Reaction Rates Chapter 17

What is Rate? The average rate of a process is a measure of the change of the quantity divided by the change in time. The rate can be expressed as the rate of disappearance of either the reactants or the rate of appearance of either of the products.

Factors That Affect Reaction Rate Remember, that in order for a reaction to occur the particles have to collide. There are four factors that affect reaction rate: Surface Area Concentration Temperature Presence of catalysts/inhibitors

Surface Area If the reactants have a larger surface area, the reaction can occur on the surface of the reactant, making the reaction occur faster.

Concentration Increasing the concentration of one or more reactants puts more particles of the reactants in the same space, thereby increasing the frequency of collisions.

Temperature Increasing the temperature of a reaction increases the frequency of collisions between particles, which allows more opportunities for rxn.

Catalyst A catalyst is a substance that increases the rate of a chemical rxn without being consumed. A catalyst reduces the activation energy needed for the rxn because the particles can interact with each other on the surface. An inhibitor is a compound that slows down, or inhibits, a chemical rxn.

Practice Use the factors discussed to account for the following. When two gases react, compressing the gases generally increases the rate of rxn. The rate of gaseous rxns can also be increased by pumping more gas into the rxn container. A pile of kindling consists of small sticks, wood shavings and scraps of paper and burns quickly, giving off enough heat to begin a fire in a pile of large logs. The logs burn much slower than kindling.