Where does energy come from? That's a great question! In non-biological scenarios, this energy barrier would be our "activation energy" which would typically be provided by heat or by using an acid or base to change the molecule into a more reactive one! ALL spontaneous and non spontaneous reactions require that one overcomes the ACTIVATION ENERGY barrier. Biologically this is done by ENZYME CATALYSTS, but it does not remove the energy barrier, it reduces it. How? Sometimes the protein catalyst bends the molecule to put strain on it (increasing the energy of the compound) so it is more reactive! Sometimes they bring two substrates so close together that they are FORCED to react. It doesn't matter. There is additional energy necessary to force non-spontaneous reactions to go.