2.8.2 – Factors that influence the rate of reaction e. demonstrate an understanding of the role of catalysts in providing alternative reaction routes of lower activation energy and draw the reaction profile of a catalysed reaction including the energy level of the intermediate formed with the catalyst f. carry out simple experiments to demonstrate the factors that influence the rate of chemical reactions, eg the decomposition of hydrogen peroxide. Connector: Draw and fully label the reaction profile for an endothermic reaction Sketch and fully label Maxwell-Boltzmann distribution curves to show the effect of an increase in temperature on the energy of the particles in a gaseous reaction Explain how a catalyst affects the rate of a reaction Crowe2009

Catalysts A catalyst is a substance that speeds up a chemical reaction. A catalyst is not used up in the reaction it catalyses, and so can be used over and over again. "A catalyst provides an alternative route for the reaction with a lower activation energy."

More about catalysts .1 "A catalyst provides an alternative route for the reaction with a lower activation energy." Ea1 is the activation energy leading to the formation of an intermediate complex. Ea2 is the activation energy for the change of the intermediate complex into products. Ea3 is the activation energy of the uncatalysed reaction.

More about catalysts .2 The catalyst combines with one of the reactants to form a intermediate known as a reactant-catalyst complex (an activated complex) which then reacts with another reactant to form the products – hence two humps. reactant-catalyst complex

More about catalysts .3 A + B C + D A + A- A- + B C + D + Ea3 Ea1 Ea2 reactant-catalyst complex

Measuring reaction rates Marble chips Glass tube Gas syringe Hydrochloric acid Mg HCl Research these other methods you need to know about: titrimetric analysis colorimetric analysis conductimetric analysis

Iodine clock - demo http://www.123helpme.com/view.asp?id=120541 http://www.flinnsci.com/Documents/demoPDFs/Chemistry/CF10245.pdf http://www.saskschools.ca/curr_content/chem30_05/2_kinetics/labs/clock_rxn.htm http://chemmovies.unl.edu/chemistry/dochem/DoChem114.html

Practical 2.10 Factors that influence the rate of chemical reactions Each group of students will need: Eye protection 3x Boiling tubes and a rack 10 cm3 measuring cylinder spatula Manganese(IV) oxide HARMFUL Lead(IV) oxide TOXIC Copper(II) oxide HARMFUL 20 vol H2O2 IRRITANT Washing-up liquid