we follow path I or path II, the enthalpy change of the reaction is same.\xa0ΔH10\u200b=ΔH20\u200b+ΔH30\u200b=−202.3kJ | |