module 3+5: rates of reaction Flashcards
what is the order in respect to the reactant when:
reactant concentration doubles and rate stays the same
order 0
what is the order in respect to the reactant when:
reactant concentration doubles and rate doubles
order 1
what is the order in respect to the reactant when:
reactant concentration doubles and rate quadruples
order 2
how do you calculate the overall order
find the sum of the reactant’s orders
what equation is used with orders and the rate constant
.
how do you find the units for K
rate is: mol/dm³/s
sub into an eq. and cancel out values to find thge units of k
what does this concentration-time graph show?
0 order
what does this concentration-time graph show?
1 order
how can you calculate the order of a reaction using half lives
zero order: successive half lives decrease with time
first order: half life remains constant
second order: successive half lives increase with time
what order does this rate-concentration graph show
order 0
what order does this rate-concentration graph show
first order
what order does this rate-concentration graph show
second order
what is the rate-determining step
the step that determines the rate of the reaction, the slowest step
all reactants from the rate equation will appear in the rate-determining step
what is the d-block
elements whose highest occupied energy level is a d sub-shell
what are the elements of the arrhenius equation and units
.
how does pressure influence rate of reaction
higher pressures compress gases into a smaller volume, thus increasing concentration so that collisions are at a higher frequency because there are more particles per unit area
how does surface area impact rate of reaction
grinding a solid increases the SA/V ratio, so the frequency of collisions increases as there are more surfaces for collisions to occur
how do catalysts affect reaction rate
they increase it without being used up
they may react to form an intermediate but are then regenerated they lower activation energy through providing an alternate reaction pathway
describe the Boltzmann distribution curve and how it changes with temperature and catalysts
line starts at 0 bc no molecules have 0 energy
line never again meets the x axis bc there’s no max energy
the area under the curve = total no. of particles
define homogeneous catalysts
the catalysts and reactants are in the same physical state, usually both aqueous
define heterogeneous catalysts
the catalyst and reactants are different physical states, usually where reactants are gases but the catalyst is a solid
what are economic and sustainability advantages of catalysts
- using a catalyst can mean lower temps and pressures can be used, saving energy costs
- saving energy costs means less us of fossil fuels/electricity which means less CO2 emissions
- catalysts can enable reactions to be used which have better atom economies
what is a half life
how long it takes for half of a reactant to be used up
why is it unlikely for some reactions to take place in one step
- a collision is unlikely between more than 2 species
- the stoichiometry in the rate equation doesn’t match the overall equation
define rate of reaction
the change in amount of reactant or product per unit time
what does the line on a conentration-time graph represent
rate
what parts of the equation do you use when writing a Kp equation
GASES ONLY!!!!’
how would you calculate initial rate of reaction
tangent from 0!!
moldm^-3s^-1 units!
how do you calculate rate for a rate equation
decrease/increase in a species divided by time
duh…
what mol value do you use when calculating delta H from q for a combustion reaction
the moles of FUEL
how would you calculate bond enthalpy of eg 2.5 of a diatomic substance if a mean value for the bond has been given
just multiply the bond value by 2.5!
multiply including the half!
draw the boltzmann distribution curve at a higher vs lower temperature
draw and label an energy profile diagram
would changing temperature affect either the rate or the rate constant
yes, both
and they will change in the same direction
how can initial rate be studied using a clock reaction
the time taken for a visual change to occur is measured, initial rate is then taken to be proportional to 1/t
it assumes that there is no significant change in the rate of reaction at the start compared to the time when taking the measurement and so the initial rate is an estimation when calculated this way
how do you calculate Kp (like the step by step)
- find equilibrium moles of each
- find total moles
- calculate mol fraction of each using these
- find partial pressure of each by doing mol fraction x total pressure
- sub partial pressures into Kp equation
- find Kp units
done!
why is a reaction spontaneous
TdeltaS > deltaH
so deltaG < O
what mole value do you use when calculating deltaH of solution from Q
the moles of the thing that you are specifically calculating deltaH for
between concentration-time graphs and rate-concentration graphs, which one show a line down, up, and flat
conc-time: down
rate-conc: flat/up
what is enthalpy change in terms of bond breaking and making
the energy released when forming bonds compared to the energy required when breaking bonds
what are the enthalpy changes of combustion of elements within a compound equal to
the enthalpy changes of formation of their respective compounds when the og reacts with O2
how is k calculated in a rate equation
sub in the rate values
make sure to put them to the power show in the equation
calculate the units for k
how is an equation given to calculate bond enthalpies different to a normal one
everything is in a gaseous state rather than their standard states
how can you make it so that the order concerning one reactant is zero when you’re trying to study the order of another reactant
use a large excess
