All Topics  
Exothermic reaction

 

 
   Email Print
   Bookmark   Link
 

 

Exothermic reaction
 
 
  Topics Exothermic reaction Topic Home

An exothermic reaction is a chemical reaction
Chemical reaction

A chemical reaction is a process that always results in the interconversion of chemical substances. The substance or substances initially involved in a chemical reaction are called reactants....
 that releases energy in the form of heat
Heat

In physics and thermodynamics, heat is any transfer of energy from one body or thermodynamic system to another due to a difference in temperature....
. It is the opposite of an endothermic reaction. Expressed in a chemical equation
Chemical equation

A chemical equation may be described as a chemical reaction or a means of writing out and describing such a phenomenon. The coefficients next to the symbols and formulae of entities are the absolute values of the stoichiometric coefficient....
:

reactants ? products + energy


Overview
An exothermic reaction is a chemical reaction accompanied by the release of heat. In other words, the energy needed for the reaction to occur is less than the total energy released.






Discussion
Ask a question about 'Exothermic reaction'
Start a new discussion about 'Exothermic reaction'
Answer questions from other users
Full Discussion Forum



Encyclopedia


An exothermic reaction is a chemical reaction
Chemical reaction

A chemical reaction is a process that always results in the interconversion of chemical substances. The substance or substances initially involved in a chemical reaction are called reactants....
 that releases energy in the form of heat
Heat

In physics and thermodynamics, heat is any transfer of energy from one body or thermodynamic system to another due to a difference in temperature....
. It is the opposite of an endothermic reaction. Expressed in a chemical equation
Chemical equation

A chemical equation may be described as a chemical reaction or a means of writing out and describing such a phenomenon. The coefficients next to the symbols and formulae of entities are the absolute values of the stoichiometric coefficient....
:

reactants ? products + energy


Overview


An exothermic reaction is a chemical reaction 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
Calorimeter

| |}A calorimeter is a device used for calorimetry, the science of measuring the heat of chemical reactions or physical changes as well as heat capacity....
, 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
Enthalpy

In thermodynamics and chemistry, the enthalpy is a quotient or description of thermodynamic potential of a system, which can be used to calculate the heat transfer during a quasistatic process taking place in a closed system thermodynamic system under constant pressure....
 change, ?H, of a chemical reaction is much easier to measure and calculate. A bomb calorimeter is very suitable for measuring the energy change, ?H, of a combustion
Combustion

Combustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames, appearance of light flickering....
 reaction. Measured and calculated ?H values are related to bond energies by:

?H = energy used in bond breaking reactions - energy released in bond making products


by definition the enthalpy change has a negative value:

?H < 0


For an exothermic reaction, this gives a negative value for ?H, 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 ? 2H2O
?H = -483.6 kJ/mol of O2


Examples of exothermic reactions

  • Combustion
    Combustion

    Combustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames, appearance of light flickering....
     reactions of fuel
    Fuel

    Fuel is any material that is burned or altered in order to obtain energy and to heat or to move an object. Fuel releases its energy either through a chemical reaction means, such as combustion, or nuclear means, such as nuclear fission or nuclear fusion....
    s
  • Neutralization reactions such as direct reaction of acid and base
  • Adding concentrated acid to water
  • Adding water to anhydrous
    Anhydrous

    As a general term, a substance is said to be anhydrous if it contains no water. The way of achieving the anhydrous form differs from one substance to another....
     copper(II) sulfate
    Copper(II) sulfate

    Copper sulfate is the chemical compound with the chemical formula CopperSulfurOxygen4. This salt exists as a series of compounds that differ in their degree of water of crystallization....
  • The Thermite
    Thermite

    Thermite is a pyrotechnic composition of a metal powder and a metal oxide, which produces an aluminothermic reaction known as a thermite reaction....
     reaction
  • Reactions taking place in a self-heating can
    Self-heating can

    A self-heating can is an enhancement of the common food canning. Self-heating cans have dual chambers, one surrounding the other. The inner chamber holds the food or drink, and the outer chamber houses chemicals that undergo an exothermic reaction when combined....
     based on lime
    Lime (mineral)

    Lime is a general term for calcium-containing inorganic materials, in which carbonates, oxides and hydroxides predominate. Strictly speaking, lime is calcium oxide or calcium hydroxide....
     and aluminum
  • The setting of cement
    Cement

    In the most general sense of the word, a cement is a binder, a substance which sets and hardens independently, and can bind other materials together....
     and concrete
    Concrete

    Concrete is a construction material composed of cement as well as other cementitious materials such as fly ash and slag cement, construction aggregate , water , and Chemistry admixtures....
  • Many corrosion
    Corrosion

    Corrosion means the breaking down of essential properties in a material due to chemical reactions with its surroundings. In the most common use of the word, this means a loss of electrons of metals reacting with water and oxygen....
     reactions such as oxidation of metals
  • Most polymerisation reactions
  • The Haber-Bosch process
    Haber process

    The Haber process, also called the Haber?Bosch process, is the nitrogen fixation reaction of nitrogen and hydrogen, over an enriched iron Catalysis, to produce ammonia....
     of ammonia production
    Ammonia production

    Because of its many uses, ammonia is one of the most highly-produced inorganic chemicals. There are numerous large-scale ammonia production plants worldwide, producing a total of 109,000,000 metric tons of ammonia in 2004....


Key points

  • The concept and its opposite number endothermic
    Endothermic

    In thermodynamics, the word endothermic "within-heating" describes a process or reaction that absorbs energy in the form of heat. Its etymology stems from the Greek prefix endo-, meaning ?inside? and the Greek suffix ?thermic, meaning ?to heat?....
     relate to the enthalpy change in any process, not just chemical reactions.
  • In endergonic reaction
    Endergonic reaction

    In thermochemistry, an endergonic reaction is a chemical reaction in which the standard change in Thermodynamic free energy is positive, and energy is absorbed....
    s and exergonic reaction
    Exergonic reaction

    An exergonic reaction is a chemical reaction where the change in the Gibbs free energy is negative, indicating a spontaneous reaction. Symbolically, the release of Gibbs free energy, G, in an exergonic reaction is denoted as...
    s it is the sign of the Gibbs free energy
    Gibbs free energy

    In thermodynamics, the Gibbs free energy is a thermodynamic potential that measures the "useful" or process-initiating Work obtainable from an isothermal, Isobaric process thermodynamic system....
     that determines the equilibrium point, and not enthalpy
    Enthalpy

    In thermodynamics and chemistry, the enthalpy is a quotient or description of thermodynamic potential of a system, which can be used to calculate the heat transfer during a quasistatic process taking place in a closed system thermodynamic system under constant pressure....
    . The related concepts endergonic
    Endergonic

    Endergonic means absorbing energy in the form of work. Its etymology stems from the suffix -ergonic, as derived from the Greek root ergon, meaning work , combined with the prefix end-, as derived from the Greek root en, meaning put into....
     and exergonic
    Exergonic

    Exergonic means to release energy in the form of work. Its etymology stems from the suffix -ergonic, as derived from the Greek root ergon, meaning work , combined with the Greek prefix ex-, meaning out of....
     apply to all physical processes.
  • the conceptually related endotherm
    Warm-blooded

    In biology, a warm-blooded animal species is one whose members maintain thermal homeostasis; that is, they keep their body temperature at a roughly constant level, regardless of the ambient temperature....
     and exotherm
    Warm-blooded

    In biology, a warm-blooded animal species is one whose members maintain thermal homeostasis; that is, they keep their body temperature at a roughly constant level, regardless of the ambient temperature....
     are concepts in Animal physiology.
  • In quantum numbers, when any exited energy level goes down to its original level for example: when n=4 fall to n=2, energy is released so, it is exothermic.
  • Where an exothermic reaction causes heating of the reaction vessel which is not controlled, the rate of reaction can increase, in turn causing heat to be evolved even more quickly . This positive feedback situation is known as thermal runaway
    Thermal runaway

    File:ThermalRunaway.pngThermal runaway refers to a situation where an increase in temperature changes the conditions in a way that causes a further increase in temperature leading to a destructive result....
    . An Explosion
    Explosion

    An explosion is a sudden increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases....
     can also result from the problem.


Measurement

Heat production or absorption in either a physical process or chemical reaction is measured using calorimetry
Calorimetry

Calorimetry is the science of measuring the heat of chemical...
. One common laboratory instrument is the Differential scanning calorimeter or DSC, where a small sample is slowly heated in a controlled way and the heat flow into or from the sample chamber is monitored. The technique can be used to follow chemical reactions as well as physical processes, such as melting and boiling (both of which are endothermic
Endothermic

In thermodynamics, the word endothermic "within-heating" describes a process or reaction that absorbs energy in the form of heat. Its etymology stems from the Greek prefix endo-, meaning ?inside? and the Greek suffix ?thermic, meaning ?to heat?....
). Crystallization and condensation, the reverse processes, are both exothermic.

See also

  • Chemical thermodynamics
    Chemical thermodynamics

    Chemical thermodynamics is the study of the interrelation of heat and thermodynamic work with chemical reactions or with physical changes of thermodynamic state within the confines of the laws of thermodynamics....
  • Differential scanning calorimetry
    Differential scanning calorimetry

    Differential scanning calorimetry or DSC is a thermal analysis technique in which the difference in the amount of heat required to increase the temperature of a sample and reference are measured as a function of temperature....
  • Endergonic
    Endergonic

    Endergonic means absorbing energy in the form of work. Its etymology stems from the suffix -ergonic, as derived from the Greek root ergon, meaning work , combined with the prefix end-, as derived from the Greek root en, meaning put into....
  • Exergonic
    Exergonic

    Exergonic means to release energy in the form of work. Its etymology stems from the suffix -ergonic, as derived from the Greek root ergon, meaning work , combined with the Greek prefix ex-, meaning out of....
  • Endergonic reaction
    Endergonic reaction

    In thermochemistry, an endergonic reaction is a chemical reaction in which the standard change in Thermodynamic free energy is positive, and energy is absorbed....
  • Exergonic reaction
    Exergonic reaction

    An exergonic reaction is a chemical reaction where the change in the Gibbs free energy is negative, indicating a spontaneous reaction. Symbolically, the release of Gibbs free energy, G, in an exergonic reaction is denoted as...
  • Exothermic
    Exothermic

    File:Explosion1.JPG In thermodynamics, the term exothermic describes a process or reaction that releases energy usually in the form of heat, but also in form of light , electricity , or sound....
  • Endothermic
    Endothermic

    In thermodynamics, the word endothermic "within-heating" describes a process or reaction that absorbs energy in the form of heat. Its etymology stems from the Greek prefix endo-, meaning ?inside? and the Greek suffix ?thermic, meaning ?to heat?....
     reaction
  • Endotherm
    Warm-blooded

    In biology, a warm-blooded animal species is one whose members maintain thermal homeostasis; that is, they keep their body temperature at a roughly constant level, regardless of the ambient temperature....
  • Exotherm
    Cold-blooded

    Cold-blooded is a loose layman's term that may refer to:* ectothermic organisms* poikilothermic organismsCold-blooded could also refer to:...


External links