Fill in the coefficients

2HCl - H2 + Cl2

Explanation:

The two hydrochloric acid molecules decompose into one hydrogen molecule (H2) and one chlorine molecule (Cl2). If there is only one type of a specific molecule present, you should not have to add a coefficient of 1 behind it.

answer: enthalpy

explanation:

for a exothermic reaction, the energy is released i.e. the energy of the products is lower than the energy of the reactants.

= enthaply

= energy of products

= energy of reactants

as , thus comes out to be negative. negative value of enthalpy shows that the reaction is exothermic.