Question

What is the Enthalpy change?
A.The amount of energy as heat that is lost or made by a system.
B.The total amount of energy in a system.
C.A chemical reaction.
D.When energy is neither created nor destroyed.
E.When one or more substances are changed into one or more different substances.

Answer 1

Hint: We know that the enthalpy change in the chemical reactions is due to the bond breaking and making process that occurs in order to lead to the formation of some new products from the pre-existing reactants taken at the start of the reaction. Bond breaking process always requires some energy (in the form of activation energy).

Complete answer:
The total enthalpy change during a chemical reaction is molecularly equal to the amount of heat energy that went into the system from the surroundings or went into the surroundings from the system. In totality, the first law of thermodynamics holds true during every reaction that no amount of heat is either created or destroyed during any reaction. In general, all spontaneous processes or reactions that occur in nature tend to shift their equilibrium towards that side of the reaction where the total enthalpy of the system is decreased i.e., the net amount of energy is lost from the system into the surroundings.
The enthalpy change in the reaction is an important determinant of whether the reaction that is taking place would be an endothermic reaction or an exothermic one. A chemical reaction becomes endothermic when the bonds of the reactant substances which need to be broken for the initiation of the reaction are very strong and require more energy than what is eventually evolved during the formation of new bonds in the product molecules.The Enthalpy change is the amount of heat evolved or absorbed in a reaction carried out at constant pressure.
Therefore, the correct answer is option A.

Note:
Remember that the enthalpy of a reaction is called the standard enthalpy if all the reactants and products are in their standard state. Hence, the overall energy which is required to either break a bond or make a bond, also known as the bond energy, is a very crucial factor which helps in determining the overall change in enthalpy of a particular reaction.