f322 Flashcards
shape and bond angle of alkanes
4 bond pairs on the central atom
Equal repulsion between bond pairs
Tetrahedral
109.5’
shape and bond angle of alkenes
4 electron pairs on the central atom
1 double bond acts as one bond pair
3 bond pairs on the central atom
Equal repulsion between bond pairs
Trigonal planar
120’
state and explain the effect of an increasing chain length on the boiling points of the alkanes
As the chain length of alkanes increases the points of contact between molecules increases.
There are more intermolecular London forces between the molecules.
More energy is needed to break the stronger London forces between the molecules.
Boiling point increases.
state and explain the effect of an increasing branching on the boiling points of the alkanes
As the branching of alkanes increases the points of contact between molecules decreases.
There are less intermolecular London forces between the molecules.
Less energy is needed to break the weaker London forces between the molecules.
Boiling point decreases.
what are the limitations of radical substitution
Uncontrollable termination steps leading to a mixture of products
Further propagation steps of the mono-substituted product to form poly-substituted halogenoalkanes.
how does fractional distillation separate crude oil
Separation of a liquid mixture into fractions with different boiling points.
Longer chain higher boiling point (more London forces between the molecules) so separate at the bottom (hotter).
Shorter chain lower boiling point so separate at the top.
why are longer chain alkanes processed further
longer chain alkanes are more efficient fuels which are easier to burn.
how does incomplete combustion occur
Insufficient oxygen supply.
advantage/ disadvantage of fossil fuels.
Good source of energy
Non-renewable ( and crude oil takes millions of years to form)
why might biofuels replace crude oil
Renewable (biodiesel from rape seed, ethanol from sugar cane fermentation)
Less CO2 emissions during combustion
describe how the rates of hydrolysis of halogenoalkanes (chloro, bromo, iodo) could be measured
Add AgNO3(aq)
Add ethanol and heat
Time how long it takes for a precipitate to form (chloro white precipitate, bromo cream precipitate and Iodo yellow precipitate)
RX + H2O → ROH + HX
X(aq) + Ag+(aq) → AgX(s)
explain the rate of hydrolysis of the halogenoalkanes
C-I bond weakest and C-I bond needs least energy to break
Iodoalkane fastest rate of reaction
why might calculated enthalpy values differ from theoretical (standard) values using
a) mc∆T (Method 1)
1. Heat loss (when exothermic) or heat gain (when endothermic)
2. Not done under standard conditions
explain why an alkene displays stereoisomerism (and which type)
E/Z:
C=C can’t rotate
2 different groups attached to each carbon
Cis-Trans:
C=C can’t rotate
2 different groups attached to each C
2 substituent groups the same
describe the formation of a pi, π bond
Sideways double overlap of p-orbitals from two adjacent C atoms
