Nemneet Dhather Chemistry 4th Period

Additivity of Heats of Reaction: Hess’s Law
Introduction
In this experiment, we will learn how to use a Styrofoam-cup colorimeter to measure the heat released by three reactions. To do this experiment we need to know about heat which is energy that is being moved because of temperature change between two things. Enthalpy which is a special energy function to make the process of finding how much energy is released or absorbed by a given reaction. Enthalpy is presented by Δ H or Q. Δ represents “a change in” and H represents” heat”. Q represents energy required. To know the reactions presented we must know what the meanings of, exothermic which means releasing heat and endothermic which means to absorb heat. The equation to enthalpy is Q = S x M x Δ T. The Q represents energy required. S represents specific heat capacity. M represents mass of sample in grams and Δ T represents a change in temperature in Celsius degrees. To measure energy we have to know what to measure it by and that is by the joule (calorie). Joule (used to describe heat) is from an SI unit that represents calorie, the amount of energy necessary to increase the temperature of one gram of water by one Celsius degree, which is equal to 4.184 joules. One of the most important features of enthalpy is that it is a state function. This is where Hess’s law principle comes in to play which says, whether the reaction takes place in one step or series of steps the change in enthalpy will always remain the same. Hess’s law helps us calculate heats of reaction that might be difficult to measure directly in a calorimeter. Are the heats of reaction additive? In other words, is the heat or reaction, q, of one reaction equal to the sum of the heats of reaction for the other two reactions? My hypothesis is that I don’t think the heats of all the reactants would be