SolutionsConcept of Chemical Reaction
1. Energy balance
In a reaction, 400 kJ must be supplied to break the bonds of the reactants and 500 kJ are released when those of the products form. Is it favourable? How much energy is released?
Yes: 500 − 400 = 100 kJ are released. It is an exothermic reaction.
2. Favourable but slow
The combustion of methane is very favourable. Why does the gas in a kitchen not burn by itself when it mixes with air?
Because, although the energy balance is favourable, an activation energy must be overcome: a spark or a flame is needed to start the reaction.