Chemical Forums

Chemistry Forums for Students => High School Chemistry Forum => Topic started by: TNT_ on February 19, 2006, 08:49:50 AM

Title: endothermic:is this reaction endothermic???
Post by: TNT_ on February 19, 2006, 08:49:50 AM

are all thermal decomposition reactions ie.those which require heat to break down the reactant into the products, endothermic???? please *delete me*! ???

For example the reaction,
NaHC03>>NaCl+H20+C02

is this endothermic?

or are endothermic reactions only those which take in heat spontaneously(at room temp)?

Title: Re:endothermic:is this reaction endothermic???
Post by: shelanachium on February 19, 2006, 04:06:24 PM

The reaction 2NaHCO3 -> Na2CO3 + H2O + CO2 is indeed endothermic and requires heat, as are many others that only occur on heating.

But not all, for combustion, a highly exothermic reaction, needs heat to start it when, as is usual, strong bonds in the reactants must first be broken. This first step is endothermic and so requires heat, but subsequent steps release more heat than was required to start the reaction. Reactions like these are usually self-sustaining once begun, as in flames and explosions.

In an endothermic reaction heat must be continuously supplied and the reaction is not self-sustaining. Stop heating NaHCO3 and the decomposition will slow down and stop.