Collision theory Flashcards
(23 cards)
what do all chemical reactions involve
the rearrangement of atoms that are already present, exisiting bonds are first broken and new bonds are formed
what does reaction rate depend on
the number of successful collisions between particles per unit time
what is a required for a successful collision
the reactant molecules must collide with each other, they must collide with sufficient energy to overcome activation energy and must collide with the correct orientation to break the bonds within the reactnats
what happens if reactant molecules dont collide with sufficient energy
the will rebound and move away from each other within reacting
the number of successful collisions from all collisions is dependent on
the number of particles per unit volume, the frequency of collisions, kinetic energy of particles and activation energy
how is a rate of reaction measured
using a range of different techniques to experimentally determine how fast a reaction is occuring, this is then represented on a rate versus time graph
how rate of reaction be measured involving the formation of gas
measuring the mass lost on a balance, measuring the volume of gas produced
how can rate of reaction be measured not involving a gas
rate of the production of a precipitate, colour change
how can the change in mass of reactions involving gas be measured
if the gas is produced in an open flask, cotton wol;l is usually placed over the mouth of the flask which allows for gas to escape but prevents any materials from being ejected from the flask (if the reaction is vigorous)
what is reaction rate
the speed at which a chemical reaction takes place, expressed as the change in concentration of a particular reactant or product per unit time
equation to calculate reaction rate
change in concentration of reactant or product/ time (units = M/s or M/min, etc) (gradient of the graph is reaction rate)
factors that affect rate of reaction
surface area of solid reactants, temperature, catalysts, gas pressure and concentration of reactants in solution
how does temperature affect reaction rate
increased temperature means greater reaction rate as particles have more kinetic energy = more more=more collisions and more energy which means more successful collisons as Ea is overcome more
how does concentration affect reaction rate
increasing concentration means that there are more reactant particles in a given volume which means more frequent collisons so faster reaction rate, number of particles is proportional to collisions (e.g double particles = double collisions)
how does pressure affect reaction rate
increasing pressure or decreasing volume will result in the particules being closer together, increasing the frequency of successful collisions per second
how does surface area affect reaction rate
increasing surface area increases reaction rate, more surface area exposed means that more collisions will occur per second (double S.A= double no. collisons)
catalyst
substances which speed up the rate of reaction without altering themselves or being consumed
trasition state
the max energy level in the energy profile diagram
Ea
minimum amount of energy required to go from the initial state to the transition state
how do catalysts speed up reaction rate
by providing an alternate pathway for the reaction to occur that has a lower Ea, meaning a higher proportion of particles will have the energy greater than Ea and will result in more successful collisions
homogenous catalysts
in the same physical state as the reactants and products
heterogenous catalysts
in a different physical state than reactants and products
