CH2 june 2007 Flashcards
Nucleophile?
electron rich species that is attracted to a region of low electron density
Example of nucleophiles?
Cl-
OH-
Br-
ones that dont show charge
NH3
H2O
Octane used as a fuel?
C8H18 + 121/2 O2 —- 8CO2+9H2O
expression for the equilibrium constant Kp?
CO2(g) + 3H2(g) —–
CH4(g) + H20(g)
kP = pCH4 pH2O / pCO p H23
one method for the following the kinetics of this reaction?
Measure change in pressure at constant temp
using a manometer
Which of the forward and reverse activation energies are larger?
reverse reaction = larger
delta H = forward - backwards
Standard molar enthalpy change of formation?
enthalpy change when 1 mole of an element is formed from its constituent elements in their standard states under standard conditions
Which of the following about the use of a catalyst in equilibrium is correct?
C - equilibrium is reached faster with a catalyst
Example of a homogenous catalyst?
concentrated H2SO4 in the formation of an ester
yeast - bread brewing or making
chlorine free radicals in ozone depletion
Source of nitrogen used in Haber process?
78% in the air
What happens to the equilibrium yield of ammonia as temp is increased?
as temp increases, the yield of ammonia decreases - the equilibrium shifts to the left because the endothermic reaction = favoured
the total pressure increased?
as pressure increases, the position of equilibrium would shift to the right
as there are fewer gas molecules
rate of reaction as temp in increased?
the rate of reaction also increases
particles have more kinetic energy
and therefore, are able to collide and have a higher frequency of successful collisions
activation energy is decreased
Total pressure is increased?
rate of reaction increases
more effective collisions per unit time
why is a temp of 400 degrees and pressure of 200 atm chosen?
increasing pressure gives a higher yield of ammonia but there are increased costa as specialist equipment is needed so 200 atm is a compromise
catalyst is needed to lower the Ea
Catalyst used in haber process?
iron
What happens to any unreacted nitrogen and hydrogen?
recycled back into atmosphere
Ionic equation for the neutralisation of acid with alkali?
H +(aq) + OH-(aq) —- H2O (l)
Why is the enthalpy change of neutralisation using ethanoic acid different to hcl and hno3?
both monobasic acids
( 1 h atom)
both are strong
ethanoic acid - weak and polybasic
why does Hess’s law follow conservation of energy?
conservation of energy is where energy cannot be created or destroyed only transferred from one form to another
if hess’s law was not true, energy would be created from nothing
Delta HF?
products - reactants
Cracking def?
breaking down of alkenes into alkanes and alkenes using heat, pressure and catalyst
why does ethene have a lower bp than butene
butene has more VDW forces therefore more energy is needed to break forces between the,
Type of reaction taking place when ethene is formed?
elimination
Polymers if substituted alkenes?
Polystyrene
PVC
Explain using alkanes as examples homologous series?
Each successive member differs by CH2
compounds show similar chemical properties
methane
ethane
Structural isomers?
compounds with the same molecular formula but different structural formulas
e.g C4H10 + 2 methyl propane
Substitution reaction?
reaction in which there is a replacement or swapping of one species in the molecule by another
e.g nucleophilic substution
where OH is replaced by a halogen, forming a halogenoalkane
