( This ( ( means ( that ( ( the ( enthalpy term ) ) ( must ( ( ( be negative ) , ) ( implying ( an ( exothermic reaction ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT This)) (VP (VBZ means) (SBAR (IN that) (S (NP (DT the) (JJ enthalpy) (NN term)) (VP (MD must) (VP (VB be) (ADJP (JJ negative)) (, ,) (S (VP (VBG implying) (NP (DT an) (JJ exothermic) (NN reaction))))))))) (. .)))
This means that the enthalpy term must be negative, implying an exothermic reaction.
(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))))) (. .)))