Haber Process ($\text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3$): Iron catalyst with $\text{K}_2\text{O}/\text{Al}_2\text{O}_3$ promoters lowers $E_a$, dramatically increasing the rate at industrially manageable temperatures (~450 °C, 200 atm). Without the catalyst the reaction is practically too slow at any accessible temperature. Kinetics determines the optimal operating conditions — high pressure increases rate and shifts equilibrium toward product; temperature is a compromise between rate (needs heat) and equilibrium yield (exothermic, favoured at low T).

Contact Process for $\text{H}_2\text{SO}_4$ ($\text{SO}_2 \rightarrow \text{SO}_3$): $\text{V}_2\text{O}_5$ catalyst. The catalyst undergoes a cyclic mechanism: $\text{V}^{5+}$ oxidises $\text{SO}_2$ to $\text{SO}_3$ and is reduced to $\text{V}^{4+}$, then re-oxidised by $\text{O}_2$. This is an example of a homogeneous intermediate mechanism — the catalyst participates in the reaction but is regenerated.

Radioactive Decay (first order): $^{238}\text{U} \rightarrow ^{234}\text{Th} + ^4\text{He}$; $t_{1/2} = 4.5 \times 10^9$ years. Carbon-14 dating exploits $t_{1/2} = 5730$ years for $^{14}\text{C}$ to determine the age of organic material. The first-order nature (concentration-independent half-life) is what makes the dating reliable.

$\text{H}_2\text{O}_2$ Decomposition: $2\text{H}_2\text{O}_2 \rightarrow 2\text{H}_2\text{O} + \text{O}_2$ — first-order in dilute solution. Used in rocket propulsion (high-test peroxide) and as a bleaching agent. Catalysed by $\text{MnO}_2$, $\text{KI}$, or enzymes (catalase in blood).

Enzyme Kinetics (Michaelis–Menten): At low substrate concentration, enzyme reactions follow first-order kinetics; at saturation (enzyme fully occupied), they become zero order in substrate — a direct application of surface-saturation kinetics.

Ozone Depletion: $\text{CFCs} \xrightarrow{h\nu} \text{Cl}^{\bullet}$; then $\text{Cl}^{\bullet} + \text{O}_3 \rightarrow \text{ClO}^{\bullet} + \text{O}_2$. Cl acts as a homogeneous catalyst — it is consumed in one step but regenerated in another, lowering the activation energy for $\text{O}_3$ decomposition. Kinetics here determines the stratospheric lifetime of ozone.

Food Preservation: Low temperature slows spoilage reactions (microbial metabolism, lipid oxidation) because $k = Ae^{-E_a/RT}$ — reducing $T$ reduces $k$ exponentially. Refrigeration at 4 °C vs 25 °C slows reactions by a factor of roughly $2^{2.1} \approx 4$ based on the temperature coefficient.

Catalytic Converters: Pt/Pd/Rh catalyst converts $\text{CO}$, unburnt hydrocarbons, and $\text{NO}_x$ in exhaust. Zero-order behaviour can occur at high exhaust concentrations when catalyst surface is saturated — explaining why efficiency drops under rich fuel conditions.