Reaction rates and equilibrium Flashcards
Define ‘the rate of a chemical reaction’
change in concentration of product over time
give the formula for finding the rate of a reaction
rate = change in conc/time
why is the rate of reaction fastest at the beginning?
each reactant is at its highest conc.
what happens to the ROR once one of the reactants has been completely used up?
the conc. stops changing and the rate of reaction is 0
what are the 4 factors that can change the rate of a chemical recation
conc.
temp.
use of catalyst.
surface area of solid reactants
what makes an effective collision between particles?
- the particles collide with correct orientation
- the particles have sufficient energy to overcome the Ae barier of the reaction
how does increasing the pressure of a gas affect the rate of reaction ?
same number of molecules occupy a smaller volume. gas molecules- closer togetehr- collide more freq. leading to more effective collisions in the same time
what are the two methods that can be used to determine the ROR for a reaction that produces gases ?
- monitoring the vol. of gas produced at regular time intervals using gas collection
- monitoring the loss of mass of reactants using a balance.
what is a catalyst?
provides an alternative rout e for the reaction with a lower Ae.
catalyst- not used up
- regenerated at end of R.
what else does it do?
The catalyst may react with a reactant to form an intermediate or may provide a surface on which the R. can take place
what are the two types of catalysts?
homogenous and heterogenous
what is a homogenous catalyst?
a catalyst that has the same physical state as the reactants.
explain what a homogeneous catalyst does.
it reacts with the reactants to form an intermediate. the intermediate then breaks down to give the products and regenerates to give the catalyst.
give one example of the use of homogeneous catalysts in chemistry.
making esters using a (homo.) sulfuric acid catalyst,
note: all the reactants and the catalysts are liquids
what is the initial rate?
the maximum rate of the reaction , its measured at , and gives the steepest gradient in a concentration time graph , usually at the beginning of the reaction
what is a heterogeneous catalyst?
catalysts that are in a different phase to the reactants.
what is the Boltzmann distribution ?
shows the distribution of molecular energies in a gas at constant temperature.
how does a heterogeneous catalyst work?
provides a surface for reactant molecules for adsorption on which the reaction can take place , after the reaction the product molecules leave the surface of the catalyst .
their work is more effective when the surface area is maximised
give one example of a heterogeneous catalyst and its use in industry?
catalytic converters pass gaseous reactants over a solid.
explain the haber process
where ammonia is formed in the reaction between nitrogen and hydrogen. The triple bond in nitrogen molecules requires a vast amount of energy to break so Fe is used as a heterogeneous catalyst to weaken this strong bond and to lower the activation energy.
uses for ammonia?
fertiliser, refrigerant gas
effect of increasing concentration of an aqueous reactant ?
increases number of reactant molecules in a given volume= frequent collisions= increasing the rate of the reaction
give two common investigations that can be used to monitor rate of reactions?
- Recording the volume of gas produced using a gas syringe
- using a balance to record loss of mass
give some examples of some uncommon investigations that can be used to monitor rate of reactions
- Using a colorimeter to record the change in concentration of coloured substances
- Timing how long it takes for a change to occur, e.g. recording how long it takes for a precipitate to form
- Determining the concentration of a reactant or product by titrating a sample of the reaction mixture
