2001
Q9) Hmm a bad
start. LCP ONLY relates to “position of equilibrium” ie the %conversion of
reactants into products (ie yield). LCP DOES NOT EXPLAIN RATES OF REACTION.
Rate of reaction is explained by referring to EA – the greater the proportion
of particles with E > EA the greater the rate.
Q10) Look
carefully. The second reaction is NOT equilibrium. It goes to completion
regardless of what chemicals are added. Adding sodium sulfate will not
changethe reactions (ie LCP does not apply). Also –sodium sulphate is a neutral
salt. It will not change the acidity of the solution
Q24a) Ammonia
is used as a cleaning agent and as a fertilizer (and was used as a
refrigerant). Ammonia is used to make urea/fertilizer. Ammonia is used to make
nitric acid which in turn is used to make explosives. This is picky but:
·
Nitric acid is not used IN explosives
·
Ammonia is not used IN explosives
·
Technically Ammonia is not used to make
explosives
·
Nitric acid is used to manufacture explosives
Q24c) The
most logical way to approach all Haber Q is to (once the equation and LCP etc
definitions are done) is i) high P (for high yield AND rate), but P limits, ii)
High temp for high rate (explain with EA), iii) Low temp for high yield(LCP) ,
iv) Compromise needed aided by a CATALYST (always mention!), v) Catalyst temp
monitored, vi) Then condensing, recycling, gs monitoring (3:1 and O2, CO). This
questions was asking you to go through i-iv
2002
Q14) Don’t
forget that higher temperatures decrease yield (lower conc of NH3 at
equilibrium) but increase rate (equilibrium conc reached sooner = steeper line
at thestart).
2003
Q29) This is
exactly the same as 2001 Q24c) above but you need to go i-vi including LCP and
EA et all the way. It is important to note that
·
You CANNOT answer a Haber/LCP question without
an equation. You SHOULD NOT answer any 3+ mark question without writing an
equation.
·
high pressure will NOT ‘cause an explosion in
the reaction vessel’. An explosion in the vessel would mean that a rapid
exothermic reaction initiated (an explosion). Instead high pressure can
burst/rupture the reaction vessel.
·
LCP DOES NOT explain rates of reaction
·
ALWAYS name the catalyst as iron, iron oxide or
magnetite
·
Remember that the gas stream must be monitored
for 1:3 N2:H2 ratio, O2 and CO
·
It is an EVALUTE – thus you need to conclude
with a judgement – is it important to monitor….
2005
Q27b) Decreasing
volume of the vessel increases the pressure on gases = increases concentration
of gases. Each gas conc must jump by the same PERCENTAGE. So if hydrogen conc
increases by half its value (1/2H on the pic below), then nitrogen and ammonia
must jump by half their original value.
Once the equilibrium shifts, each gas must change according
to their mole ratio in the equation Ie for every 1x change in mitogen there
will be a 2x change in ammonia and 3x change in hydrogen.
When the Q asks you to explain CHANGES you need to explain
ALL the changes ie why the initial spike of all three (increase P = increase
conc.), why did ammonia rise and N and H fall (LCP) an why did they come back
to point where their conc. does not
change (LCP, ie new equilibrium established).
2006
Q23b) Explain
means ‘give reasons’, specifically ‘give chemical reasons’ – so you must use
LCP to explain what happens to the OCl- ions, the position of equilibrium, the
OH- conc. and thus what happens to the pH
Q24a) THE
HABER PROCESS IS AN EQUILIBRIUM REACTION!!!!!!!!!!
Q24b) You
should know that Germany was sourcing their nitrates from South America. You
should note that the ammonia from the Haber process can be used to manufacture
nitrates. Thus, it is important that you mention that ammonia is a raw material
for the production of explosives and fertilizers. Also note that it did prolong
the war (but not wi it for Germany = lots of death = bad) but in the immediate
post war era the fertiizers allowed for increased nutrition and increase in
would population.
2008
Q7) This is a
strange one. But if you apply your Sherlock Holmes style multiple choice
reasoning “When you have eliminated the
impossible, whatever remains, however improbable must be the truth” We KNOW
that catalysts do not effect equilibrium so it must be B-D, but which of those
two are wrong?...
Q23) Again i)
Increasing Pressure DOES increase rate of reaction (it increases the concentration
of particles with E > EA thus leads to more successful collisions), ii) Even
if the Q only said T and P, the fact that a magnetite CATALYST is used allows
the temperature compromise – relatively low temp to keep yield acceptable while
maintaining a high rate.
2009
Q23) Don’t
forget that LCP states that if the conditions of equilibrium are changed the
reaction shifts to counteract the change AND A NEW EQUILIBRIUM IS ESTABLISHED.
Thus it is vital that you note a new equilibrium is established after each
change (ie at 8, 12 and 16 min).The change at 14mi is a increase in volume
(decrease in pressure). The drop in all their concentrations just reflects
their sudden drop in concentration. THEN the LCP applies showing a small shift
to the right before new equilibrium at 16 min.
2010
Q9) this was
an interesting Q – just like Sherlock you have to go through each possibility
and eliminate the impossible
Q18) This
linked LCP and BL acid theory – i) to increase chromate conc do you want to add
acid or base and then – which salt do you add?
2011
Q30) This
reaction was supposed to be one you have never seen before. You need to apply
your understanding of LCP and industrial chemistry (from the Haber topic) to
solve it. Some tips: i) look at each equation separately as they are separate
steps so each can be done under different conditions, ii) The first reaction,
the900oC says that it must be done at 900oC (suggesting a very high activation
energy) – so you have no choice on temperature – but what canyou do to
pressure, removal of species?, ii) This is just like Haber – don’t forget to
consider T, P and catalyst, removal? (but don’t have to know which catalyst),
iii) what is different about this reaction. What is the one thing we have to
maximise?
2012
Q16) Just
like in2005Q27b) you have to be very careful with the relative size of changes
in equilibrium graphs. These relative sizes relate to the mole ratio and thus
you can determine which species is which.
Q24) You had
to go a couple of steps deep here. i) ammonia to urea/fertilizer to greater
crop production nutrition and growth of world population. Ii) ammonia to nitric
acid to explosives – used in mining and construction industries allowing for
building projects and supplying raw materials for industries/modern world.
