Effect of catalyst

[IreneSeo3F]

Can someone explain why the deltaH(rxn) is not different between catalyzed and uncatalyzed reactions?

[Jessie Hsu 1C]

Delta H is the difference between the enthalpies of the reactants and the products. A catalyst lowers the activation energy ( lowers the peak you see on enthalpy vs rxn graphs), but doesn't change the enthalpies of the reactants and products, meaning delta H doesn't change either.

[Arya Adibi 1K]

when you look at the plot of enthalpy vs reaction progression, the reactants and products do not shift in the presense of a catalyst. A catalyst just lowers the peak of the activation energy.

[Sharon Kim 2A]

The reason why the catalyst wouldn't change the enthalpy is because it is a state function function. The catalyst changes the pathway of the reason thus lowering the activation energy and increasing the rate constant. So it is just making the reaction go faster to its final state.

[605291562]

Hi! Enthalpy doesn't change because it is a state function (so it only matters where it starts and ends not the path it takes) the best way for me to think of catalysts is everything stays the same it just takes a path with a lower activation energy, so it does not affect the enthalpy.

[Joshua_Chan_3K]

The catalyzed reaction just changes the pathway which includes the activation energy. Since its a state function you can see that the the starting components and the final products are the same as the original reaction. Since the start and end are the same, delta H doesn't change.

[Annette Fishman]

The uncatalyzed reaction proceeds via a one-step mechanism (one transition state observed), whereas the catalyzed reaction follows a two-step mechanism (two transition states observed) with a notably lesser activation energy. Enthalpy is a state function, so we are only focusing on final minus initial. This means that it will not change while activation energy does.

[gabbi_r2C]

I think it has mostly to do with how the catalyst changes the path of the reaction, but delta H is a state function and doesn't depend on the path taken. if you look at some of the graphs we did in lecture, its only the activation energy that is lowered with a catalyst, not the actual energy of the reactants and products (which is what determines delta H, hence why it doesn't change).

[Karina Grover 1A]

Catalysts only affect the activation energy barrier (the hump). They lower the activation energy barrier so that the reaction can occur at a faster rate. In doing so, rate constants increase in value. Thus, it does not affect the enthalpy difference between reactants and products.

[Ziyan Peng 3A]

delta H doesn't change in the presence of a catalyst. the catalyst just gives the reaction an alternate pathway with a lower activation energy. It's like going through a tunnel vs climbing the mountain to get to the other side.

[FrancescaHawkins2H]

A catalyst only changes the pathway taken to get from reactants to products, by lowering the activation energy needed for the reaction to occur. It does not, however, change the state of the products or reactants, and thus does not change delta H. Hope that makes sense!

[Eve Gross-Sable 1B]

Delta H does not have to do with the activation energy, but rather it is the change in enthalpy from the reactants to products in the most direct path on the graph (excluding the hump). So it's the net, and therefore the activation energy does not affect it. Because the catalyst lowers the activation energy of the reaction, it won't affect deltaH.

[AndrewNguyen_2H]

If you look at a diagram, you'll see that the starting and final potential energies are the same.

[Jaden Joodi 3J]

The catalyst does not change the amount of heat absorbed or given off for a reaction. It only lowers the activation energy required to activate the reaction

[rhettfarmer-3H]

Catalyst do not affect H because H is dependent on the formation of product and reactant and a catalyst cannot change those properties.

[Kelly Ha 1K]

Catalysts speed up the reaction (increasing k) by lowering the activation energy. Although catalysts provide a new pathway for the reaction, they don't affect the reaction thermodynamically such as altering ΔG or ΔH.

[Abhinav Behl 3G]

Adding a catalyst will speed up a reaction by reducing its activation energy, thus resulting in a new, shorter pathway for the reactants to form products. However, since ΔH is a state function, it won't change in value when you speed up/slow down a reaction, because it doesn't depend on the pathway. So, whether a reaction is catalyzed or uncatalyzed, it will not affect the ΔH of the reaction.

[Adrienne Chan 1G]

Catalysts merely increase the rate of a reaction by lowering the activation energy. This does not affect the overall heat of reaction, as the products and reactants are still the same in the end. You can think of it like an enzyme if that helps!

[sophia kosturos 2B]

catalysts speed up a reaction by lowering the activation energy, however, it does not have any effect on the thermodynamics of an equation, thus why the delta H is not affected.

[Taha 2D]

because it doesnt change enthaplies. the difference in energies remain the same, only the activation energy peak is brought down

[Shrinidhy Srinivas 3L]

Personally, I think the best way to think about this is by using a reaction profile. When a catalyst is added to a reaction, the bump goes down as the catalyst makes it so that not as much energy is needed to get to the final result. However, this makes no difference to the state of the reactants and products with regards to their delta G. Make sure not to confuse thermodynamics and kinetics!

[LovepreetSran_3H]

catalyst only affects the pathway taken, it does not change the states of the products and reactants.

[reyvalui_3g]

A catalyst will only affect the pathway taken in a reaction.