Question

Heat is given off when hydrogen burns in air according to the equation 2H2 + O2->2H2O Which of the following is responsible for the heat? Thats 2 water molecules at the end of the equation

These are the potential answers:
a) Breaking hydrogen bonds gives off energy.
b) Breaking oxygen bonds gives off energy.
c) Forming hydrogen-oxygen bonds gives off energy.
d) Both (a) and (b) are responsible.
e) (a), (b), and (c) are responsible.

Answer 1

Answer:

c) Forming hydrogen-oxygen bonds gives off energy.

Explanation:

a and b cannot be the answers because bond breaking is an endothermic process, it takes in energy. It is bond forming that gives out energy. It is worth noting that even exothermic reactions like this one do take in energy to break the bonds of the reactants first. It is just that the energy they take in is less than the energy they give out during bond formation and that is why the net result is that they are exothermic.