Answer:
Because the enthalpy change of the reaction depends on the states of matter of the substances, they must be shown for each substance in the equation.
Explanation:
The enthalpy of a substance depends on the particular state of matter in which it occurs.
Therefore, in a thermo chemical equation, all the states of matters for all the chemical species in the equation must be accurately written so that the thermo chemical equation can be meaningful.
The answer is A, when these particles are heated they tend to speed up.
A I believe should be right!