write short note on factors affecting the rates of chemical reactions
Answers
Answer:
Factors that influence the reaction rates of chemical reactions include the concentration of reactants, temperature, the physical state of reactants and their dispersion, the solvent, and the presence of a catalyst.
Answer:
The rate of a chemical reaction is affected by several factors like:
1) Concentration of reactants
2) Pressure
3) Temperature
4) Catalyst
5) Nature of reactants
1. concentration of reactants
Rate of a reaction is directly proportional to the concentration of reactants.
2. pressure
The partial pressure is another way of expressing the concentration for gases. The number of collisions increases with increase in the partial pressures of gases. Hence the rate of reactions involving gaseous reactants increases with increase in partial pressures. However it has no effect on reactions involving reactants in liquid or solid phases.
It is important to keep in mind that the partial pressures of reactants can be increased by increasing the pressure of overall system. However the partial pressures do not increase when an inert gas or a non reacting gas is added to the reaction mixture at constant volume.
3. temperature
The average kinetic energy increases with increase in absolute temperature. Hence the number of molecules with energy greater than the threshold energy also increases (see the Maxwell distribution curves shown below). As a result, the number of effective collisions between reactant molecules also increases. Therefore, usually it is observed that the rate of reaction increases with increase in temperature.
4. catalyst
Catalyst is a substance which alters the rate of a reaction without being consumed or without undergoing any chemical change during the reaction.
A catalyst increases the rate of reaction by providing a new path with lower activation energy (Ea’) for the reaction. In case of reversible reactions, the catalyst lowers the activation energies of both forward and backward reactions to the same extent and helps in attaining the equilibrium quickly. Note that, as it is evident from the above diagram, when a catalyst increases the rate of forward reaction, it also increases the rate of backward reaction.
Some substances may decrease the rate of a reaction. These are generally referred to as negative catalysts or inhibitors. They interfere with the reaction by forming relatively stable complexes, which require more energy to breakup. Thus the speed of the reaction is reduced.
5.Nature of reactants
Rate of a reaction depends on the nature of bonding in the reactants. Usually the ionic compounds react faster than covalent compounds.
The reactions between ionic compounds in water occur very fast as they involve only exchange of ions, which were already separated in aqueous solutions during their dissolution.
E.g. AgCl is precipitated out immediately when AgNO3 solution is added to NaCl solution.
thre are some more which are not thre in syllabus