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# unit 2 help watch

1. when temp increases for reversible reaction, why does it shift to endothermic direction ? anyone?
2. (Original post by SennaRacer77)
when temp increases for reversible reaction, why does it shift to endothermic direction ? anyone?
the equilibrium always shifts to minimise the effect of the change (Le Chatelier's principle). So if you have an endothermic forward reaction, it will move further over to the right when you increase temperature. In an exothermic reaction, the opposite is the case.

similarly, if you have a reaction with fewer numbers of molecules on the right (say N2 + 3H2 --> 2NH3), increasing the pressure will push the equilibrium over to the right (and vice versa).
3. yup i know its the principle. but i dun get why temp increase why is it endo instead of exo?
4. (Original post by Plato's Trousers)
the equilibrium always shifts to minimise the effect of the change (Le Chatelier's principle). So if you have an endothermic forward reaction, it will move further over to the right when you increase temperature. In an exothermic reaction, the opposite is the case.

similarly, if you have a reaction with fewer numbers of molecules on the right (say N2 + 3H2 --> 2NH3), increasing the pressure will push the equilibrium over to the right (and vice versa).
only if the molecules are gaseous. I almost got caught out by not reading state symbols a couple of weeks ago
5. (Original post by SennaRacer77)
yup i know its the principle. but i dun get why temp increase why is it endo instead of exo?
if you increase the temperature it is independent of whether the reaction is endo- or exo- themic. these 2 terms refer to the "enthalpy change" or thermal energy released or absorbed during a reaction. whatever you do to the general temperature in the system wont affect whether the reaction is endothermic or not. (I think this is what you were asking, dunno though)
6. Just learn that endothermic reactions favour an increase in temperature and exothermic reactions favour low temperatures (temperature decreases). Thats what we have been taught.
7. (Original post by SennaRacer77)
yup i know its the principle. but i dun get why temp increase why is it endo instead of exo?
If you increase the temperature, according to the principle, the equilibrium will change to try and decrease the temperature thus the endothermic reaction, ie reaction requiring energy, will be favoured.
8. Yeah within a closed system, according to Le Chateliers principle any change in conditions will cause the equilibrium to change in order to 'absorb' the change. You increase the temperature of the vessel you are reacting chemicals at equilibrium in, the endothermic direction of the equilibrium will be favored as this lowers the temperature of the vessel and is thus 'absorbing' the change.

Basically...the system tries to stay at a constant environment:
-So an INCREASE in temp causes ENDOTHERMIC reactions to keep the temperature constant.
- A DECREASE in temp causes EXOTHERMIC reactions to keep temp constant.
- An INCREASE in pressure causes more reactions that favor the side of the reaction with less moles of gas...in order to reduce the pressure. And return to that constant pressure.

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