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Chemistry (F322) > Alkanes > Flashcards

Flashcards in Alkanes Deck (19):
1

What is the general formula for an alkane?

CnH2n+2 (For non-cylcic alkanes).

2

What is the structure of alkenes? What is the bond angle?

Tetrahedral. 109.5 degrees.

3

Why does boiling point increase as chain length increases?

As in a longer chained alkane, there are more points of contact between molecules leading to more van der Waals' forces between the molecules.

4

Why do branched isomers have a lower boiling point than unbranched isomers?

In a branched alkane there are fewer points of contact between molecules, leading to fewer van der Waals' forces between the molecules. Also, branched molecules cannot get as close to each other as unbranched ones, again decreasing the intermolecular forces between the molecules.

5

Why can't alkanes mix with water? What can they dissolve in?

They are non polar. They can dissolve in most organic solvents.

6

When balancing combustion equations, what must you remember?

The same number of CO2 molecules as carbon atoms. Half the number of H2O molecules as hydrogen atoms.

7

What are the conditions for the halogenation of alkanes?

Must be ultraviolet light present or a temperature of about 300 degrees Celsius.

8

What is the initiation stage for chlorination of methane?

Cl-Cl ---->(UV light) 2Cl.

9

What are the two steps for the propagation stage of chlorination of methane?

1. Cl. + CH4 ----> CH3. + HCl
2. Cl2 + CH3. ----> CH3Cl + Cl.

10

What are the possible steps for the termination of chlorination of methane?

1. Cl. + Cl. ----> Cl2
2. Cl. + CH3. ----> CH3Cl
3. CH3. + CH3 ----> C2H6

11

What is isomerisation?

Isomerisation is the conversion of unbranched alkanes into branched alkanes.

12

What is reforming?

Reforming is turning aliphatic hydrocarbons into alicyclic hydrocarbons.

13

Burning hydrocarbons can increase atmospheric pollutants such as...?

Carbon monoxide - internal combustion engines.
Carbon dioxide - greenhouse effect.
Nitrogen oxides - acid rain.
Sulfur dioxide- acid rain.

14

How do catalytic converters work?

They convert CO into CO2. NOx is converted into N2. Unburnt hydrocarbons are converted to H2O and CO2.

15

Write the equation for the reaction between CO and NO in a catalytic converter?

2CO + 2NO ----> 2CO2 + N2

16

Outline the stages that take place in a catalytic converter to allow CO to react with NO?

The CO and NO are adsorbed onto the surface. This lowers the activation energy. A Chemical reaction takes place. CO2 and N2 desorbs from the surface.

17

Where do shorter chained hydrocarbons condense in a fractional column?

Shorter chained have lower boiling points therefore they condense at the top.

18

Where do longer chained hydrocarbons condense in a fractional column?

Longer chained have higher boiling points therefore they condense at the bottom.

19

Conditions for cracking?

Initially, the catalysts Al2O3 and SiO2 were used. However, in modern day industry cracking uses a zeolite catalyst at around 450 degrees Celsius.