Chapter 18: Equilibrium

Collision Theory Rate: Change over time Rate of chemical change (reaction rate) is amount of reactant changing over time. For atoms, ions, and molecules to react to form products, they must collide with one another with the proper amount of kinetic energy and activation energy.

Activated Complex Also called Transition State Lasts for a VERY short time The unstable arrangement of atoms that forms momentarily at the peak of the AC barrier. Forms only if the colliding particles have sufficient energy and if the atoms are oriented properly.

Factors Affecting Reaction Rates Temperature Concentration Particle Size Catalysts

Temperature The faster the particles move, the more they collide, the higher the reaction rate.

Concentration The more particles you have, the more they collide, the faster the rate.

Particle Size Function of Surface Area Surface area is defined as the parts of the reactant that is available for reaction. The smaller the particle size, the larger the surface area. An increase in surface area increases the amount of the reactant exposed for the reaction, which increases collisions, which increases the reaction rate.

Catalysts Increase the rate of reactions by lowering the activated complex. NOT affected or involved in the reaction, simply help it along. Does not change PER, PEP, or enthalpy. INHIBITOR: interferes with the action of a catalyst.

Pressure ONLY AFFECTS GASES!!! – If we increase the pressure on a gas, we push them closer together, therefore more collisions, therefore the reaction rate increases. ONLY AFFECTS GASES!!!

Equilibrium Reactions can go forward OR reverse. Reactions can go forward and reverse at the same time, at different rates, or the same rate. When the forward reaction and the reverse reaction is occurring at the same rate, it is said to be in EQUILIBRIUM.

Equilibrium Constant An expression of equilibrium mathematically. Equilibrium is an expression of the concentration of the products vs. the concentration of the reactants.