Why is it difficult to grow crops in northern mexico?
a. because it is too densely populated with trees.
b. because it receives too much rain.
c. because temperatures in the north do not vary much.
d. because the northern parts of mexico are very dry.

D. Because the northern parts of Mexico are very dry.

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