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the relationship between the enthalpy of a reaction and its classification as endothermic or exothermic

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Pre-lab Questions

1. Define enthalpy.

Enthalpy is a measure of the total energy of a thermodynamic system. It includes the internal energy, which is the energy required to create a system, and the amount of energy required to make room for it by displacing its environment and establishing its volume and pressure. The enthalpy is the preferred expression of system energy changes in many chemical, biological, and physical measurements, because it simplifies certain descriptions of energy transfer. This is because a change in enthalpy takes account of energy transferred to the environment through the expansion of the system under study.

2. What is the relationship between the enthalpy of a reaction and its classification as endothermic or exothermic?

Endothermic reactions draw heat in from their surroundings. Exothermic reactions give heat off to their surroundings.

Endothermic:

· Energy is drawn in from the external environment, causing its surroundings to loose heat, or “cool down.”

· The endothermic chemical reaction creates a product that has a higher energy level than the original materials, causing the reactant’s stored energy to decrease. (In scientific terms, the reactants have “less total enthalpy” than the product.)

· The resulting product of the reaction is less stable because, the higher the energy bond, the less strength its molecules possess.

· Most endothermic reactions are not spontaneous.