![]() #H_3COH(l) + H_2O(l) rarr H_3COH(aq)# (ii)Īs regards reaction (ii), we know that methanol is infinitely miscible with water (in fact if you rigorously dry methanol and then expose it to the air on a humid day, you can actually see the volume of the methanol expand as it absorbs air-borne moisture) nevertheless, this reaction is certainly physical inasmuch as no new bonds are formed (except for the very weak dispersion forces between methanol and water). The issue becomes much more ambiguous when we consider dissolution reactions. The designation of this reaction as a physical change is quite unambiguous. We could also write the equation in this form to show how energy transfers in the reaction:Ĭondensation of steam is thus recognized as an exothermic process, or alternatively, vaporization of water is an endothermic process. On the other hand when water is heated to give steam, or steam condensed to give water, no bonds are broken, but a change in state occurs. ![]() A new product is formed, and this equation is unambiguously a chemical change. Here both #H-H# and #Cl-Cl# bonds are broken, and #H-Cl# bonds are formed. For (i) it is easy to see which bonds are broken and which bonds are formed: So at the risk of starting a long, protracted argument, I'll give you my definitions, and try to supply examples of each.Ĭhemical change is characterized by the formation of new substances and the making and breaking of strong chemical bonds. There seems to be a lot of confusion in the classification of physical versus chemical change, and you will see a lot of differing answers on Socratic when a student asks is this particular reaction a physical or chemical reaction.
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