speed of reaction

collision theory

the higher the frequency of successful collisions, the faster the reaction

catalysts

• substance that increases the rate of a reaction

• itself remains unchanged chemically and in its mass at the end of the reaction

measuring speed of reaction methods — mass loss method

measuring the amount of reactant used up per unit time

marble chips — CaCO3

why stopper not used?

• stopper prevents mass loss, thus cotton wool is used to allow carbon dioxide to escape

• cotton wool — prevent acid spray due to vigorous reaction

eqn: speed of reaction = amount of reactant used up/time taken

normally used for CO2 production

measuring speed of reaction methods — measuring the amount of product formed per unit time

eqn: amount of product formed/time taken

measuring speed of reaction

• change in mass of reacting mixture

• colour changes

• formation of precipitate

• pH changes

• temp changes

• titration to monitor change in conc.

collision theory core concept

• for reaction to occur, reactant particles need to collide

• however collisions with too little energy will not produce a reaction

• all colliding particles need a minimum amount of energy — activation energy

collision theory states for a reaction to occur between 2 particles —

• reacting particles must collide with each other

• must collide with minimum energy — activation energy

temperature

at low temp —

• particles have lower kinetic energy

• they possess energy lower than activation energy

• move slower ⇒ lower frequency of successful collisions between reactant particles

• slower rate of reaction

at high temp —

• particles have higher kinetic energy

• they possess a higher energy than the activation energy

• move faster ⇒ higher frequency of successful collisions between reactant particles

• faster rate of reaction

note: rate of reaction approx. doubles for every 10.0°C increase

total surface area

large lump —

• smaller surface area exposed to reactant particles

• lower frequency of successful collisions between reactant particles

• rate of reaction decreases

smaller lumps —

• increased surface area exposed to reactant particles

• higher frequency of successful collisions between reactant particles

• rate of reaction increases

concentration of reactant

dilute solution —

• fewer reactant particles per unit volume

• lower frequency of successful collisions between reactant particles

• rate of reaction decreases

concentrated solution —

• more reactant particles per unit volume

• higher frequency of successful collisions between reactant particles

• rate of reaction increases

pressure (significant for gaseous reactant)

lower pressure —

• fewer reactant particles per unit volume

• lower frequency of successful collisions between reactant particles

• rate of reaction decreases

higher pressure —

• more reactant particles per unit volume

• higher frequency of successful collisions between reactant particles

• rate of reaction increases

catalysts

• physical appearance may change at end of reaction but not its chemical properties

• not consumed during the reaction so the mass remains the same

• it increases the speed of reaction but not yield of reaction

• only small amount is required to catalyse a reaction

• most catalysts — transition metals or compounds of transitions metals

how does catalysts increase rate of reaction

increases rate of reaction —

• providing alternative reaction pathway of lower activation energy

• more reactant particles will have energy greater than equal to the activation energy to undergo successful collisions for a reaction to take place

answering tech:

• [CATALYST] speed up the reaction by providing alternative pathway of lower activation energy for the reaction to proceed

• more [REACTANT] particles have energy greater than or equal to the activation energy

• higher frequency of successful collisions to take place

• faster reaction rate

why are there high risk of explosion in coal mines

• fine coal dust burns more rapidly than large pieces of coal

• as the exposed surface are of coal dust is much greater

• when coal is extracted, a lot of dust is produced

• greater exposed surface area of coal dust when mixed with combustible gas

• result in higher frequency of successful collisions with oxygen molecules in the air

• spark can easily ignite the coal dust causing an explosion