Enthalpy change of reaction
Introduction:
Thermochemistry is the branch of chemistry that studies the energy and heat associated with chemical reactions and/or physical transformations. A reaction may release or absorb energy, and a phase may change, such as in melting and boiling. Thermochemistry focuses on these energy changes, particularly on the system 's energy exchange with its surroundings. In combination with entropy determinations, it is used to predict whether a reaction is spontaneous or non-spontaneous, favourable or unfavourable.
Chemical reactions can be divided into two based on the energy changes that occur during the reaction which are endothermic and exothermic reactions. Endothermic reaction is a chemical reaction that absorbs heat energy from the surrounding. Hence, it has a positive value for enthalpy change of reaction. In contrary, exothermic reaction is a chemical reaction that releases heat energy to the surroundings, resulting in a negative value for enthalpy change of reaction.
Enthalpy change of a reaction is the heat energy change in a chemical reaction, for the number of moles of reactants shown in the chemical equation. Standard enthalpy of reaction, ΔrH⊖ is the enthalpy change that occurs in a system when one mole of matter is transformed by a chemical reaction under standard conditions.
Enthalpy change of reaction has an interrelationship with Hess’ Law which states that the total enthalpy change during the complete course of a reaction is same whether the reaction is made in one step or in several steps. In other words, if a chemical change takes place by several different routes, the overall enthalpy change is the same, regardless of the route by which the chemical change occurs provided the initial and final condition are the same.
The purpose of this experiment are to measure and compare the amount of heat change involved in three separate but related reactions and to study the experimental verification of Hess’ Law.
Experiment 10
Enthalpy
Thermochemistry is the branch of chemistry that studies the energy and heat associated with chemical reactions and/or physical transformations. A reaction may release or absorb energy, and a phase may change, such as in melting and boiling. Thermochemistry focuses on these energy changes, particularly on the system 's energy exchange with its surroundings. In combination with entropy determinations, it is used to predict whether a reaction is spontaneous or non-spontaneous, favourable or unfavourable.
Chemical reactions can be divided into two based on the energy changes that occur during the reaction which are endothermic and exothermic reactions. Endothermic reaction is a chemical reaction that absorbs heat energy from the surrounding. Hence, it has a positive value for enthalpy change of reaction. In contrary, exothermic reaction is a chemical reaction that releases heat energy to the surroundings, resulting in a negative value for enthalpy change of reaction.
Enthalpy change of a reaction is the heat energy change in a chemical reaction, for the number of moles of reactants shown in the chemical equation. Standard enthalpy of reaction, ΔrH⊖ is the enthalpy change that occurs in a system when one mole of matter is transformed by a chemical reaction under standard conditions.
Enthalpy change of reaction has an interrelationship with Hess’ Law which states that the total enthalpy change during the complete course of a reaction is same whether the reaction is made in one step or in several steps. In other words, if a chemical change takes place by several different routes, the overall enthalpy change is the same, regardless of the route by which the chemical change occurs provided the initial and final condition are the same.
The purpose of this experiment are to measure and compare the amount of heat change involved in three separate but related reactions and to study the experimental verification of Hess’ Law.
Experiment 10
Enthalpy
References: Internet: http://en.wikipedia.org/wiki/Exothermic_reaction http://www.s-cool.co.uk/a-level/chemistry/chemical-energetics/revise-it/enthalpy-changes http://chemwiki.ucdavis.edu/Physical_Chemistry/Thermodynamics/State_Functions/Enthalpy/Heat_of_Reaction Chapter Yew Lee, Loh. 2004.Chemical energetics. STPM Physical Chemistry Volume 2, ed N.Sivaneson. 349 & 350. Selangor ; Penerbitan Pelangi SDN. BHD. You Sie, Lim. 2007.Thermochemstry. In Pre-U Text STPM Physical Chemistry, ed. Kim Hong, Yip, 202--201,290-- 293. 374 &375. Rawang : Pearson Malaysia SDN. BHD.