Reaction Kinetics

• Chemistry focuses on kinetics and equilibrium.

Kinetics

• Collision theory states that reactant particles must collide with appropriate orientation and sufficient energy for a reaction to occur.
• Activation energy is the minimum energy required for reactant particles to react upon collision.
• The rate of reaction is the change in concentration of reactants or products over time.
• Reaction rate can be studied by monitoring mass loss, gas volume, or changes in pressure or color.

Factors Increasing Reaction Rate

• Decreasing particle size increases surface area, enabling more frequent collisions.
• Increased concentration means molecules are closer, leading to more frequent collisions.
• Increased pressure forces molecules closer, promoting more frequent collisions.
• Higher temperature raises the kinetic energy of molecules, increasing the proportion with energy exceeding activation energy for successful collisions.
• Catalysts speed up reactions by providing alternative pathways with lower activation energy, remaining unchanged themselves.
• Initially, reactions proceed at the fastest rate with the highest reactant concentration, indicated by a steeper slope on a graph.
• As reactions progress and reactant concentrations decrease, the rate slows due to less frequent collisions, resulting in a less steep slope.
• The reaction stops when the curve flattens because reactants have been used up.

Maxwell-Boltzmann Distribution Curves

• Illustrate the energy distribution among gas particles.
• The total area under the curve represents the number of molecules, which remains constant regardless of temperature.
• Increasing the temperature shifts the curve, maintaining the area but changing the distribution.
• If you remove half the molecules the shape stays the same.
• Adding a catalyst results in the curve being the same shape.
• By Reducing the volume, the curve stays the same shape.
• Reducing the temperature the peak moves higher and the the left.
• By adding an inert gas, the curve stays the same shape.

Equilibrium

• Dynamic equilibrium exists when reactant and product concentrations remain constant, and forward and reverse reaction rates are equal, achievable only in a closed system.
• Kc is the equilibrium constant at a specific time and fixed temperature.
• Le Chatelier's principle predicts how a reaction at equilibrium responds to changes by opposing the effect of the disturbance.

Catalyst effect on equilibrium

• Adding a catalyst does not shift equilibrium but increases forward and reverse reaction rates equally.

Pressure effect on Equilibrium

• The effect of pressure (or volume) depends on gas moles.
• The equilibrium shifts to the side with less gas moles when pressure increases (or volume decreases).
• The equilibrium shifts to the side with more gas moles when pressure decreases (or volume increases).

Temperature effect on equilibrium

• For endothermic reactions, equilibrium shifts toward the products with increasing temperature and the reactants with decreasing temperature.
• For exothermic reactions, conversely, equilibrium shifts toward reactants with increasing temperature and products with decreasing temperature.

Concentration effect on Equilibrium

• Increasing reactant concentration shifts equilibrium to the right, favoring product formation, while increasing product concentration shifts it left, favoring reactant formation.
• Decreasing reactant concentration shifts equilibrium to the left, while decreasing product concentration shifts it right.