#### Related to [[Acids and bases]] and [[Rate laws]] --- ## Definitions - The **reaction mechanism of an equation** is the individual *usually small* kinetic steps that shows how each reaction occurs. - Most reactions occur in more than one step on a molecular level, each of these steps have their own k, they add up together to form the overall balanced equation and are called ***elementary steps.*** - Reaction **intermediaries** are compounds that are formed in elementary steps but ultimately react to form another compound and thus are **not present after all the elementary steps of a reaction have occurred**. In other words they are used in one step and consumed in another. >[!tip] >##### Rate determining step >- Remember that the rate law of a reaction is always determined **by the rate of the slowest elementary step within the reaction.** This step is known as the **rate determining step** >[!tip] >##### Types of steps >- A step involving only **one reactant molecule** is known as a *unimolecular step*. Steps involving two reactant molecules **including two of the same reactant molecules** are known as bimolecular steps, 3 - trimolecular and so on. --- ## Collision theory of reactions - This theory states that reactions occur through the collision of molecules. The more collisions there are the faster the rate of the reaction is. This is why increasing the temperature of a reaction increases the rate. - When two particles collide they have to be in the **correct orientation and must have enough speed/energy to react**. ##### Activation energy - The **activation energy of a chemical reaction** is the amount of energy needed to catalyze a reaction. When two species are mixed they may not have enough energy on their own to start reacting, **as a result energy needs to be added to the system, *this is done by increasing the heat***. - A catalyst is a chemical that **lower the activation energy needed to catalyze a reaction**. >[!quote] >![[Pasted image 20230301125905.png|800]] - Finding the activation energy of a reaction **requires experimentation** where you calculate the rate constant of the reaction at different **increasing temperatures**. --- ## Catalysts - A catalyst is a **substance that speeds up a reaction without being consumed by the reaction.** Catalysts can and **often will change the reaction pathway** introducing or removing certain elementary steps *without* changing the products of the reaction. - Note that **catalysis** is the use of catalysts to speed up reaction without changing the temperature. >##### Types of catalysts >- Homogeneous catalysts: These are catalysts that are in the **same phase** as the reactant. *(Meaning both the reactants and the catalysts are in the same state of matter; gas, liquid...)*. >- Heterogeneous catalysts are the opposite *they are in a different phase then the reactants*. Many oxidation reactions involve heterogeneous catalysts and catalytic converters are a type of heterogeneous catalyst since they are a solid that reacts with a gas *flowing out of an engine's exsaust.* --- #mainpage