( ( knows ( that ( ( ( a transfer ) ( of ( thermal energy ) ) ) ( occurs ( in ( chemical reactions ) ) ) ) ) ) . )
(ROOT (S (VP (VBZ knows) (SBAR (IN that) (S (NP (NP (DT a) (NN transfer)) (PP (IN of) (NP (JJ thermal) (NN energy)))) (VP (VBZ occurs) (PP (IN in) (NP (NN chemical) (NNS reactions))))))) (. .)))
knows that a transfer of thermal energy occurs in chemical reactions.
(ROOT (S (NP (NP (DT The) (NN amount)) (PP (IN of) (NP (NP (NN energy)) (VP (VBN required) (S (VP (TO to) (VP (VB begin) (NP (DT a) (JJ chemical) (NN reaction))))))))) (VP (VBZ is) (VP (VBN known) (PP (IN as) (NP (DT the) (NN activation) (NN energy))))) (. .)))