Experiment2

# Experiment2 - EXPERIMENT 2 CHANGE REACTION KINETICS PURPOSE...

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1 EXPERIMENT 2 CHANGE: REACTION KINETICS PURPOSE: To understand the reaction kinetics as a part of chemical and biological change and to investigate the effects of the amount of material (concentration), temperature and catalysis on the reaction rate APPARATUS AND CHEMICALS 50, 150, 250 ml and 1 L Beakers Blue litmus paper Zinc dust 6 M HCl 30 % H 2 O 2 Hydrogen peroxide Washing detergent KI (Potassium iodide) Dried yeast Sugar (Sucrose= glucose + fructose C 12 H 22 O 11 = 2 C 6 H 12 O 6 - H 2 O) 10 ml Graduated cylinder Fermentation lock Warm water THEORETICAL BACKGROUND Reaction Kinetics In the most general sense, reaction kinetics is the study of rates of chemical reactions. Rate or speed refers to something that happens in a unit time, e.g. a car covering 100 kms in 1 hour has a speed of 100 km/h. In the same manner, for chemical reactions, the rate of reaction describes how fast the concentrations of a reactant or product changes with time.

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2 Calculation of the Reaction Rates : Lets consider the decomposition of an aqueous solution of hydrogen peroxide, H 2 O 2 . 2 2 2 2 2 H O (aqueous) 2 H O (aqueous) + O (gas) Suppose we start with 1 M* H 2 O 2 and discover that 10 seconds later the solution concentration is 0.98 M. The average rate of H 2 O 2 concentration change during this time interval is final conc. initial conc. 2 2 2 2 2 2 final initial 2 2 (H O ) (H O ) Rate of H O concentration change (time time ) (0.98 1) M Rate of H O concentration change (10 0) s 0.02 M /s - = - - = - = - The negative sign shows that H 2 O 2 is consumed during the reaction. 2 2 2 2 Rate of reaction of H O Rate of H O conc. change = - (*Molarity is a unit of concentration and 1M = 1 mol /L. It is also shown, for H 2 O 2 for example, as [H 2 O 2 ]) Consider the reaction aA bB cC dD + + where a moles of reactant A and b moles of reactant B are forming c moles of product C and d moles of product D . The rate of this reaction can be expressed as m n Rate of reaction k [A] [B] = Here, k is the rate constant . In that case it can be said that, the reaction is m th order in A and n th order in B . The overall order of the reaction is m + n. (Please note that m, n… etc. are generally small positive numbers and they do not need to be equal to a, b…etc.). There are zero order , first order, second order etc. chemical reactions. At the macroscopic level, we are interested in amounts reacted, formed, and the rates of their formation. But in order to explain what happens at the molecular or microscopic level, some other considerations must be made in the discussion of chemical reaction mechanism :
3 According to the collision theory Molecules or atoms of reactants must collide with each other in chemical reactions.

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Experiment2 - EXPERIMENT 2 CHANGE REACTION KINETICS PURPOSE...

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