Chapter 10 Reaction Rates and Equilibrium Flashcards
what is rate of reaction
change in concentration (of reactants or products) in a given amount of time
what is the rate of reaction formula
change in concentration / time
how does rate of reaction change over time and why
the starts of very fast because there are lots of reactants so the concentration is very high however it gradually gets slower and slower because you begin to run out of the limiting reagent decreasing the concentration of reactants until the rate of reaction is 0 because the reaction has stopped due to their being no more limiting reagent
what are the three experimental methods to find rate of reaction
> use a gas syringe and measure how much gas is produced over time
use a cross and see how long it takes for a precipitate to obscure the cross
Use a pH meter to measure acidity of a solution
how can you find rate of reaction from a graph
draw a tangent to the graph at t=0 and the gradient of the tangent is the rate of reaction
what is collision theory
reactions occur when reactant particles collide with a certain minimum kinetic energy (activation energy)
what four factors can increase rate of reaction
> presence of a catalyst
bigger surface area (solid only)
higher temperature
increased concentration/pressure
what do squared brackets mean [ … ]
concentration of …
what do catalysts do
they are substances that remain chemically unchanged at end of a reaction but speed up rate of reaction by decreasing activation energy
how do catalysts decrease the activation energy of a reaction
they provide an alternative reaction pathway for breaking and making bonds with a lower Ea
what is a homogeneous catalyst
catalyst that is in the same physical state as the reactants
how do homogeneous catalysts work
they react with reactants to form an intermediate which can then break down to form product and regenerates the catalyst
why are homogeneous catalysts not normally used in industry
because you then have to process and separate them from the products
why are homogeneous catalysts not normally used in industry
because you then have to process and separate them from the products
how does a heterogeneous catalyst work
it provides a surface for which a reaction take place
what are three steps for how heterogeneous catalyst works
> reactants form weak adsorptive bonds to surface of catalyst
reaction takes place
the products from the reaction desorb off the surface
what is the boltzmann distribution
molecules in a sample which are all moving at different speeds/energies
what graph is the boltzmann distribution represented on
no of molecules of y axis
energy on x axis
curve that has steep incline then peaks before rapidly decreasing a bit then slowly declining for standard boltzmann distribution
dotted line marking activation energy
how do catalysts affect the boltzmann distribution
the catalyst decreases the activation energy required so shifts the activation energy line closer to the start increasing number of molecules with sufficient energy to react when they collide
how does increasing temperature affect the boltzmann distribution
increases the number of molecules with sufficient energy so curve increase not as rapidly peaks earlier but then decreases far more gradually
what is yield and what is it affected by
how much of a substance is produced
affected by the equilibrium and e Chatelier principle
what is rate of reaction affected by
collision theory
what is equilibrium
a state of balance where products can be produced and then reverted back into their original reactants
what is a dynamic equilibrium
reaction where the forward and backwards reaction continually occur at the same rate within a closed system
describe an equilibrium that makes a chemist happy
forward reaction is almost complete when equilibrium is established so the equilibrium favours the products/forward reaction
describe an equilibrium that makes a sad chemist
few reactants are converted into products when equilibrium is established so the equilibrium position favours the reactants/reverse reaction
what is the concentration rule for equilibriums
whether you start with reactants or products you always get the same concentration values for both
what is le Chatelier’s Principle
if a system is in equilibrium and a change is made in any of the conditions then the system responds to counteract the change as much as possible
what are three changes that shift an equilibrium
> adding/removing reactants/products
changing pressure
changing temperature
how does adding or removing reactants or products shift the equilibrium
adding a substance shifts the equilibrium away from its side
removing a substance shifts the equilibrium towards its side
how does changing pressure shift the equilibrium
increasing pressure shifts the equilibrium towards the side with the least moles of gas
decreasing pressure shifts the equilibrium towards the side with the most moles of gas
how does changing temperature shift the equilibrium
increasing temperature causes the equilibrium to favour the reaction that is endothermic
decreasing the temperature causes the equilibrium to favour the reaction that is exothermic
why do catalysts have no affect on the equilibrium
they remain chemically unchanged and lower the activation energy for both reactions
what is Kc
the equilibrium constant that is effectively a ratio of products to reactants
what is the general equations for equilibriums
aA + bB ⇌ cC + dD
what is the general Kc equation
( [C]^c x [D]^d) / ([A]^a x [B]^b)
what do different values for Kc mean
Kc = 1 then equilibrium is in the middle
Kc < 1 equilibrium favours the reactants
Kc > 1 equilibrium favours the products
what affects Kc
Amount of substances and pressure have no affect on Kc but changing temperature causes Kc to change
