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Factors Affecting Reaction Rates

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.

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Factors Affecting Reaction Rates

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

  2. 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

  3. 2 H2 + O2 → 2 H2O AC EA -∆H + Potential Energy Kinetic Energy Kinetic Energy Kinetic Energy Kinetic Energy

  4. Effect of Particle Size (surface area) Rate of reaction increases with increased surface area(crushing, grinding) . Moreparticlesinvolved, morefrequentcollisions, higherchancesof successful collisions.

  5. Effect of Concentration Rate of reaction increases with increased concentration (mol/L) of particles. Moreparticlesinvolved, morefrequentcollisions, higherchancesof successful collisions.

  6. Effect of Pressure Only affects reaction rates of gaseous reactions. Rate of reaction increases with decreased volume of the container - mimics higher [ ]. Closerparticles, morefrequent collisions, higherchancesof successful collisions.

  7. Effects of a Temperature Change Rate of reaction increases with increased temperature. Morekinetic energy, moreparticles with EA, higherchancesof successful collisions.

  8. 10°C increase in temp usually doubles reaction rate.

  9. 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)

  10. 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)

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

  12. 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

  13. Effect of Catalysts • A catalyst speeds up areactionby 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.

  14. Catalyst: Lower EA Activation Energy

  15. 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....

  16. 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

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