2. RATE OF REACTION
• Rate of reaction is the speed of reaction
• The speed of different chemical reactions varies hugely.
• Some reactions are very fast and others are very slow.
• The rate of an enzyme-catalyzed reaction increases with an increase
in the concentration of an enzyme.
• At low temperatures, an increase in temperature increases the rate of
an enzyme-catalyzed reaction.
• At higher temperatures, the protein is denatured, and the rate of the
reaction dramatically decreases
3. • Factors Affecting Reaction Rate
• The concentration of reactants: A higher concentration of reactants
leads to more collisions per unit time, which leads to an increased
reaction rate
• Temperature: Usually, an increase in temperature is accompanied by
an increase in the reaction rate.
• The presence of catalysts: Catalysts (such as enzymes) lower the
activation energy of a chemical reaction and increase the rate of a
chemical reaction without being consumed in the process.
• The physical state of reactants: Reactants in the same phase may
come into contact via thermal action, but surface area and agitation
affect reactions between reactants in different phases.
• Pressure: For reactions involving gases, raising pressure increases the
collisions between reactants, increasing the reaction rate.
4. • Zero-Order Reactions
• Zero-order reactions (where order = 0) have a constant rate. The rate
of a zero-order reaction is constant and independent of the
concentration of reactants. This rate is independent of the
concentration of the reactants. The rate law is:
• rate = k, with k having the units of M/sec.
• A few substances are eliminated by zero-order elimination kinetics,
because their elimination process is saturated.
• Examples are Ethanol, Phenytoin, Salicylates, Cisplatin, Fluoxetin,
Omeprazol.
5. • PSEUDO–ORDER REACTIONS
• A reaction in which one of the reactants is present in a large excess
shows an order different from the actual order.
• The experimental order which is not the actual one is referred to as
the pseudo order.
• Since for elementary reactions molecularity and order are identical,
pseudo-order reactions may also be called pseudo molecular
reactions
7. • FIRST ORDER REACTIONS
• An order of chemical reaction in which the rate of the reaction
depends on the concentration of only one reactant, and is
proportional to the amount of the reactant.
8. • SECOND ORDER REACTIONS
• second-order kinetics. A term describing the reaction rate of a
chemical reaction in which the rate is proportional to the product of
the concentrations (in moles) of two of the reactants (also called
bimolecular kinetics), or to the square of the molar concentration of
the reactant if there is only one.
9. • THIRD ORDER REACTIONS
• A third-order reaction is a chemical reaction where the rate of
reaction is proportional to the concentration of each reacting
molecules. In this reaction, the rate is usually determined by the
variation of three concentration terms.
• TURNOVER
• In enzymology, turnover number (also termed kcat) is defined as the
maximum number of molecules of substrate that an enzyme can
convert to product per catalytic site per unit time and can be
calculated as follows: kcat = Vmax/[E]T . For example, carbonic
anhydrase has a turnover number of 400,000 to 600,000 s-1, which
means that each carbonic anhydrase molecule can produce up to
600,000 molecules of product (CO2) per second.
