Chemical Kinetics: Factors Affecting Rate of Reactions

• Factors affecting the rate of reactions:
  • Nature of Reactants
  • Concentration of Reactants
  • Temperature
  • Pressure
  • Catalysts

Nature of Reactants

• Different reactants have different reaction rates.
• Reactants in the same state usually have similar rates.
• For example:
  • Solid-solid reactions tend to be slow.
  • Gas-gas reactions tend to be fast.

Concentration of Reactants

• Rate of reaction is directly proportional to the concentration of reactants.
• Higher concentration leads to more frequent collisions and faster reaction rates.
• For example:
  • Increasing the concentration of a solution increases the rate of reaction.

Temperature

• Increasing temperature increases the average kinetic energy of particles.
• Higher kinetic energy means higher chances of successful collisions.
• The rate of reaction generally doubles for every 10°C increase in temperature.
• For example:
  • The reaction between hydrogen and oxygen is faster at higher temperatures.

Pressure

• Only applicable to gas-phase reactions.
• Increasing the pressure decreases the volume of the gases.
• Smaller volumes make collisions more frequent, leading to higher reaction rates.
• For example:
  • The reaction between gases in a confined space occurs faster at higher pressures.

Catalysts

• Catalysts are substances that speed up the reaction without being consumed.
• They provide an alternative reaction pathway with lower activation energy.
• Catalysts increase the rate of reaction without being permanently changed.
• For example:
  • Enzymes are biological catalysts that speed up specific chemical reactions.

End of slides for Chemical Kinetics: Factors Affecting Rate of Reactions

Chemical Kinetics: Factors Affecting Rate of Reactions

Nature of Reactants

• Different reactants have different reaction rates.
• Reactants in the same state usually have similar rates.
• For example:
  • Solid-solid reactions tend to be slow.
  • Gas-gas reactions tend to be fast.

Concentration of Reactants

• Rate of reaction is directly proportional to the concentration of reactants.
• Higher concentration leads to more frequent collisions and faster reaction rates.
• For example:
  • Increasing the concentration of a solution increases the rate of reaction.

Temperature

• Increasing temperature increases the average kinetic energy of particles.
• Higher kinetic energy means higher chances of successful collisions.
• The rate of reaction generally doubles for every 10°C increase in temperature.
• For example:
  • The reaction between hydrogen and oxygen is faster at higher temperatures.

Pressure

• Only applicable to gas-phase reactions.
• Increasing the pressure decreases the volume of the gases.
• Smaller volumes make collisions more frequent, leading to higher reaction rates.
• For example:
  • The reaction between gases in a confined space occurs faster at higher pressures.

Catalysts

• Catalysts are substances that speed up the reaction without being consumed.
• They provide an alternative reaction pathway with lower activation energy.
• Catalysts increase the rate of reaction without being permanently changed.
• For example:
  • Enzymes are biological catalysts that speed up specific chemical reactions.

Reaction Rate

• The reaction rate is defined as the change in concentration of reactants or products per unit of time.
• It can be represented as:
  • Rate = Δ[C]/Δt for reactants (negative sign indicates consumption)
  • Rate = Δ[D]/Δt for products (positive sign indicates formation)
• The unit of reaction rate depends on the order of the reaction.

Rate Law

• The rate law represents the relationship between the rate of reaction and the concentrations of reactants.
• It can be expressed as:
  • Rate = k[A]^m[B]^n
  • ‘k’ is the rate constant, and ’m’ and ’n’ are the reaction orders with respect to reactants A and B, respectively.
  • The overall reaction order is m + n.

Rate Constants

• The rate constant (k) is unique for each reaction at a specific temperature.
• It depends on the nature of the reaction, reactants, and temperature.
• The value of k can be determined through experimental methods.
• The units of k depend on the overall reaction order.

Reaction Order

• The reaction order represents the relationship between the concentration of a reactant and the rate of reaction.
• It can be determined experimentally by varying the concentration of a single reactant and observing the effect on the reaction rate.
• The sum of the reaction orders for all reactants gives the overall reaction order.

Rate Determining Step

• In a multi-step reaction, the slowest step is known as the rate-determining step.
• The rate of the overall reaction is determined by the rate of this slowest step.
• The rate equation is derived from the elementary steps involved in the reaction.
• The rate-determining step has the highest activation energy.

End of slides for Chemical Kinetics - Factors Affecting Rate of Reactions

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