how can we identify that a chemical equation has taken place
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A chemical reaction is connected with - what is most important - changes in energy states and changes in structure. The signs are as follows:
Change of temperature - the mixture cools down or heats up. This sign alone is not enough, as dissolution of some substances causes a similar effect (dissolution of sulfuric acid in water causes a temperature elevation, and dissolving of sodium thiocyanate cools the mixture down)
Change of colour - not the shade, but the colour itself. When making dibenzylideneacetone, upon mixing colourless substrates you get a bright yellow product
Emission of gas - meaning something gets liberated. Sometimes it will be effervescence - like upon reaction of sodium with alcohol, which generates gaseous hydrogen - and sometimes it will be a smell appearing - like hydrogen sulfide being liberated from its salts, and giving the aroma of rotten eggs.
Forming of precipitates - if you mix two liquids, and suddenly solids appear, this means you had a reaction. Mix sodium chloride solution with silver nitrate and you’ll get a white precipitate.
Change of temperature - the mixture cools down or heats up. This sign alone is not enough, as dissolution of some substances causes a similar effect (dissolution of sulfuric acid in water causes a temperature elevation, and dissolving of sodium thiocyanate cools the mixture down)
Change of colour - not the shade, but the colour itself. When making dibenzylideneacetone, upon mixing colourless substrates you get a bright yellow product
Emission of gas - meaning something gets liberated. Sometimes it will be effervescence - like upon reaction of sodium with alcohol, which generates gaseous hydrogen - and sometimes it will be a smell appearing - like hydrogen sulfide being liberated from its salts, and giving the aroma of rotten eggs.
Forming of precipitates - if you mix two liquids, and suddenly solids appear, this means you had a reaction. Mix sodium chloride solution with silver nitrate and you’ll get a white precipitate.
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