Factors Affecting Reaction Rates temperature concentration or pressure of a reactant surface area (particle size) presence/absence of a catalyst. nature of the reactants

Quantitatively identify factors that affect the rate of a chemical reaction. Include: nature of reactants, surface area, concentration, pressure, volume, temperature, and catalyst. Describe the relationship between these factors and the relative rate using the Collision Theory. Additional KEY Terms

+ 2 H2 + O2 → 2 H2O AC EA -∆H Kinetic Energy Kinetic Energy Potential

Effect of Particle Size (surface area) Rate of reaction increases with increased surface area (crushing, grinding) . More particles involved, more frequent collisions, higher chances of successful collisions.

Effect of Concentration Rate of reaction increases with increased concentration (mol/L) of particles. More particles involved, more frequent collisions, higher chances of successful collisions.

Effect of Pressure Only affects reaction rates of gaseous reactions. Rate of reaction increases with decreased volume of the container - mimics higher [ ]. Closer particles, more frequent collisions, higher chances of successful collisions.

Effects of a Temperature Change Rate of reaction increases with increased temperature. More kinetic energy, more particles with EA, higher chances of successful collisions.

10°C increase in temp usually doubles reaction rate.

Less bonds to break: faster the reaction. Effect of the Nature of Reactants 1. Comparing reactions with similar compounds Less bonds to break: faster the reaction. 2 NO(g) + O2(g) → 2 NO2(g) 2 C8H18(g) + 25 O2(g) → 16 CO2(g) + 18 H2O(g)

KNO3(aq) + NaI(aq) → KI(aq) + 2 NaNO3(aq) 2. Comparing reactions with similar bond numbers Covalent takes longer to break than aqueous ionic (aq): already separated into ions, so instantaneous reaction. H2(g) + I2(g) → 2 HI(g) KNO3(aq) + NaI(aq) → KI(aq) + 2 NaNO3(aq)

Na+ K+ I- NO3- KNO3(aq) + NaI(aq)→ KI(aq) + NaNO3(aq) Ionic compounds in solution separate into ions – no “bonds” to break. KNO3(aq) + NaI(aq)→ KI(aq) + NaNO3(aq) Na+ K+ I- NO3-

(g) faster > (l) > (s) 3. Comparing similar compounds and similar bond numbers (g) faster > (l) > (s) Less Intermolecular forces to overcome More KE per particle More surface area More COLLISIONS

Effect of Catalysts A catalyst speeds up a reaction by lowering EA Does not alter products or ΔH. Appears unchanged. Often not shown in the overall chemical reaction Enzymes are known as biological catalysts. An inhibitor is the opposite of a catalyst.

Activation Energy Catalyst: Lower EA

Things that increase reaction rate: increased surface area increased concentration increased pressure increased temperature fewer bonds, aqueous or gas states catalyst To decrease reaction rate - do the opposite....

CAN YOU / HAVE YOU? Quantitatively identify factors that affect the rate of a chemical reaction. Include: nature of reactants, surface area, concentration, pressure, volume, temperature, and catalyst. Describe the relationship between these factors and the relative rate using the Collision Theory. Additional KEY Terms