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Encyclopedia > Exothermic reaction

In chemistry, an exothermic reaction is one that releases heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation: For other uses, see Chemistry (disambiguation). ... For other uses, see Heat (disambiguation) In physics, heat, symbolized by Q, is energy transferred from one body or system to another due to a difference in temperature. ... In Chemistry an endothermic reaction is one in which the reactants have less energy than the products, and thus a net input of energy, usually in the form of heat, is required. ... A chemical equation is a symbolic representation of a chemical reaction. ...

reactants → product + energy

Contents

Overview

In an exothermic reaction, the total energy absorbed in bond breaking is less than the total energy released in bond making. In other words, the energy needed for the reaction to occur is less than the total energy provided. 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. 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 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: t In thermodynamics and molecular chemistry, the enthalpy or heat content (denoted as H or ΔH, or rarely as χ) is a quotient or description of thermodynamic potential of a system, which can be used to calculate the useful work obtainable from a closed thermodynamic system under constant pressure. ... A calorimeter is a device used for calorimetry, the science of measuring the heat of chemical reactions or physical changes. ... This article is about the chemical reaction combustion. ...

ΔH = energy used in bond breaking reactions - energy released in bond making products
A sketch of an exothermic reaction
A sketch of an exothermic reaction

by definition the enthalpy change has a negative value:

ΔH < 0

For an exothermic reaction, this 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 → 2H2O
ΔH = -483.6 kJ/mol of O2

Examples of exothermic reactions

This article is about the chemical reaction combustion. ... Neutralization is a chemical reaction, also called a water forming reaction, in which an acid and a base or alkali (soluble base) react and produce a salt and water. ... As a general term, a substance is said to be anhydrous if it contains no water. ... Flash point non flammable Related Compounds Other cations Nickel(II) sulfate Zinc sulfate Except where noted otherwise, data are given for materials in their standard state (at 25 Â°C, 100 kPa) Infobox disclaimer and references Copper(II) sulfate (sulphate in most Commonwealth nations) is the chemical compound with the formula... A thermite mixture using Iron (III) Oxide A thermite mixture using Iron (II,III) Oxide Thermite is a kind of pyrotechnic composition of aluminium powder and a metal oxide which produces an aluminothermic reaction known as a thermite reaction. ... A self-heating can is an extension of the common food can. ... This article or section does not adequately cite its references or sources. ... Aluminum is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. ...

Key points

  • The concept and its opposite number endothermic relate to the enthalpy change in any process not just chemical reaction.
  • In endergonic reactions and exergonic reactions it is the sign of the Gibbs free energy that count and not enthalpy. the related concepts endergonic and exergonic apply to all physical processes.
  • the conceptually related endotherm and exotherm 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.

This article is about the physical effect. ... An endergonic reaction is a chemical reaction in which the change in free energy is positive. ... An exergonic reaction is a chemical reaction where the variation of free energy is negative. ... In thermodynamics, the Gibbs free energy is a thermodynamic potential which measures the useful work obtainable from a closed thermodynamic system at a constant temperature and pressure. ... t In thermodynamics and molecular chemistry, the enthalpy or heat content (denoted as H or ΔH, or rarely as χ) is a quotient or description of thermodynamic potential of a system, which can be used to calculate the useful work obtainable from a closed thermodynamic system under constant pressure. ... Endergonic means absorbing energy in the form of work. ... Look up exergonic in Wiktionary, the free dictionary. ... A warm-blooded (homeothermic) animal is one that can keep its core body temperature at a nearly constant level regardless of the temperature of the surrounding environment (that is, to maintain thermal homeostasis) . This can involve not only the ability to generate heat, but also the ability to cool down... A warm-blooded (homeothermic) animal is one that can keep its core body temperature at a nearly constant level regardless of the temperature of the surrounding environment (that is, to maintain thermal homeostasis) . This can involve not only the ability to generate heat, but also the ability to cool down...

See also

Endergonic means absorbing energy in the form of work. ... Look up exergonic in Wiktionary, the free dictionary. ... An endergonic reaction is a chemical reaction in which the change in free energy is positive. ... An exergonic reaction is a chemical reaction where the variation of free energy is negative. ... In thermodynamics, the word exothermic outside heating describes a process or reaction that releases energy usually in the form of heat, but it can also release energy in form of light (e. ... This article is about the physical effect. ... A warm-blooded (homeothermic) animal is one that can keep its core body temperature at a nearly constant level regardless of the temperature of the surrounding environment (that is, to maintain thermal homeostasis) . This can involve not only the ability to generate heat, but also the ability to cool down... A warm-blooded (homeothermic) animal is one that can keep its core body temperature at a nearly constant level regardless of the temperature of the surrounding environment (that is, to maintain thermal homeostasis) . This can involve not only the ability to generate heat, but also the ability to cool down...

External links

  • GCSE Science: Reactions

  Results from FactBites:
 
Exothermic reaction - an introduction - Citizendium (390 words)
In chemistry, an exothermic reaction is one that releases energy in the form of heat.
It is the opposite of an endothermic reaction.
For an exothermic reaction, this 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).
Lid for exothermic reaction welding mold - Patent 6776386 (2526 words)
A lid for an exothermic reaction mold device as set forth in claim 1 wherein said exhaust vent is perpendicular to said axis of said circular opening.
A lid for an exothermic reaction mold device as set forth in claim 1 wherein said crucible is connected to a mold cavity in said block by a passageway.
Exothermic reaction welding is a known procedure for joining connectors such as, but not limited to, stranded metal cable to each other and also to ground rods and other parts.
  More results at FactBites »

 
 

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