Chemical Industry Flashcards
what is rate of reaction?
the change in the amount of reactants or products per unit time (normally per second)
What is the general equation for rate?
Rate = amount of reactant used/ product made / time
what is the rate constant - and what does it tell us
k
units vary so have to work them out
the bigger it is the faster the rate of reaction
what are orders of reaction?
- tells you how the reactant concentration affects the rate
- rate is proportional to [A]
- need order of reaction with respect to reactant
- reaction also has an overall order which is the sum of the orders of the different reactants
how do you find the order w.r.t a reactant?
look at how each reactant affects the rate one by one
if [A] changes and rate stays the same: 0 order w.r.t [A]
if [A] doubles and rate double (proportional): 1st order w.r.t [A]
if [A] double and the rate is 2^2 faster (triples is 3^2 faster): 2nd order w.r.t [A]
how does temperature affect the rate constant?
if you increase temperature you will increase the rate of reaction
- more kinetic energy
- particle speed up and are more likely to collide
- have the right activation energy to react so greater proportion will have enough energy to react
at a higher temperature the reaction will have a higher rate constant
What is half life?
The time taken for a reactant to halve in quantity.
What is the effect of adding a catalyst on the equilibrium constant?
None
What is the effect of increasing the temperature of a dynamic equilibrium on the position of equilibrium?
Will move it in the endothermic direction.
What is the effect of increasing the pressure of a dynamic equilibrium on the position of equilibrium?
It’ll move the position of equilibrium towards the side with the fewest moles of gas.
What is the effect of increasing the concentration of a reactant in a dynamic equilibrium on the position of equilibrium?
It will move to the right
What is the effect of increasing the pressure of a dynamic equilibrium on the equilibrium constant?
None
What is the effect of adding a catalyst on the position of equilibrium?
None
What is the effect of increasing the temperature of a dynamic equilibrium on the equilibrium constant?
Will increase if the forward reaction is endothermic, decrease if it’s exothermic.
What is the effect of increasing the concentration of a reactant in a dynamic equilibrium on the equilibrium constant?
None
How could you find the equilibrium concentration experimentally?
If it’s coloured, use colorimetry. If one of the sides contains an acid/alkali, use a pH meter. Then use the Kc equation to calculate its value.
How to follow the rate of reaction - experimental methods?
- pH measurement
- gas volume
- loss of mass
- colour change
- titration
Give an example of an initial rate experiment
Clock reactions
What are clock reactions?
measure how much time takes for a set amount of product to form changes as you vary concentrations of one of the reactants
has an easily observable end point - a colour change - that tells you when desired product is formed
the quicker the clock reaction finishes the faster the initial rate
what does the arrhenius equation link?
an equation that links the rate constant and activation enthalpy
arrhenius equation - as the activation energy gets bigger…..
…K gets smaller
arrhenius equation - a large Ea means….
…a slow rate
not many particles have enough energy to react
so only a few collisions will result in a reaction
arrhenius equation - as temperature rises….
…K increases
what is the rate determining step?
the slowest step in a multistep reaction
the overall rate is determined by this
how can you use the rate equation to determine the rate determining step?
if a reactant appears in the equation, it must affect the rate
- so this reactant or something made in it must be in the rate determining step
if a reactant doesn’t appear in the rate equation, then it isn’t involved in the rate determining step
Does the rate determining step need to be the first step in a mechanism?
No
what does the order w.r.t a reactant show about the rate determining step?
shows the no. of molecules of that reactant that are involved in the rate-determining step
What are the formulae for the oxides of nitrogen?
NO, N2O and NO2
Name NO
nitrogen(II) oxide or nitrogen (mon)oxide
How are oxides formed in the nitrogen cycle?
N2 and a multiple of O2
How are nitrate(III) ions formed in the nitrogen cycle?
ammonium ions + O2
What is produced when Devarda’s alloy reacts with a nitrate(V)?
NH3 gas, H2O and Al(OH)4-
How is nitrogen gas formed in the nitrogen cycle?
Nitrate(V) ions + H+ + e
What is Devarda’s alloy?
An alloy made from aluminium and copper
How are ammonium ions formed in the nitrogen cycle?
ammonia + H+
What is the appearance of NO2?
Brown gas
What is the formula of an ammonium ion?
NH4+
What is the formula of ammonia?
NH3
Describe the bonding in N2
Triple covalent bond
What is the appearance of N2O?
Colourless gas
Name N2O
Nitrogen(I) oxide or dinitrogen (mon)oxidide
How are nitrate(V) ions formed in the nitrogen cycle?
Nitrate(III) + H2O
What is the appearance of NO?
Colourless gas
Name NO2
Nitrogen(IV) oxide or nitrogen dioxide
How is ammonia formed in the nitrogen cycle?
N2 and H2 react
Which molecules and ions take part in the nitrogen cycle?
Ammonia, nitrogen, water, oxygen, hydrogen, nitrate(V), nitrate(III), ammonium
What is the test for nitrate(V) ions?
Add Devarda’s alloy and NaOH. Heat. Test for the ammonia gas released with damp red litmus paper —> blue
What is the formula of a nitrate(V) ion?
NO3-
What is the formula of nitrate(III)?
NO2-
What is the test for ammonium ions? Explain how it works
Add NaOH and heat. Ammonium ions will react with the OH- ions and release ammonia gas, which can be tested for with damp red litmus paper
What is the name of a NO3- ion?
Nitrate(V)
Devarda’s alloy ___ the nitrate(V) ions
Reduces
