chemical industry Flashcards
what does the rate of reaction measure
the rate of reactant→product conversion
formula for rate
rate = amount of reactant used or product made / time
use of rate equation
can be used to calculate the rate of reaction from concentrations and a known constant for a given temperature
rate equation
rate = k[A]^a [B]^b
[A] [B] = concentration of reactants
a b = orders of reactant
orders of reaction meaning
the power to which a concentration is raised to in the rate equation
zero order meaning
changes in concentration has no effect on rate
first order meaning
changes in concentration has a proportional change on the rate
e.g. if [A] doubles, rate doubles
second order meaning
changes in concentration has a squared proportional change on the rate
e.g. if [A] doubles, rate quadruples
features of rate constant - k
- only fixed at a particular temperature
- larger value of K, the faster the reaction
finding rate on a concentration time graph
rate is found by taking the gradient
zero order on a concentration time graph
\
diagonal line from top to bottom
zero order on a rate concentration graph
_
horizontal line, as changing concentration doesn’t affect rate
first order on a concentration time graph
slight curved slope doing down as time increases, eventually plateaus (not very steep)
first order on a rate concentration graph
/
straight diagonal line going up, as changing concentration changes rate equally
second order on a concentration time graph
curved slope doing down as time increases, eventually plateaus (steep)
second order on a rate concentration graph
curved line going up
changing concentration changes the rate squared
half life definition
the time it takes for half of the reactant to be used up
half life of zero order
half life decreases
half life of first order
half life is constant
half life of second order
half if increases
formula to calculate half life from rate constant
k = ln2 / half life
arrhenius equation for graphs
lnK = (-Ea/R) 1/T + lnA
arrhenius equation meaning
k = rate constant
A = arrhenius constant
e = exponential (on calculator)
Ea = activation energy
R = gas constant
T = temperature (in K)
what is the rate determining step
the slowest step in a multi-step reaction
the whole reaction rate depends on how quick the rds is
features of the rate equation
- reactants that appear in the rate equation affect the rate reaction
- these reactants (or substances derived from them) must appear in the rate determining step
what are reversible reactions
reactions that can go forward and backward
features of a reversible reaction
- dynamic equilibrium reached when rate of forward = rate of backward
- concentration of substance remains constant
- only occurs in closed systems
what affects value of Kc
only temperature
temperature affect on Kc
- changing the temperature will change equilibrium concentrations
- if temperature change causes equilibrium to shift to right, Kc will increase
- if temperature change causes equilibrium to shift left, Kc will decrease
Kc expression
[products] / [reactants]
what is Kc
the equilibrium constant
Kc expression of
2A + B <==> 2C + D
Kc = [C]^2 [D] / [A]^2 [B]
features of nitrogen
- diatomic molecule
- in group 5
- 1s2 2s2 2p3
- forms a covalent triple bond (very difficult to break and so nitrogen is an unreactive gas at room temperature)
common nitrogen molecules
- ammonia (NH3)
- ammonium (NH4+)
- nitrogen monoxide (NO)
- dinitrogen oxide (N2O)
- nitrogen dioxide (NO2)
features of ammonia
- NH3
- formed by N2 + H2
- formed in Haber process
- Nitrogen shares 3 of its valence electrons with hydrogen and a lone pair of electrons remain
- due to lone pair, ammonia can form hydrogen bonds with water so it is very stable
- ammonia can form dative covalent bonds using lone pair, e.g. to form ammonium ion
raw materials meaning
chemical companies will try and source raw materials that are cheap and widely available
