Lesson 10 - Factors Affecting Reaction Rate Flashcards
What are the factors affecting reaction rate?
Nature of reactants, Concentration, Temperature, Pressures of gases, Surface area of solids, Catalysts
Why do reactions between ions in solution tend to have rapid reaction rates?
No bonds need to be broken, positive and negative ions attract each other
Why do reaction between acids and bases (neutralization) tend to have rapid reaction rates?
Acids and bases are oppositely charged after ionization and thus attract each other
Why do reaction between molecules tend to have relatively slow reaction rates?
Existing bonds must be broken, large and strong bonds are especially slow
How does concentration affect reaction rate?
The greater the concentration of reactants, the larger number of particles in a given space, causing a larger number of collisions. Kinetic and activation energy remain constant, but the number of effective collisions will increase based on probability alone.
Why will reaction rate decrease as the reaction progresses?
The reaction rate will decrease as the concentration of reactants decrease and concentration of products increase. Reactants are more likely to collide with products than other reactants.
How does temperature affect reaction rate?
Increasing the temperature increases the kinetic energy of the reactants, causing more frequent collisions, causing more effective collisions.
Increasing the temperature means more particles will have sufficient activation energy.
Increase in energy does NOT change the reaction pathway or the activation energy
How does pressure of gases affect reaction rate?
Increasing pressure increases the number of collisions, and thus increases the number of successful collisions.
How can pressure be increased?
Pressure can be increased by decreasing volume. Pressure can also be increased by increasing the number of particles given in a given volume.
How does surface area affect reaction rate?
The greater the surface area, the greater the number of collisions and the greater the chance of successful (effective) collisions.
Smaller pieces of reactants have a greater amount of exposed surface area available for collisions compared with larger pieces that have the same total mass.
Catalysts
Substances that increase the rate of a chemical reaction without being consumed y the reaction. It lowers the activation energy.
How do catalysts affect reaction rate?
Once activation energy is decreased, a greater percentage of particles will have enough kinetic energy to collide successfully.
Catalysts are not consumed by a reaction but …
Catalysts are not consumed but can be changed. However, they will always return to their original condition by the completion of the overall reaction.
What are the 2 types of catalysts and briefly explain
- Homogenous catalysts: when reactant, products and catalysts are all in the same state-usually gaseous phase or solution
- Heterogeneous catalysts: when the catalyst is present in a different phase of matter than the products and reactants.
Steps of heterogeneous catalysis
- Adsorption of reactants: the reactants (substrate) attach to and form a thin layer on the surface (active site) of the catalyst
- Diffusion of the reactants along the active site
- Reaction at an active site to form an adsorbed product
- Desorption to release the catalyst from the product
