Chemical Equilibrium Flashcards
What do 2 Mg atoms react with 1 O2 molecule to form?
2 molecules of magnesium oxide
Can you turn MgO back into magnesium and oxygen? What does this mean?
Very hard to turn MgO back into magnesium and oxygen
Reaction goes to completion
Do all reactions go to completion?
no
If a reaction does not go to completion what do you usually call it?
reversible
N2 + 3H2 -> 2NH3 What process is this?
Haber process
What is a reversible reaction?
a reaction takes place both in the forward and backward directions
is the Haber process reversible?
Yes, some of the ammonia formed decomposes and becomes Nitrogen and hydrogen again
What is chemical equilibrium?
a balance where the rate of the forward reaction is equal to the rate of the backward reaction
What is the conc. of ammonia at the beginning of the Haber process?
0
What happens to the conc. of ammonia as the Haber process reaction proceeds?
As the reaction proceeds, the conc. of N2 and H2 decreases and the conc. of NH3 increases.
What happens when the rate of production of NH3 equals its rate of decomposition?
When the rate of production of NH3 equals its rate of decomposition the reaction has reached equilibrium
What happens to the conc. of all species in the Haber process at equilibrium?
the conc. of all species remains constant
What is dynamic equilibrium?
Constantly “moving”
What is Le Chatelier’s Principle?
If a “stress” is applied to a system at equilibrium, the system readjusts itself to relieve the stress applied
What does the term “stress” mean in Le Chatelier’s Principle?
Stress is a change in reaction conditions:
- Conc of reactants/products
- Temp.
- Pressure
- Catalyst
What happens if we change the conditions of a reaction at equilibrium?
the reaction readjusts itself to relieve the stress
How does Le Chatelier’s Principle work with pressure?
Le Chatelier’s Principle predicts that in all gaseous reactions, an increase in pressure will favour the reaction which reduces the volume (i.e. towards the side with the smaller number of molecules
What does pressure only have an effect on?
Gaseous reactions
If there are the same number of molecules on both sides of the reaction, how will a change in pressure affect it?
a change in pressure will have no effect on the equilibrium
What happens when the temperature of the reaction is changed?
The reaction shifts itself to relieve the “stress”
2NO2(g) N2O4(g) What type of reaction is the forward reaction?
exothermic (produces heat)
What does changing the concentration of one of the reactants do?
shifts the reaction to the right (forwards) to relieve the stress
What does changing the concentration of the product do?
shifts the reaction to the left (backwards) to relieve the stress
What catalyst is in the Haber process?
Iron catalyst
Where is the Haber process used?
Product made at IFI plant in Cobh, Cork
What type of forward reaction is in the Haber process?
exothermic (deltaH = -92.4kJmol-1
What is the pressure in the Haber process?
4 molecules on left, 2 on right
Increase pressure will favour production of ammonia
Keeping pressure high is expensive
200 atmospheres most cost effective and safe
What is the temperature in the Haber process?
Forward reaction is exothermic
Lowering temp. will favour production of ammonia
Too slow at very low temps
500 degrees celsius temp
Haber process/chemical equilibrium equation
For reactions in the form: aA + bB -> cC + dD
Kc = [C]c[D}d over [A]a[B]b
What is the empirical formula?
The empirical formula gives the simplest whole number ratio of the numbers of the different atoms present in the molecule. (divide by Ar and get ratio) (molecular formula is a simple multiple of the empirical formula)
What is a mass spec.?
Used to analyse blood of race horses for drugs, identify substances
What is AAS?
Used to analyse water samples for heavy metals (Cd, Hg, Pb)
What is a GC?
Used with MS in drug testing also blood alcohol levels
What is HPLC used for?
Used to separate less volatile mixtures e.g. growth promoters in meat.
What is IR spec.used for?
Used to identify functional groups and identify drugs
What is UV spec. used for?
Quantitative used to find amount of org. subs. e.g. drugs
