3.2.2 reaction rates

collision theory

for a reaction to occur successfully the articles must collide in right direction and have energy greater than or equal to activation energy

rate of reaction

how fast a reaction takes lace

rate of reaction equation

amount of reactant used or product formed over time

how to work out rate of reaction from grah

• gradient of curve at the given point

• draw a tangent if curved then calculate gradient

how does temperature affect rate of reaction

when a substance is heated thermal energy is transferred this energy is converted to kinetic energy so molecules move faster and further so more collisions with greater energy so more collisions have energy greater than that activation energy so increase rate as more succesful

how does concentration and ressure increase reaction rate

concentration increases more molecules in same volume so acked closer so collisions more likely and robability of collision occuring with energy greater than Ea more likely so rate of reaction increases

increase ressure ha same effect as packed closer together in smaller vlume

effect of surface area on rates of reaction

increasing surface area increases number of exposed particles so more frequenet and succesful collisions

catalyst

substance that increases rate of reaction without being used up by providing and alternative reaction ath with lower activation energy

benefits of catalyst

• lower energy costs as alow lower temperature and pressure to be use

• give higher atom economy

• increase sustainability as reduce energy demand from combustion of fossil fuels so lower CO2 emissions

reaction rofile for catalyst

homogeneous catalyst

same hysical state as reactant

heterogeneous catalysts

in a different hase than reactants eg hysical state

why are transition metals good catalysts

• varable oxidation states

• electrons are transferred to roduce and reactive intermediatie to seed u reaction rate

how does a catalyst work

adsorbing molecules onto an active site on the surface of the catalyst these active sites increas the roximity of molecules and weaken covalent bonds in the molecules so reaction occur more easily and rate is increased

ways to investigate reaction rates

• when roduct is gas formation measured using mass valance,start timer and measure at regular time intervals and when reading on mass stos decreasing sto timer

• if gas given off collect in gas syringe and calculate jow much you have at regular time intervals

maxwellboltzmann distirubtion

not all molecules in substance have same amunt of energy so distributed in attern called this ,numvber of moleculea against kinetic energy

boltzmann distribution grah

effect of temerature on boltzmann distribution

shifts right as greater roortion of molecules have greater kinetic energy

effect of concentration,ressure and surface area on boltzmann distribution

nothing as doesnt change energy

effect of catalyst on boltzamann

activation energy shifted left