Catalysis — Revision Notes

⚡ 30-Second Revision

Catalyst: — Alters reaction rate, not consumed.\n- **Activation Energy ($E_a$):** Catalysts lower $E_a$, speeding up reaction.\n- Equilibrium: Catalysts do NOT change equilibrium constant ($K_{eq}$) or position.\n- Thermodynamics: Catalysts do NOT change $\Delta H$ or $\Delta G$.\n- Homogeneous Catalysis: Catalyst & reactants in same phase (e.g., acid hydrolysis of ester).\n- Heterogeneous Catalysis: Catalyst & reactants in different phases (e.g., Haber process - Fe(s) for $\text{N}_2(g) + \text{H}_2(g)$).\n- Enzyme Catalysis: Biological catalysts (proteins), highly specific, optimal T/pH.\n- Autocatalysis: Product acts as catalyst (e.g., $\text{Mn}^{2+}$ in $\text{KMnO}_4$ oxidation of oxalic acid).\n- Promoter: Enhances catalyst activity (e.g., Mo in Haber process).\n- Poison: Decreases catalyst activity (e.g., $\text{H}_2\text{S}$ for Fe catalyst).\n- Activity: Catalyst's ability to increase rate.\n- Selectivity: Catalyst's ability to direct to specific product.

2-Minute Revision

Catalysis is the process of changing a reaction's rate using a catalyst, which remains chemically unchanged. The core mechanism involves the catalyst providing an alternative reaction pathway with a lower activation energy ($E_a$).

This reduction in $E_a$ means more reactant molecules can react, thus accelerating the reaction. Crucially, catalysts do not affect the overall thermodynamics ($\Delta H$, $\Delta G$) or the equilibrium position of a reversible reaction; they only help reach equilibrium faster.

\n\nKey types include homogeneous (same phase, e.g., acid-catalyzed ester hydrolysis), heterogeneous (different phases, e.g., Haber process with Fe catalyst), enzyme (biological, highly specific, sensitive to T/pH), and autocatalysis (product acts as catalyst, e.

g., $\text{Mn}^{2+}$ in $\text{KMnO}_4$ reaction). Catalysts exhibit activity (rate enhancement) and selectivity (product preference). Promoters boost catalyst activity (e.g., Mo in Haber), while poisons reduce it (e.

g., $\text{H}_2\text{S}$ for Fe). Industrial applications like Haber, Contact, and Ostwald processes are vital examples.

5-Minute Revision

Catalysis is the phenomenon where a catalyst alters a reaction's rate without being consumed. The fundamental principle is that catalysts provide a new reaction mechanism with a lower activation energy ($E_a$).

This increases the fraction of molecules with sufficient energy to react, thereby speeding up the reaction. It's critical to remember that catalysts do not change the overall energy difference between reactants and products ($\Delta H$) or the spontaneity ($\Delta G$), nor do they shift the equilibrium position of a reversible reaction; they merely accelerate the rate at which equilibrium is achieved.

\n\nTypes of Catalysis:\n1. Homogeneous: Catalyst and reactants are in the same phase. Example: Acid-catalyzed hydrolysis of an ester, where all components are liquid.\n2. Heterogeneous: Catalyst and reactants are in different phases.

Example: Haber process, where gaseous $\text{N}_2$ and $\text{H}_2$ react on a solid Fe catalyst. This involves adsorption of reactants onto the catalyst surface, reaction, and desorption of products.\n3.

Enzyme: Biological catalysts (proteins) with high specificity and efficiency, operating under specific temperature and pH conditions (e.g., invertase breaking down sucrose).\n4. Autocatalysis: One of the reaction products acts as a catalyst.

Example: The $\text{Mn}^{2+}$ ions produced during the oxidation of oxalic acid by acidified $\text{KMnO}_4$ catalyze the reaction itself.\n\nCharacteristics of Catalysts:\n* Activity: The ability to increase reaction rate, often related to optimal chemisorption strength.

\n* Selectivity: The ability to direct a reaction towards a specific product. Example: $\text{CO} + \text{H}_2$ can yield $\text{CH}_4$, $\text{CH}_3\text{OH}$, or $\text{HCHO}$ depending on the catalyst.

\n* Promoters: Substances that enhance catalyst activity (e.g., Mo for Fe in Haber process).\n* Poisons: Substances that reduce or destroy catalyst activity (e.g., $\text{H}_2\text{S}$ for Fe catalyst).

\n\nIndustrial Examples to Remember:\n* Haber Process: $\text{N}_2 + 3\text{H}_2 \xrightarrow{\text{Fe}, \text{Mo}} 2\text{NH}_3$\n* Contact Process: $2\text{SO}_2 + \text{O}_2 \xrightarrow{\text{V}_2\text{O}_5} 2\text{SO}_3$\n* Ostwald Process: $4\text{NH}_3 + 5\text{O}_2 \xrightarrow{\text{Pt-Rh gauze}} 4\text{NO} + 6\text{H}_2\text{O}$\n* Hydrogenation of Vegetable Oils: Unsaturated oil + $\text{H}_2 \xrightarrow{\text{Ni}}$ Saturated fat\n\nFocus on understanding these concepts and memorizing the key examples and their associated catalysts for NEET.

Prelims Revision Notes

1
Definition: — A catalyst is a substance that alters the rate of a chemical reaction without being consumed. It is regenerated at the end of the reaction.\n2. Mechanism: Catalysts provide an alternative reaction pathway with a lower activation energy ($E_a$). This increases the number of effective collisions, thus increasing the reaction rate.\n3. No Effect on Thermodynamics: Catalysts do NOT change $\Delta H$ (enthalpy change), $\Delta G$ (Gibbs free energy change), or the equilibrium constant ($K_{eq}$) of a reaction. They only help reach equilibrium faster.\n4. Types of Catalysis:\n * Homogeneous: Catalyst and reactants are in the same phase (e.g., liquid-liquid, gas-gas). Example: Acid-catalyzed hydrolysis of esters (all liquid); Lead chamber process for $\text{SO}_3$ (all gas, $\text{NO}$ catalyst).\n * Heterogeneous: Catalyst and reactants are in different phases (e.g., solid catalyst, gaseous reactants). Example: Haber process (Fe(s) for $\text{N}_2(g) + \text{H}_2(g)$); Contact process ($\text{V}_2\text{O}_5(s)$ for $\text{SO}_2(g) + \text{O}_2(g)$); Hydrogenation of oils (Ni(s) for liquid oil + $\text{H}_2(g)$).\n * Enzyme: Biological catalysts (mostly proteins). Highly specific, very efficient, sensitive to temperature and pH (optimal range). Example: Urease, Invertase.\n * Autocatalysis: One of the products of the reaction acts as a catalyst. Example: Oxidation of oxalic acid by acidified $\text{KMnO}_4$, where $\text{Mn}^{2+}$ (product) catalyzes the reaction.\n5. Characteristics of Catalysts:\n * Activity: Ability to increase reaction rate. Related to optimal chemisorption strength.\n * Selectivity: Ability to direct reaction to a specific product. Example: $\text{CO} + \text{H}_2$ yields different products with different catalysts (Ni for $\text{CH}_4$, $\text{CuO/ZnO-Cr}_2\text{O}_3$ for $\text{CH}_3\text{OH}$).\n * Promoters: Substances that enhance catalyst activity (e.g., Mo in Haber process).\n * Poisons: Substances that decrease or destroy catalyst activity (e.g., $\text{H}_2\text{S}$ for Fe catalyst, CO for Pt catalyst).\n6. Industrial Processes & Catalysts:\n * Haber Process ($\text{NH}_3$): Fe (catalyst), Mo (promoter).\n * Contact Process ($\text{H}_2\text{SO}_4$): $\text{V}_2\text{O}_5$.\n * Ostwald Process ($\text{HNO}_3$): Pt-Rh gauze.\n * Hydrogenation of Vegetable Oils: Ni.\n * Catalytic Converters: Pt, Pd, Rh.

Vyyuha Quick Recall

Catalysts Alter Rates, Energy Lowered, No Equilibrium Shift. (CARE LNES)\n* Catalysts: are not consumed.\n* Alter Rates: usually increase reaction rate.\n* Energy Lowered: by providing a new pathway with lower Activation Energy ($E_a$).\n* No Equilibrium Shift: equilibrium constant and position remain unchanged.