Exothermic reaction

chemical reaction

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stay chemical reaction Medium, reactant Total energy greater than Product The reaction of total energy is called exothermic reaction. Including combustion, neutralization, metal oxidation Thermite reaction Reactions between more active metals and acids, from unstable substances to stable substances.

Chinese name: Exothermic reaction
Foreign name: exothermic reaction

Interpretation: The total energy before reaction is greater than that after reaction
Reaction type: burning , neutralization, metal oxidation, aluminothermic reaction
Common reactions: Acid base neutralization reaction, combustion reaction

catalog

one Reaction principle
two Reaction type
three Common reactions
four Relationship between four basic reaction types and exothermic reaction

Reaction principle

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Exothermic reaction

The total energy before reaction is greater than the total energy after reaction chemical reaction It's called exothermic reaction^[1]

△ H=reactant bond energy product bond energy

Reaction type

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Combustion, neutralization, metal oxidation Thermite reaction The reaction of more active metals with acids and the reaction from unstable substances to stable substances are mostly exothermic (but we should note that the transformation of graphite into diamond under high pressure is exothermic, although it is the opposite under normal pressure), and most decomposition reactions are endothermic (but they cannot be absolute, for example, the decomposition of potassium chlorate into potassium chloride and oxygen is a common exothermic reaction) Spontaneous Redox reaction All are exothermic reactions. The combustion reaction and neutralization reaction in common reactions are exothermic reactions, acid base neutralization reaction, metal acid reaction, metal water reaction, combustion reaction and explosion reaction, which are all exothermic reactions. In specific judgment, it is often necessary to combine the facts in memory. Exothermic Reverse reaction By all means Endothermic reaction 。^[2]

Common reactions

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(1) All combustion or explosion reactions.

(2) Acid base neutralization reaction.

Exothermic reaction

(3) Most chemical reactions.

(4) Active metal generates H with water or acid two Reaction.

(5) Many Redox reaction (but not absolute). Such as hydrogen, charcoal or Reduction of copper oxide by carbon monoxide Are typical exothermic reactions.

(6) NaOH or concentrated sulfuric acid is dissolved in water (Note: these two points only mean exothermic, but strictly speaking, they are not chemical reactions, and should be noted during the exam)

Relationship between four basic reaction types and exothermic reaction

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Combination reaction

Most chemical reactions are exothermic

The formation reaction of hydride is exothermic

For example, hydrogen and fluorine explode in the dark: H two +F two =2HF

The formation of 2 oxides is exothermic reaction

For example, burning charcoal in air or oxygen gives off heat: C+O two = CO two

3 Formation reaction of oxyacid

for example Sulfur trioxide Dissolving in water to generate sulfuric acid is an exothermic reaction: SO three +H two O=H two SO four

4 The formation reaction of strong base is exothermic

For example, sodium oxide reacts with water to form sodium hydroxide Heat release: Na two O+H two O=2NaOH

decomposition reaction

Few decomposition reactions are exothermic

For example, ammonium nitrate decomposes when heated or impacted and explodes. Exothermic reaction: 2NH four NO three =2N two ↑+O two ↑ +4H two O

Displacement reaction

Most displacement reactions are exothermic

1 Example of exothermic reaction between active metal and water

Reaction of metal sodium with water

Exothermic reaction of sodium and water: 2Na+2H two O=2NaOH+H two ↑

2. Examples of exothermic reaction between active non-metal and water

Heat release during displacement reaction of fluorine gas and water: 2F two +2H two O→4HF+O two

3 Simple aluminum and some metallic oxide Examples of exothermic reactions occurring

Aluminum powder and manganese dioxide Heat release during displacement reaction: 4Al+3MnO two =2Al two O three + 3Mn

4 Example of exothermic displacement reaction between active metal and acid

Exothermic reaction of metal sodium and hydrochloric acid: 2Na+2HCl=2NaCl+H two ↑

Metathesis reaction

Acid base neutralization reaction is exothermic

Neutralization reaction of hydrochloric acid and sodium hydroxide solution

The reaction between hydrochloric acid and sodium hydroxide solution is exothermic: HCl+NaOH=NaCl+H two O

How to distinguish

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The essence of chemical reaction is: the breaking of old bonds and the formation of new bonds, and the newly formed chemical bonds are generally more stable than the old bonds. The covalent electrons jump from the high energy level to the low energy level and release energy, while the breaking of the old bonds needs to absorb energy, so whether the final chemical reaction is endothermic or exothermic depends on the difference in energy changes before and after the reaction. If the energy is insufficient, it needs to absorb heat from the outside, otherwise it needs to release heat, Usually we use enthalpy change (△ H) to measure the thermal phenomenon before and after the reaction^[3]

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