ENERGY AND CHEMICAL REACTION

The study of heat is called a thermochemical reaction that is part of the branch of a larger science of thermodynamics. Before talking about the principle of this thermochemical we proceed, will be made once the definition of some terms. One of the terms that will be used is the system. The system is part of the universe that we are studying. It may be for example a chemical reaction that occurs in a beaker. Outside the system is the environment. In explaining a system, we must analyze its properties appropriately. Given temperature, pressure, number of moles of each substance and a liquid, solid or gas. After all these variables are determined means that all the properties of the system is certain, we have described the state of the system.When changes occur in a system it is said that the system moves from one state to another state. When the system is isolated from the environment so that no heat can flow then changes that occur in the system is adiabatic change. During the adiabatic change, the temperature of the system will shift, when the exothermic reaction will go up while going down when the endothermic reaction. When the system was isolated from its environment, then the heat will flow between the two, so if there is a reaction, the temperature of the system can be made permanent. Changes that occur at constant temperature is called the change isotermik. It has been said, if the reaction is exothermic or endothermic then on the chemicals involved will be a change of potential energy. We measure the heat of reaction will be equal to the change of this potential energy. From now on we will use this change in some quantity that need to be enforced some rules to declare changes in general.The symbol Δ (Greek letter for delta) is generally used to indicate a change in quantity. For example changes in temperature can be written by ΔT, where T represents temperature. In practice, usually in the show change is by reducing the final temperature with the temperature at first.ΔT = Takhir - Tmula firstLikewise, changes in potential energy(Ep) Δ (E.P) = EPakhir - EPawalFrom this definition obtained an agreement in algebraic sign for exothermic and endothermic changes. In the exothermic change, the potential energy of the reaction is lower than the potential energy of reagents means lower than EPmula EPakhir first. So the price ÷ EP has a negative price. Opposite to the endothermic reaction, where the price ÷ EP is positive.Exothermic and endothermic reactions
 Endothermic event (right) and exothermic (left)Exothermic reactionExothermic reaction occurs at the heat transfer from the system into the environment or on the reaction heat is released. In the exothermic reaction ΔH = negative prices (-)Example:C (s) + O2 (g) → CO2 (g) + 393.5 kJ;ΔH = -393.5 kJEndothermic reactionIn reaction to the heat transfer occurs from the environment to the system or to the reaction heat is needed. At the price endothermic reaction ΔH = positive (+)