Reaction Rates

What does rate mean? measure of the speed of any change that occurs within an interval of time time can range from microseconds (explosions) to centuries (plants to coal) in chemistry…reaction rate is usually expressed as the amount of the reactant changes per unit time 3 moles/year 5 grams/second

Collision Theory http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/collis11.swf only a small fraction of collisions produce a chemical reation “effective collisions” have enough kinetic energy and the collide at the correct angle need enough KE to assemble new compounds break the bonds of existing compounds

Activation Energy http://www.youtube.com/watch?v=VbIaK6PLrRM minimum energy that colliding particles must have in order to react an activated complex is an unstable compound that forms momentarily at the peak of the “barrier” typically about 10-13 seconds both reactants reform and new products form also referred to as the transition state

Activation Energy

Factors Affecting Reaction Rate The rate of a chemical reaction depends on: temperature increasing temp. increases the frequency of collisions AND the KE necessary to overcome the activation energy barrier http://www.absorblearning.com/media/item.action;jsessionid=42FA5DD70632A65FCDF283D4A8A8688E?quick=w2

http://www. absorblearning. com/media/attachment. action http://www.absorblearning.com/media/attachment.action?quick=vy&att=2290 concentration increasing the number of particles in a given volume increases the rate a which reactions occur

particle size surface area affects the reaction rate smaller particles have a greater ratio of surface area (x2) to volume (x3) this increases the amount of reactant exposed for reactions http://www.absorblearning.com/media/item.action;jsessionid=7ED974B68776F95D4EAE0585F73F61B7?quick=vw An iron bar is held in a flame and nothing happens. Iron powder is then blown into the flame and ignites

presence of a catalyst a substance that increases the rate of a reaction without being used up during the reaction

inibitors interfere with the action of the catalyst