chemical energetics and rate of reaction

exothermic

delta H <0

bond breaking < bond forming

energy released

temperature of surrounding rise

eg: combustion, neutralisation, respiration, metal displacement, condensation / freezing

endothermic

delta H >0

bond breaking > bond forming

energy absorbed

temperature of surrounding decrease

eg: electrolysis of water, thermal decomposition, photosynthesis, melting / boiling, dissolution

what is activation energy

activation energy, Ea, is the minimum amount fo energy the reactant particle must possess in order for a reaction to occur

how does concentration affect rate of reaction

when concentration increase, there is an increase in the number of reacting particles per unit volume. the frequency of collisions and frequency of effective collisions increase, hence rate of reaction increases

how does particle size affect rate of reaction

smaller particles increases the surface area to volume ration, hence the frequency of collisions and frequency of effective collisions increase and the rate of reaction also increases.

how does pressure of reactant affect the rate of reaction

at higher pressure, there is an increase in the number of gaseous particles per unit volume. frequency of colisions and frequency of effective collisions increase, hence rate of reaction also increases.

how does temperature affect rate of reaction

at higher temperatures, the particles have more kinetic energy and move faster. this increases the frequency of collisions and frequency of effective collisions increases. the particles also have energy equal to or more than the activation energy. hence, rate of reaction increases

definition of catalysts

catalusts are substances that increases the speed of a chemical reaction by providing an alternative pathway with lower activation energy. catalysts also remain chemically unchanged