chem 12 rates of reactions

rate definition

indication of how rapidly reaction happens

measurements of rate

changes in:

• moles/mass of reactant/product

• concentration of reactant/product

• pressure

• colour

• density

• electrical conductivity

• pH

reaction rate formula

amount/time = final amt - initial amount/change in time

nature of reactant

speed of reaction depends on types of reactants

• the more reactive, the faster the reaction

• the more bonds to be broken, the slower the reactant

reaction rate changes as nature of reactants change

phase considerations

fastest reactions between aq ions, then gases/liquids, solids

concentration of reactant’s effect on rate

reaction rate increases as concentration increases

temp of reactant’s effect on rate

reaction reate increases as temp increases

catalyst

increases rate without being consumed

• is consumed, then regenerated later in reaction

catalyst effect on reaction rate

presence of catalyst increases reaction rate

surface area of reactant

in heterogeneous reactions, increasing surface area increases rate

collision theory

reactions occur because reacting particles collide

concentration’s effect on collision theory

less particles interact in a more dilute situation, so chances of collision is lower. opposite is also true.

collision frequency

how often particles collide

temperature’s effect on collision theory

increases collision frequency, and number of particles with minimum required Ek

threshold energy

the minimum number of Ek for particles to have enough force to react. increasing the temperature of the reactant increases the likelihood that enough particles will have enough energy to react.

collision geometry

the orientation of particles: favourable collision geometry is necessary to produce reactions

successful collisions require both:

• favourable collision geometry

• sufficient kinetic energy

surface area’s effect on collision theory

when reactions occur between reactants in different phases, increasing the surface area allows particles to collide more effectively

gas pressure

decreasing the volume of an enclosed system compresses the gas, and provides same effect as increasing concentration

partial pressure

pressure of one gas in a mixture, can be described as concentration