Chemical Kinetics: Reaction Rates and Collision Theory

Vocabulary flashcards covering reaction rate definitions, collision theory components, factors influencing rates (concentration, temperature, catalysts), and energy diagrams.

Rate of reaction (reactants)

The rate expressed as negative change in reactants over change in time ($-\frac{\Delta r}{\Delta t}$), mathematically inverted with a negative sign to keep the measured rate as a positive value since reactant amounts decrease.

Rate of reaction (products)

The rate expressed as the change in product amount divided by the elapsed time ($\frac{\Delta p}{\Delta t}$), yielding an inherently positive value because product amounts increase over the course of a reaction.

Collision theory

A theoretical model explaining that for a chemical reaction to occur, reactant molecules must physically collide, possess sufficient energy to break existing chemical bonds, and collide with the proper orientation.

Activation energy ($E_a$)

The minimum energy threshold required during a molecular collision to snap existing bonds apart and initiate a reaction, represented as an energetic hill on a reaction diagram.

Molecular orientation

The spatial alignment of colliding molecules during an impact, which determines whether reacting atoms are positioned correctly to break old bonds and form new ones.

Collision frequency

The rate at which particles collide in a given space, which increases when reactant concentration or amount is increased, leading to a higher reaction rate.

Kinetic energy in reactions

The energy of motion described by $\frac{1}{2}mv^2$, which increases as temperature increases, causing molecules to travel faster and collide hard enough to overcome the activation energy.

Catalyst

A substance introduced to a reaction mixture that accelerates the reaction rate by assisting with molecular orientation and lowering the activation energy required for a successful collision.

Enzyme

A biological catalyst that accelerates biochemical reactions by binding substrates (such as glucose) in a specific orientation and stretching chemical bonds to reduce the energy needed for reaction.

Energy diagram (reaction profile)

A graph plotting energy versus reaction coordinate or progress, illustrating the relative potential energies of reactants and products, activation energy, and the net enthalpy change ($\Delta H$).

Endothermic reaction

A reaction where the products are higher in energy than the reactants, requiring an input of energy and resulting in a positive value for $\Delta H$.

Exothermic reaction

A reaction where the products are lower in energy than the reactants, releasing energy and resulting in a negative value for $\Delta H$.

$\Delta H$ (Enthalpy change of reaction)

The difference in energy between products and reactants ($\text{products} - \text{reactants}$) shown on an energy diagram, which is positive for endothermic processes and negative for exothermic processes.