( ( Because ( ( ( the sum ) ( of ( ( the enthalpies ) ( of ( the products ) ) ) ) ) ( is ( smaller ( than ( ( the sum ) ( of ( ( the enthalpies ) ( of ( the reactants ) ) ) ) ) ) ) ) ) ) ( , ( ( exothermic reactions ) ( ( are ( characterized ( by ( ( negative values ) ( of H ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN Because) (S (NP (NP (DT the) (NN sum)) (PP (IN of) (NP (NP (DT the) (NNS enthalpies)) (PP (IN of) (NP (DT the) (NNS products)))))) (VP (VBZ is) (ADJP (ADJP (JJR smaller)) (PP (IN than) (NP (NP (DT the) (NN sum)) (PP (IN of) (NP (NP (DT the) (NNS enthalpies)) (PP (IN of) (NP (DT the) (NNS reactants))))))))))) (, ,) (NP (JJ exothermic) (NNS reactions)) (VP (VBP are) (VP (VBN characterized) (PP (IN by) (NP (NP (JJ negative) (NNS values)) (PP (IN of) (NP (NNP H))))))) (. .)))
Because the sum of the enthalpies of the products is smaller than the sum of the enthalpies of the reactants, exothermic reactions are characterized by negative values of H .
(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))))) (. .)))