Unit 9 achapter11
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The document discusses factors that affect the rate of chemical reactions, including: 1) The nature and concentration of reactants - more active and concentrated reactants lead to faster reactions. 2) Surface area - greater surface area of reactants means more chances for molecular contact and a faster rate. 3) Temperature - higher temperatures increase molecular collisions and double the reaction rate with every 10K increase. 4) Catalysts - catalysts speed reactions by lowering activation energy without being used up in the reaction. Characteristics and types of catalysts are described.
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Unit 9 achapter11
- 23. NAME DETAILS Nature of reactant More active reactants give fast rate of reaction. No. of electrons present in innermost shell affects the reactivity of reactant. Elements of IA are more reactive than IIA. Neutralization reactions and decomposition reactions are very fast. Oxidation reduction reactions are slower. Ionic reactions are very fast. Concentration of reactant Reaction is due to effective collision of reactant molecule. Greater concentration of reactants more effective collision, thus rate of reaction will high. In case of reactants in gases, their concentration is increased by increasing their partial pressures. Rate of reaction is directly proportional to concentration of reactants. Sometime concentration of reactant become double and rate of reaction increases for four times.
- 25. Surface area Greater surface area, greater will be chance of contact of molecules. Greater surface area of molecules, greater will be rate of reaction. Light Light travel in the form of photons. Photons have energy depending on frequency of light. Light gives the energy to reactants to form activated complex in minimum time. Light increases the rate of reaction. Temperature Rate of reaction is proportional to no. of collision of molecules, this is called collision theorem. By increasing temperature, the no. of collisions of molecule increases. Rate of reaction increases by increase in temperature of reaction. By increasing temperature by 10K, the of reaction becomes doubled. Arrhenius equation: K = AE –Ea / RT the effect of temperature on rate of reaction.
- 26. • CHARACTERISTICS OF CATLYST • • Catalyst remains unchanged. • Catalyst is more effective when it is in finally divided powder form. • Catalyst should not affect chemical equilibrium state of reaction. • Catalyst cannot start a reaction; it only lowers the energy of activation. • Catalyst are specific in their nature. • Temperature affects the rate of catalyst. Temperature may decrease the volume of finally powdered catalyst. • Catalyst poisoning occur when any foreign particle involve in reaction. • Addition of impurity in catalyst is called poisoning of catalyst. • • It may be • – Permanent poisoning. – Temporary poisoning.
- 30. • ACTIVATION OF CATALYST • • Substance that increases the activity of catalyst is called promoter or activators or catalyst for catalyst. • • Example: • • Cu promotes activity of Ni in hydrogenation of oil. • When a substance reduces the rate of reaction then it is called inhibitor or negative catalyst. • In some reactions, products formed act as catalyst called autocatalysis. • Example: • Hydrolysis of ester gives acetic acid which act as catalyst. • Cu reacts with HNO3 acid produce HNO2 which act as catalyst.
- 31. • ENZYME CATALYSIS • Enzymes are biocatalytical proteins, which increase the rate of biochemical reactions. • The substance on which enzyme an attack is called substrate. • The point through which an enzyme attacks on substrate called active site. • Each enzyme has its own active site. • Specificity of substrate is present in enzyme. • Enzyme and substrate forms enzyme – substrate complex, which then converts into product. • The name of enzyme usually ends on “ase”. • Examples: – Urease. – Zymase. – Dehydrogenase. – Hydrolase. – Maltase. • CHARACTERISTICS OF ENZYME CATALYSIS• • Enzymes lower the energy of activation. • Enzymatic reactions has maximum rate at optimum temperature. • pH of media affects the activity of enzyme. • Using co – enzyme can increase activity of enzyme.