Rates + Equilibrium Flashcards
rate equation
r = K[A][B] etc.
zero order
concentration have no effect on the rate
first order
rate increases by same factor as concentration increases
second order
rate increases by conc increase factor²
rate units
mol/dm3/s
half life
Time taken for half the reagent to be used up
half life in first order reaction
always the same
use of half lives
to determine whether or not a reaction is first order
Arrhenius equation shows
effect of changing temp/activation energy on the rate constant
Kc equation
Kc = [products] / [reactants]
mole fraction equation
= moles of gas A \ total moles of gas
partial pressure
the pressure one gas would except if it was the only gas in the container
partial pressure equation
pp = mol frac. x total pressure
only factor that changes Kc
temperature
dynamic equilibrium
both the foward and backwards reactions are taking place, at the same rate
dynamic equilibrium
both the forwards and backwards reactions are taking place, at the same rate
effect of pressure on position of equilibrium
pressure increase = favours the side with fewer gas molecules (reducing pressure of the system)
effect of temperature on position of equilibrium
temp increase = favours endothermic reaction
effect of concentration on position of equilibrium
conc. increase = favours side with fewer moles
Kc > 1 =
equilibrium position is towards PRODUCTS
Kc < 1 =
equilibrium position is towards REACTANTS
Kc = 1 =
equilibrium is HALFWAY between products and reactants
heterogeneous catalyst
catalyst in different phase (state) to reactants
homogeneous catalyst
catalyst in the same phase (state) as reactants
how does a homogeneous catalyst work?
forms intermediate species which react to form products and reform the catalyst
how does a heterogeneous catalyst work?
reaction occurs on its surface (therefore bigger SA = faster rate)
rate
the change in the amount of reactants or production per unit of time
Ea eq.
Ea = RT (ln A- Ln K)
Arrhenius equation
K = Ae [to the power or] -(Ea/RT)
gas constant
8.31 JK-1mol-1
Kp eq.
[products partial pressure] / [reactants partial pressure]
3 stages of contact process
1) sulfur solid is melted and combusted with oxygen = sulfur dioxide
2) sulfur trioxide formed from sulfur dioxide (reversible) with vanadium catalyst (exothermic) - 450 degrees C
3) sulfur trioxide reacted with oleum + conc. sulphuric acid (v. exothermic) to make sulphuric acid
uses of H2SO4
- drug manufacture
- metal treatment
- paint
- making explosives
how do catalysts reduce damage to environment? (2)
- reactions take place at lower activation energy ∴ less fuel used, less CO2 emitted
- better atom economy - less hazardous chemicals produced
uses of hydrogen? (3)
- fuel cells
- Haber process
- hydrogenation of alkenes
dynamic equilibrium
where the rate of forwards and backwards reactions are the same IN A CLOSED SYSTEM
equation for rate constant using half lives
k = ln(2) / half life
instantaneous rate
rate when t=0
method for determining Kc experimentally
- in conical flask mix substances
- add acid catalyst
- set up another conical flask with same acid catalyst as control
- stopper both flasks
- leave for a week so they reach equilibrium
- carry out titration using NaOH
- repeat titration with control to determine amount of acid catalyst used
- analyse to determine eq amounts and concs
- use kc equation
catalyst
a species which speeds up a reaction w/o undergoing permanent change itself
le Chatiliers principle
when a change is imposed on a closed system at equilibria, the position of the equilibrium will shift to minimise the effect of the change
temp increase favours
ENDOTHERMIC
temp decrease favours
EXOTHERMIC
Kc =
[products] / [reactants]
Kc > 1 =
eq. towards PRODUCTS
Kc < 1 =
eq. towards REACTANTS
K =
rate / [A]2
methods of continuous rate monitoring (2)
- gas collection
- mass lost
K = (using t 1/2)
ln2. /t 1/2
effect of temp on Kc - (temp up =)
rate up = Kc UP
Kp =
partial pressure (products) / pp. (reactants)
conc increase favours…
side producing fewer moles
conc decrease favours
side producing more moles
if K is negative ..
towards reactants
is K is positive …
towards products
