The characteristic temperature at which a pure solid changes to a liquid is its point.

1) according to the law of conservation of mass ,in all chemical reactions total mass is unchanged

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Answerδh > 0explanationc₆h₆  (s)  → c₆h₆ (l)if you are changing it from a solid to a liquid, you are pretty much melting the solid. this requires heat energy. therefore, the reaction is endothermic (takes in energy); the system enthalpy increases as the reaction proceeds: δh > 0.