Which statement is true for most chemical reactions?
a. an energy change occurs during the breaking and forming of bonds.
b. the internal energy of the system increases during a reaction.
c. energy is released during the formation of reactants.
d. the enthalpy of the products is higher than the enthalpy of the reactants.

Option (A) is the correct answer.

Explanation:

In a chemical reaction, the bond between atoms may break or reform. As a result, the potential energy of the reaction will change.

The stronger is the bond between atoms, the more energy will release. Therefore, a chemical reaction can be exothermic or endothermic in nature.

Thus, we can conclude that an energy change occurs during the breaking and forming of bonds in chemical reactions.

The correct answer for above statement is:

An energy change occurs during the breaking and forming of bonds.

Explanation:

A chemical reaction is a method that drives to the chemical conversion of one set of chemical substances to another. Chemical reactions are normally described by a chemical change, and they yield one or more products, which normally have properties distinct from the reactants. Reactions often consist of an arrangement of individual sub-steps, the so-called primary reactions, and the information on the specific course of action is part of the reaction tool.

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-

i believe the answer is three water molecules