Which of the following statements is true? a. some chemical reactions release energy, and other chemical reactions absorb energy. b. chemical reactions, by definition, cannot absorb or release energy. c. some chemical reactions release energy, but no chemical reaction can absorb energy. d. some chemical reactions absorb energy, but no chemical reaction can release energy.

Option (A) is the correct answer.

Explanation:

A reaction that brings changes in chemical composition of a substance is known as a chemical reaction.

When energy is absorbed in a chemical reaction then it is known as an endothermic reaction. Whereas when energy is released in a chemical reaction then it is known as an exothermic reaction.

Therefore, we can conclude that the statement some chemical reactions release energy, and other chemical reactions absorb energy, is true.

answer: enthalpy

explanation:

for a exothermic reaction, the energy is released i.e. the energy of the products is lower than the energy of the reactants.

= enthaply

= energy of products

= energy of reactants

as , thus comes out to be negative. negative value of enthalpy shows that the reaction is exothermic.