R 2.2
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What is the rate of reaction and formula?
change in concentration of product/reactant per unit time delta conc./time
How to calculate RoR experimentally
changes in volume changes in mass changes in colour changes in conductivity clock reactions
What do reactions need to occur?
collision enough Ea proper geometric orientation
What is Ea?
minimum energy that colliding particles need to react
Effect of temperature in k.e and rate of reaction?
increasing temp increases average ke particles move faster and collide more often bigger fraction of molecules with enough energy
Factors that affect the RoR and why?
temperature - increase in collision frequency and proportion of particles with E>Ea concentration - increase in collision frequency (less effective than temp, since fraction is not changed) pressure (gases) - increase in collision frequency (more molecules/compressing it) surface area - more particles make contact, increase in collision frequency catalyst - lowers Ea
What do catalysts do?
increase RoR by providing an alternative pathway with a lower Ea
Describe the energy profile for an endothermic reaction.
reactants lower down than products
Describe the energy profile for an exothermic reaction.
products lower down than reactants
What is the transition state?
not the reactant or product, resembles both as only some bonds in the reactant are broken and some other bonds are formed
What is temperature?
a measure of the average k.e of molecules
Describe the Maxwell Boltzman curve.
y axis: number of molecules x axis: energy shifted to left, more particles with lower energy always starts at 0 asymptote at x axis
Maxwell Boltzmann - what is under the curve?
area under curve is total number of particles present to the right of the Ea - particles react
What is a reaction mechanism?
the sequence of elementary steps in which a reaction occurs
What is a reaction intermediate?
a temporary molecule produced in one step and subsequently consumed in the next, typically unstable
What is the rate determining step?
the slowest step of a chemical reaction that determines the rate of the overall reaction
What is a transition state?
unstable states between reactant and product is not reactant nor product - resembles both as some bonds have been broken and others formed exists for a short period of time and cannot be isolated from reaction mixture
Where is the transition state on the energy profile diagram?
highest point
Difference/similarities between transition states and intermediates. (4)
1 - transition states have high energy, intermediates lie between two high energy states 2- both are unstable and cannot be isolated (in some rare cases, intermediates can) 3 - every reaction has a transition state, intermediates only in 2+ step reactions 4 - transition state some bonds are broken others are formed, in intermediates all reactant bonds have been broken to form the product
How could you identify an intermediate species in an energy profile diagram?
low point between two peaks which are the transition states
What do features of energy profiles tell us?
peaks - how many steps dips - how many intermediates which peak is higher - has greater Ea - is the slow/rate-determining step distance between products and reactants - enthalpy change
What is the overall activation energy?
regardless of how many steps with different Ea, the overall Ea is determined by the highest peak
What is the molecularity of a reaction?
the number of reactant species reacting in an elementary step
What is unimolecular?
an elementary step where there is only one reactant