Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: Alison on 11/10/2009 13:30:03

Title: Are most reactions exothermic?
Post by: Alison on 11/10/2009 13:30:03

Alison asked the Naked Scientists:
   
Are most reactions exothermic? If so why do we use the bunsen so much in the lab?

What do you think?

Title: Are most reactions exothermic?
Post by: Bored chemist on 11/10/2009 14:29:01

All reactions are exothermic- in one direction. They are exactly as endothermic in the other direction.
One reason for heating things up in the lab is to get things to react more quickly.

Title: Are most reactions exothermic?
Post by: lightarrow on 11/10/2009 18:38:47

Quote from: Bored chemist on 11/10/2009 14:29:01

All reactions are exothermic- in one direction. They are exactly as endothermic in the other direction.
One reason for heating things up in the lab is to get things to react more quickly.

...which has not only to do with the enthalpy variation in the reaction, but with lowering the activation energy too.

Title: Are most reactions exothermic?
Post by: Horseradish_5000 on 20/10/2009 18:37:45

most reaction are exothermic and the bunsen is used to reach the activation energy so it can start.

Title: Are most reactions exothermic?
Post by: lightarrow on 20/10/2009 20:31:01

Anyway, many common reactions are endothermic: fusion, vaporization, sublimation, for example.

Title: Are most reactions exothermic?
Post by: Bored chemist on 21/10/2009 18:55:05

It's a moot point if phase changes are "reations".


An important reason why some reactios run a lot faster when heated is that one of the reactants melts. Two solids can only react at the points where they are in contact. If you heat them and one melts then it can flow over the other and so there's more contact area.