In the reaction H, H+H, there is an average energy change of 436 kJ/mol. This is an
(endothermic/exothermic) reaction
which means that energy is being
(absorbed/released) during the
overall reaction.

Because a model would make the investigation easier to understand

The independent variable is the type of music.the dependent variable is the pulse rate.the intervening variable is the age of the subject.if the mother does not like rock, her pulse is likely to not increase.the same might be true for the sister.the friend may like rap and gets excited.to establish cause/effect relationship, all of the subjects must be consistent.hope i .