Measuring the Heat of neutralization!

Introduction

Chemical reactions almost always involve the transfer of heat energy: a reaction will either give off heat, or it will absorb heat. Many times the heat transfer associated with a chemical reaction is more important than the reaction itself. For instance, consider the reaction of methane (CH4, the principal component of natural gas) and oxygen:

CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l)

The water and carbon dioxide produced by this reaction are not nearly as useful as the large amount of heat that it generates. This is heat we can use to heat our homes with a gas furnace, or to heat a reaction beaker with a Bunsen burner.

The study of the heat transfer associated with chemical reactions is called thermochemistry. There are several fundamental terms used in thermochemistry that must be clear to us as we begin this discussion. First, the system is defined as the actual atoms, ions, and molecules that take part in a reaction. Everything else in the universe is part of the surroundings. A reaction which gives off heat is known as an exothermic reaction. More precisely we say that in an exothermic reaction the system gives off heat to the surroundings, resulting in an increase in the temperature of the surroundings. Oppositely, a reaction that absorbs heat is known as an endothermic reaction. In an endothermic reaction the system absorbs heat from the surroundings, causing the temperature of the surroundings to decrease.

exothermic: system gives off heat to surroundings ⇒ Tsurroundings increases
endothermic: system absorbs heat from surroundings ⇒ Tsurroundings decreases

We are often interested in the actual amount of heat transferred in a chemical reaction. By definition, the amount of heat transferred when a reaction is carried out at constant pressure is known as the enthalpy change (ΔH) of the reaction. We often include an "rxn" subscript and refer to ΔHrxn as the enthalpy of reaction, or the heat of reaction. The enthalpy (H) of a substance is related to the total amount of energy the substance
possesses, and the enthalpy change of a reaction is defined as:

ΔHrxn = Hproducts – Hreactants

If ΔHrxn is a negative value, then we can see by Equation 1 that the products possess less enthalpy (energy) than the reactants. Where did this energy go? It was given off by the reaction as heat! In other words, the reaction is exothermic. Therefore, if ΔHrxn is less than zero then the reaction is exothermic. Similarly, if ΔHrxn is greater than zero, the reaction absorbs heat and is endothermic.

ΔHrxn <> 0 ⇒ endothermic

Based on the general information about the neutralization process, I manage to carry out an experiment in the lab using Sodium hydroxide and Hydrochloric acid.