When a change occurs spontaneously, it means that once it has begun, it continues without an input of energy.
The two questions are: does the change give off heat energy when it occurs or absorbs heat energy when it occurs, and does the change result in particles becoming more disordered or less disordered?
The relative locations of the reactant energy and product energy indicate whether the overall enthalpy change is endothermic or exothermic.
The energy in an exothermic reaction comes from a source that is supplied to the system in order to start the reaction. For example; water in the magnesium and iron reaction.
Scientists figured out that the net change of the MRE reaction is exothermic, which means it looses energy to its surroundings. Scientists were able to take this data and make the MRE heat faster.
A catalyst speeds up a reaction by providing a lower energy alternative pathway for the reaction to take. This means that more starting materials at a given temperature have enough energy to make it over the barrier, and in turn heat up quicker.
A graph without the catalyst is steeper, meaning it gets to a higher temperature over a longer period of time, while one with a catalyst heats up quicker, but not to as a high of a temperature.