Chapter 10 - Rates of Reaction Flashcards
rate of reaction is?
the change in the conc of r or p in a given time
how is rate calculated?
Change in conc/ time
- rate in moldm(^-3)s(^-1)
collision theory?
in order for a reaction to occur, 2 molecules must collide:
- with sufficient energy to overcome Ea
- w the correct orientation
factors affecting the ROR?
- temp
- pressure
- conc
- SA
- Presence of catalyst
factor: temp?
⬆temp =⬆KE of molecules
as KE ⬆, no. of successful collisions ⬆, R.O.R ⬆
factor: pressure?
- ⬆ P means molecules are closer together, more likely to collide and react w energy in excess of Ea, rate of collisions ⬆, ROR V
INCREASING THE PRESSURE ONLY INCREASES THE RATE OF GASEOUS REACTIONS
what does collisions are more freq mean?
more coliisons occur in a given period of time
factor: conc?
- ⬆ conc of a r ⬆ no. of moleculs of that paticular r
- ⬆ conc means molecules are closer together and there is a ⬆ chance of them colldiing w sufficient energy to overcome Ea
- ⬆ in the no. of successful collisons in a given period of time
- ROR ⬆
factor: SA?
⬆ sa of the r ⬆s the area over which a reaction can occur
ROR ⬆
factor: presence of a catalyst?
adding a catalyst to a rection provides an an alternate pathway w a lower Ea
- more particles have energy > or equal to the Ea of the catalysed reaction
- ⬆ successful collisons take place per unit time, so adding a catalyst ⬆ ROR
industrially, the yield of a reaction must be balanced against?
the economic feasibility
Haber Process equation?
N2(g) + 3H2 (g) (reversible reaction arrow) 2NH3 (g)
ΔH = -92
Haber Process optimum conditions?
- high pressure : L: 4 moles R: 2 moles so equil. moves to tight
- low temp: forwards reaction is exothermic so ⬇ temp will cause equi to shift to right
BUT THERE ARE SOME ISSUES WITH USING THESE CONDITIONS IN INDUSTRY
prblms with using high pressure?
- increasing pressure increases the conc of gases which increases ROR
- But, lots of energy is required to maintain these high pressures - expensive
- storing gases at such high pressure is unsafe
issues w low temp?
Decreases the ROR
what does the use of the Iron catalyst mean for the Haer Process?
Equil is established quickly at lower temp
what allows almost a 100% conversion rate in Haber Process?
unreacted reactants are recycled
At equil, the concs of r+ p are?
constant, but that does not mean they are of equal conc
what does the Equil. constant indicate?
- where the equil lies
- Ratio of reactants and products
what does the magnitude of Kc indicate?
the extent of reaction
in order to monitor the ROR we can monitor?
- conc of r/p -e.g. titration
- gas volume of product e.g. using gas syringe
- change in the mass of substances formed - e.g. using a balance to change in mass
ROR graph:?
X axis: time
y: change in (conc of e.g.)
calc the IROR from a graph?
- IROR shown at t=0
- draw tangent that is straight line to curve
when the graph plateaus of?
rate = 0