Calorimetry Lab Report

The purpose of the lab is to understand how to calculate the calorimeter constant by using a calorimeter. This allows us to analyze the heat reaction of different substances. Calorimetry is a word that comes from both Latin and Greek. The prefix “Calor” in Latin signifies heat and the suffix “metry” in Greek means measuring. Therefore the word itself translates to measuring heat. Joseph Black, was the first scientist to recognize the difference between heat and temperature. Energy is always present in chemical and physical changes. The change of energy that occurs when there is a chemical change at constant pressure is called enthalpy. Enthalpy changes , as well as physical and chemical changes, can be measured by a calorimeter. The energy that is released or absorbed by the reaction can be either absorbed or released by the insulating walls of the instrument.

(eq. 1)

At the beginning of the experiment the heat capacity of the calorimeter is measured. The heat capacity of the instrument is the amount of heat that it absorbs. As energy is released the value is negative and when it is absorbed

the value is positive. In the lab, styrofoam cups acts as calorimeters due to their insulating properties. Since most of the heat that forms is absorbed by the solvent and by the calorimeter, the temperature of the experiment can be altered. The constant of the calorimeter is found by adding scalding water to a known amount of colored water and recording the change in temperature. The amount of heat the hot water released should be equal to the amount of heat the cold water absorbed.

(eq.

2)

When the amount of hot water released and cold water absorbed do not coincide, then it means the calorimeter is absorbing some of the heat. The amount of heat that is actually released depends to the mass, specific heat of the substance, and the change in temperature.

(Eq. 3)

(Eq. 7) (Eq. 8) are both used to calculate the heat of the solution and the heat of the calorimeter.

Hess’s Law is also an important concept in this lab. It states that the enthalpy of a reaction is independent of the steps it takes to go from reactant to a product. It happens because enthalpy is a state function. A state function depends on the initial and final state but not the actual process. The Hess’s Law is used to calculate the heat formation of Magnesium Oxide. The amount of heat necessary to create one more mole of a substance is called the Enthalpy of Formation.

(Eq. 78 de

Mg)