What causes the earths core to be a solid

The high temperature and pressure

Inner core ? the immense pressure from other parts of the planet keep the extremely hot iron of the earths inner core from melting

So  if  the sum of the enthalpies of the reactants is greater than the products, the  reaction  will be  exothermic.  if  the products side has a larger enthalpy, the  reaction  is  endothermic. you may wonder why  endothermic reactions, which soak up energy or enthalpy from the environment, even happen

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