10 points! give an example of a time when introducing an animal into an ecosystem changed it dramatically for the worse

The nile perch.
It was introduced to Lake Victoria in the 1950s and is native to African lake and rivers. 
The population of nile perch exploded in the 1980s, and caused quite a few native species in Lake Victoria to go extinct.

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

Earthquake waves that vibrate from side to side and up and down only through solids are known as "seismic waves."hope my answer has you : )