Soul_Khan's Unit 4 chem thread

[Soul_Khan]

First question.. can someone please explain to me how catalysts work I know that they decrease the activation energy but how?

[Kanon]

First question.. can someone please explain to me how catalysts work I know that they decrease the activation energy but how?

From my understanding a catalyst doesn't decrease the reactants activation energy, rather provides them with an altnerative route that has a lowered activiation energy.  How does the catalyst lower the activation energy?  Not entirely sure, but I think it has something to do with the adsorbtion the reactants face when adsorbing to the stationary phase catalysts surface, probably aligning the reactants atoms in specific ways.

[Graphite]

The catalyst participates in bonding, weakening the bonds within the reactants. Thus, less energy is required to break them.

[Soul_Khan]

How come only a temperature change can change the value of K?

What happens when a chemical reaction is reversed and why? What happens when a chemical reaction is halved and why?

[FlorianK]

Let's say you have an endothermic reaction in equilibrium.
When you heat it up more products will be formed, because it wants to oppose the change in temperture.
It will still be in equilibrium then, but K will be changed.

[Soul_Khan]

Yer I know. But why does the value of K change when you change the temperature but doesn't change when you change the pressure or concentration.

[Jenny_2108]

Yer I know. But why does the value of K change when you change the temperature but doesn't change when you change the pressure or concentration.

If you change the concentration of reactants/products or volume/pressure, the system will adjust itself until the equilibrium ration is reestablished at the K value

Increasing temperature will favour the endothermic over the exothermic direction. Hence, rate of endothermic process increases and the equilibrium reestablished with new concentrations due to more the endothermic products => K value changes

[FlorianK]

Changing the pressure (by changing the volume of the system) changes the concentration and then the sytem will try to oppose the change and bring back the old ratio of concentrations. [same ratio of concentration as before the change
Changing the temperature doesn't change the concentrations. The system will change the concentrations by making more products or reactants to oppose the change in temperature (different ratio of concentration as before the change)