Exothermic+Reaction

An exothermic reaction is a chemical reaction that is accompanied by the release of heat. In other words, the energy needed for the reaction to occur is less than the total energy released. As a result of this, the extra energy is released, usually in the form of heat. When using a [|calorimeter], the change in heat of the calorimeter is equal to the opposite of the change in heat of the system. This means that when the medium in which the reaction is taking place gains heat, the reaction is exothermic. The absolute amount of energy in a chemical system is extremely difficult to measure or calculate. The [|enthalpy] change, ΔH, of a chemical reaction is much easier to measure and calculate. A [|bomb calorimeter] is very suitable for measuring the energy change, ΔH, of a [|combustion] reaction. Measured and calculated ΔH values are related to bond energies by: ΔH = energy used in bond breaking reactions − energy released in bond making products An [|energy profile] of an exothermic reaction  Many chemical reactions release energy in the form of heat, light, or sound. These are exothermic reactions. Exothermic reactions may occur spontaneously and result in higher randomness or entropy (ΔS > 0) of the system. They are denoted by a negative heat flow (heat is lost to the surroundings) and decrease in enthalpy (ΔH < 0). In the lab, exothermic reactions produce heat or may even be explosive. by definition the enthalpy change has a negative value: ΔH < 0 in an exothermic reaction, gives a negative value for ΔH, since a larger value (the energy released in the reaction) is subtracted from a smaller value (the energy used for the reaction). For example, when hydrogen burns: 2H2 + O2 → 2H2OΔH = −483.6 kJ/mol of O2