Thermochemistry: Calorimetry and Hess’s Law

1 January 2018

The main objective of the thermochemistry lab is to explore the first and second laws of thermodynamics through the use of a calorimeter during the reaction. A calorimeter is a device that is used for calorimetry to find the specific heat of a chemical reaction or a physical transition (Tro, 2015). A calorimeter is used to analyze the direction and magnitude of a substances’ temperature change to find the specific heat (Cs) of the substance. Specific heat is then used to refer to the amount of heat lost or gained when one gram of a substance either decreases or increases by one degree Celsius. The heat transfer is referred to a change in enthalpy of a reaction (qrxn). Change in enthalpy is related to the mass of the solution (m), the specific heat capacity of the solution (Cs), and the temperature change (?? = ?final — ?initial) through the equation qrxn= (mc • ??) (Risko, 2017). When finding the total heat transfer, the use of thermochemistry comes into play.

Thermochemistry is an area of chemistry that focuses on the study of heat energy that is associated with chemical reactions or physical transitions (Tro, 2015). Thermochemistry is based on a branch of chemistry called thermodynamics. Thermodynamics deals with energy and studies how the energy of an object or substance is able to do work. This is done by my means of the four laws of thermodynamics. The first and second law of thermodynamics is the laws that were focused on for the thermochemistry lab. The first law is the law of conservation of energy, which states that energy can be neither created nor destroyed (Tro, 2015) For example, when a chemical reaction takes place energy has to be put into the system in order for the reaction to begin. The energy used to start the reaction will be conserved and remain the end. The second law of thermodynamics states that the entropy of an isolated system will always increase over time (Tro, 2015). That is to say that energy will inevitably flow from a higher concentration to a lower concentration causing the entropy to reach an equilibrium point.

Thermochemistry is a useful concept to understand as it is used in many everyday household items. One product that comes to mind that uses this concept is Instant Hot and Cold Packs. Many instant hot and cold packs function by dissolving a salt in water. The ionic bonds of the salt then begin to separate. This processor system requires an input of energy, which is obtained from the surroundings. The ions then form bonds with the water, a process that releases energy, or begins an exothermic reaction (Risko, 2017). These hot and cold packs eventually cool down which is an example of the second law. An example of an endothermic reaction which uses thermochemistry is melting ice cubes. As an ice cube is encompassed by warm surroundings, the energy wants to flow from high concentration to low concentration. As the heat begins to penetrate the ice cube, it will begin to warm and melt until it comes to an equilibrium where the ice cube has become the same temperature as the surroundings. This endothermic process will be analyzed closer in this lab.

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