CHEM 112 FACTORS THAT AFFECT REACTION RATES ntroduction Rates of reaction are no
ID: 476431 • Letter: C
Question
CHEM 112 FACTORS THAT AFFECT REACTION RATES ntroduction Rates of reaction are normally defined in terms of change of concentration of either a reactant or a product per unit time. These reaction rates may simply be explained by collision theory. For almost all reactions, species must collide with enough energy and the correct orientation so as to react. The required energies and orientations are specific to the reaction in question. The energy barrier to reaction is called the activation energy. The activation eneray is related to the rate constant of the reaction, which in tum is related to the rate of the reaction by the rate law Equation 2. The Antenius equation relates requency factor A.the activation energy. E, the gas constant R (8314 Mmol-K) and the absolute the rate constant k to the temperature T Equation 3. The frequency factor is related to the frequency ofcollisions and the orientation of reacting A B C+D+ rate k[A] TB] From a mathematical inspection of the Arrhenius equation it is seen that, as the temperature of the reaction is changed. the rate constant (and in fact the rate) of the reaction should change. The general rule of thumb is that every 10 K rise in the temperature will bring about a doubling (or up to a tripling) change in the reaction rate (an equivalent lowering of Also, as the nature of the reaction changes. that is, the result in the of the reaction rate). the temperature wi activation energy changes, the rate changes correspondingly. As E, gets larger, the rate slows exponentially while lowering the energy barrier results in the reaction speeding up exponentially. These effects are seen in reactions by changing the nature of the reactants (e.g..the oxidation of different metals by aqueous acid) and by introducing catalysts that lower the activation energy of the reaction being studied. Even with the activation energy and temperature constant,there are other factors that affect reaction rates. These are almost entirely due to changes in collision frequencies of the reacting species. the collision frequency changes rate of the reaction will accordingly. Changing the of those species in the law or changing the surface area a in a heterogeneous reaction can change collision frequency reaction. Next week. we will Today we will qualitatively investigate a few of these that affect rates of quantitatively derive the rate law for the decomposition of hydrogen peroxide (part D). Procedure Materials: 020 M KI, o.10 M (NH)as,oi (ammonium peroxydisulfate).00020 M Nazs,o (sodium thiosulfate). starch solution 6 M solutions of HCI HINO, NH, HC Hyo. (acetic acid). and H,PO, 39 Hzo, 020 M Mncia Fe (nail, granular and powdered).zn (20 mesh). and Al strips (1" x 1/4") Effect of Temperature To a beaker add 10.0 mL of 0.0020 M Nazs,o,. To this add 6 drops of starch solution and 100 ml of 020 M KI. Mix thoroughly. To another beaker add 100 mL of 0.10 M (NH Szo. Record the temperature of both solutions (they should be the same). Quickly pour the ammonium peroxydisulfate solution into the first beaker. Record the time it takes for the solution to turm blue (triiodide.starch complex). Repeat this procedure at approximately 10 "Cand 35 "C. Reaction Temperature Beaker 1 Room Temperature 6 drops ml 100 mL 50 mlL 0.0 mL About 6 drops 100 mL 100 mL 50 ml 0.0 mL. 3 About 35°C 6 drops 100 mL 100 mL 50 mL 00 mL.Explanation / Answer
1. As the temperature of a reaction increase rate constant of reaction increase and hence the rate also increase.
2. In terms of collision theory
As temperature increases energy of each reactants increase so the number of molecules crossing activation energy barrier increase and hence more reactants molecules have effective collision so number of product molecules increase and hence rate increases.