Effect of temperature on equilibrium.

[bucket]

Yeah this is probably a stupid question but I don't understand how and why temperature affects the value for K.
All my textbook says is:

As the temperature increases:

• for exothermic reactions, the amount of products decreases and so the value for K decreases
• for endothermic reactions, the amount of products increases and so the value for K increases

That sounds simple enough but I don't tend to remember things easily if I can't think about it logically, like why does this happen?
How does increasing the temperature cause the amount of products to decrease in exothermic reactions?

Yes, it probably shows that I haven't really done my homework, but.... ok I have no excuses.
Help!!
Please

[cara.mel]

Exothermic reactions release heat. Therefore as temperature goes up, it wants to, by le Chateleirs principle (I can't spell that name any more), want to try to make itself colder. Therefore it goes backwards to make more reactants (this uses up some of the added heat)

Vice versa for endothermic
Hope that makes some sort of sense

[bucket]

So what does adding more heat to the reactions do? =_=
damn i'm lost.

[lauzy358]

Humm.
If the reaction is exothermic it releases heat as reactants --> products.
Which means, if you add heat, the system will want to bring the temperature down, so to speak (i.e. oppose the change). [Le Chatelier's]
Since reactants --> products releases heat, in order to lower the temperature the system will go products --> reactants instead (a backwards reaction)
Like caramel says, this 'uses up' some of the added heat.
So the amount of products will decrease !

for aA + bB --> cC + dD
K = ([C]^c [D]^d) / ([A]^a [B ]^b) (sorry about the crappy setting out)
Products on top, reactants on the bottom.
So less products means a smaller K. (I always get confused with fractions so I sub in random numbers like 1/4 compared to 4/1 LOL ...yeah. << >>; )

& vice versa for endothermic.
Basically, what caramel said except said differently xp

Hope that helps!<3

[bucket]

basically what she said, but I actually understood that to some extent.
thankyou very much =]

[Collin Li]

Above is great, but don't get confused. Here's what some students reason when under pressure, or with little practice:

External change: Temperature increases

Therefore, the system wants to remove the excess energy.

Exothermic reaction means to release energy (less energy). The surroundings heat up.
Endothermic reaction means to absorb energy. The surroundings cool down (less energy).

Wait, so which one do we pick?

Make sure you distinguish between the system and the surroundings.

An increase in temperature increases the energy in the surroundings. Hence, the system would like to decrease the energy in the surroundings. To do so, it must absorb energy into the system (so system's energy will increase), so that the surroundings will lose some energy (the surrounding's energy will decrease -- the desired effect of Le Chatelier's Principle).