Presentation on theme: "Reaction Rate How Fast Does the Reaction Go Collision Theory Chemists believe that all chemical change (rearrangement of matter) occurs due to the collision."— Presentation transcript:
Things that affect rate 2. Concentration -More concentrated closer together the molecules. -Collide more often. -Faster reaction.
Things that Effect Rate 3. Nature of reactants a. Reactions are rapid at room temperature if no bonds are required Ionic reactions: Pb 2+ + SO 4 2- → PbSO 4
b. Reactions are slow at room temperature when several bonds in the reacting substances must be broken Molecular reactions C 2 H 5 OH + 3 O 2 2CO 2 + 3H 2 O
4. Surface area -Molecules can only collide at the surface. Smaller particles bigger surface area. Smaller particles faster reaction.
5. a)Catalysts- substances that speed up a reaction without being used up.(enzyme). -Speeds up reaction by giving the reaction a new path. -The new path has a lower activation energy. -More molecules have this energy. -The reaction goes faster. b) Inhibitor- a substance that blocks a catalyst (raises the activation energy).
Catalysts Increase the Number of Effective Collisions
Reaction Mechanism Elementary reaction- a reaction that happens in a single step. Reaction mechanism is a description of how the reaction really happens. It is a series of elementary reactions. The product of an elementary reaction is an intermediate. An intermediate is a product that immediately gets used in the next reaction.
Mechanisms and rates There is an activation energy for each elementary step. Slowest step (rate determining) must have the highest activation energy.
A chemical example of a Reaction Mechanism H 2 (g)+I 2 (g) → 2HI (g) This reaction is very slow at room temperature but if the system is exposed to sunlight ( source of UV light ) the reaction proceeds rapidly.