# rates equilibrium and pH part one

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• equilibrium pH and rate determining step
• the rate determining step
• this is the slowest step in a reaction this sets the rate of the reaction
• to start off it is best to write a balanced stoichiometric equation this will tell you all the reactants you will be working with
• this equation does not tell you about the reaction mechanism for the rate determining step to work this out we need to carry out some rate experiments
• the aim of these experiments is to work out the orders of the reactants as this information is needed to determine the rate determining step
• an example is  NO2+CO===> NO+ CO2
• from experimentation we determine that NO2 is second order and CO is zero order
• the equilibrium constant
• the equilibrium constant is called Kc
• here is an example of how to do a basic question on this
• N2042NO2
• the kc for this would be Kc=[NO2]^2/[N2O4]
• The units are worked out like so=(mols dm^3)/mols dm^3 so your units for this can be worked out by canceling giving the unit of mols dm^3
• this constant can only be calculated when a reaction is in dynamic eqaulibrium
• this can only occur in a closed system when the concentrations of the products and reactants stay the same
• the equilibrium constant is Kc= products/reactants
• for example
• the amount of moles in the equation for each reactant and product is the power of the concentration of each reactant and product
• Kc can have no units
• position of equilibrium and the equilibrium constant
• when the value for equalibrum = 1 this means that there is equilibrium halfway between the reactants and products
• if the kc is larger than one the reaction favours the products this means that the position of equilibrium is to the right
• if the kc is less than one this means that the position of equilibrium is favouring the reactants shifting equilibrium to the left
• temperature if increased will shift equilibrium in the endothermic direction
• if temperature is decreased it is shifted in the exothermic direction
• pressure has no effect on kc as the system will shift to maintain equilibrium in the system
• catalysts also don't effect equilibrium as they speed up the forward and reverse reaction equally
• the equilibrium constant Kc vs the rate constant k
• large Kc= equilibrium lies to the right so more products are produced
• large k= fast rate of reaction
• pressure and concentration have no effect on Kc
• pressure and concentration cause the value of k to change
• high temperature shifts the equilibrium in the endothermic direction
• low temperature shifts equilibrium in the exothermic direction
• temperature increases the rate of reaction increasing the value for k
• this changes Kc
• low temperature shifts equilibrium in the exothermic direction
• temperature increases the rate of reaction increasing the value for k
• Kc can be worked form a balanced equation k can only be used from experimental data
• acids
• three definitions for acids and bases
• arrhenius
• acid = H^+
• base = OH^-
• bronsted lowry (important need to know)
• Acid = a proton donor
• base= proton acceptor
• lewis
• acid = electron acceptor
• base=electron donor
• all acids have hydrogen in them
• three types of basic acids
• monobasic acids these have only one available hydrogen
• dibasic acid these have two available hydrogens
• tribasic acids have three available hydrogens
• conjugate acid base pairings
• a typical acid base reaction
• HCL+NaOH NaCl + H2O
• this reaction is reversible in the forward reaction the HCl is an acid ans the NaOH is a base
• in the reverse reaction the H2O can give away a H^+ ion to the NaCl which will accept it as such the water molecule becomes a acid and the NaCl becomes a base
• the NaCl is the conjugate base for HCl and the H2O is the conjugate acid for the NaOH
• another example
• HNO2+H2O====> H3O^+) +NO2^-
• in the forward reaction the HNO2 is the acid and the H2O is the base
• the conjugate base for HNO2 is NO2^-
• the conjugate acid for H2O is H3O ^+
• the definition for a conjugate acid base pairing is a pair of two species that transform into each other by the loss or gain of a proton
• acid reactions
• reactions with bases and alkalis
• acid + base/alkali====> salt + water
• acid and carbonate