( ( For ( an ( exothermic reaction ) ) ) ( ( ( ( ( ( ( the change ) ( in enthalpy ) ) , ) H ) , ) ( as ( we ( ( go ( from ( reactants ( -LRB- ( ( ( methane and ) oxygen ) -RRB- ) ) ) ) ) ( to ( products ( -LRB- ( ( ( ( carbon dioxide ) and ) water ) -RRB- ) ) ) ) ) ) ) ) ( ( is ( a ( negative quantity ) ) ) . ) ) )
(ROOT (S (PP (IN For) (NP (DT an) (JJ exothermic) (NN reaction))) (NP (NP (NP (DT the) (NN change)) (PP (IN in) (NP (NN enthalpy)))) (, ,) (NP (NNP H)) (, ,) (SBAR (IN as) (S (NP (PRP we)) (VP (VBP go) (PP (IN from) (NP (NP (NNS reactants)) (PRN (-LRB- -LRB-) (NP (NP (NN methane)) (CC and) (NP (NN oxygen))) (-RRB- -RRB-)))) (PP (TO to) (NP (NP (NNS products)) (PRN (-LRB- -LRB-) (NP (NP (NN carbon) (NN dioxide)) (CC and) (NP (NN water))) (-RRB- -RRB-)))))))) (VP (VBZ is) (NP (DT a) (JJ negative) (NN quantity))) (. .)))
For an exothermic reaction the change in enthalpy, H , as we go from reactants (methane and oxygen) to products (carbon dioxide and water) is a negative quantity.
(ROOT (S (NP (DT A) (JJ negative) (NN enthalpy) (NN change)) (VP (VBZ is) (VP (VBN observed) (PP (IN in) (NP (DT an) (JJ exothermic) (NN reaction))))) (. .)))