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Factors Affecting Reaction Rates
• presence/absence of a catalyst.
• surface area (particle size)
• concentration or pressure of a reactant
• temperature
• 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
+
EA
-∆H
AC
Effect of Particle Size (surface area)
Rate of reaction increases with increased surface area (crushing, grinding) .
More particles involved, more frequent collisions.
Effect of Concentration
Rate of reaction increases with increased concentration (mol/L) of particles.
More particles with activation energy - more chances of a successful collision.
Effect of PressureOnly affects reaction rates of gaseous reactions.
Rate of reaction increases with decreased volume of the container - mimics higher [ ].
Closer particles – more chance of collisions.
Effects of a Temperature ChangeRate of reaction increases with increased temperature.
More KE per particle – more frequent collisions and more EA.
10°C increase in temp usually doubles reaction rate.
Effect of the Nature of Reactants
1. Comparing reactions with similar compounds:
Less bonds to break, faster the reaction.
2 C8H18(g) + 25 O2(g) → 16 CO2(g) + 18 H2O(g)
2 NO(g) + O2(g) → 2 NO2(g)
Covalent bonds takes longer to break than aqueous.
(aq) are already separated into ions, so are instantaneous.
KNO3(aq) + NaI(aq) → KI(aq) + 2 NaNO3(aq)
2. Comparing reactions with similar bond numbers:
H2(g) + I2(g) → 2 HI(g)
KNO3(aq) + NaI(aq)→ KI(aq) + NaNO3(aq)
K+
Na+
I-
NO3-
3. Comparing similar compounds and similar bond numbers:
(g) faster > (l) > (s)
• Stronger IMF to overcome• Less KE per particle• Less collisions • Less Surface area
Effect of Catalysts
A catalyst speeds up or starts a reaction by lowering the activation energy.
An inhibitor is the opposite of a catalyst.
Enzymes are known as biological catalysts.
• Does not alter products or ΔH.• Not involved in the overall chemical reaction• Appears unchanged.
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