- Joined
- Jan 20, 2008
- Messages
- 304
- Reaction score
- 0
- Points
- 0
- Pre-Dental
Advertisement - Members don't see this ad
Sorry it's ochem 152
highest MP?
(1) pentane
(2) 2-methyl butane
(3) butane
(4) 2,2-dimethyl propane
(5) propane
the answer is d. I thought d has the lowest mp..
from Kap reivew ch.4 Alkanes:
higher chain length, higher bp, mp, density
higher branching, lower bp, mp, density
from wiki: (2) has higher mp than (1)...didn't know this either..?? see the bold below!
The melting points of the alkanes follow a similar trend to boiling points for the same reason as outlined above. That is, (all other things being equal) the larger the molecule the higher the melting point. There is one significant difference between boiling points and melting points. Solids have more ridged and fixed structure than liquids. This rigid structure requires energy to break down. Thus the stronger better put together solid structures will require more energy to break apart. For alkanes, this can be seen from the graph above (i.e., the blue line). The odd-numbered alkanes have a lower trend in melting points than even numbered alkanes. This is because even numbered alkanes pack well in the solid phase, forming a well-organised structure, which requires more energy to break apart. The odd-number alkanes pack less well and so the "looser" organised solid packing structure requires less energy to break apart.
The melting points of branched-chain alkanes can be either higher or lower than those of the corresponding straight-chain alkanes, again depending on the ability of the alkane in question to packing well in the solid phase: This is particularly true for isoalkanes (2-methyl isomers), which often have melting points higher than those of the linear analogues.
Is the answer really 4???
highest MP?
(1) pentane
(2) 2-methyl butane
(3) butane
(4) 2,2-dimethyl propane
(5) propane
the answer is d. I thought d has the lowest mp..
from Kap reivew ch.4 Alkanes:
higher chain length, higher bp, mp, density
higher branching, lower bp, mp, density
from wiki: (2) has higher mp than (1)...didn't know this either..?? see the bold below!
The melting points of the alkanes follow a similar trend to boiling points for the same reason as outlined above. That is, (all other things being equal) the larger the molecule the higher the melting point. There is one significant difference between boiling points and melting points. Solids have more ridged and fixed structure than liquids. This rigid structure requires energy to break down. Thus the stronger better put together solid structures will require more energy to break apart. For alkanes, this can be seen from the graph above (i.e., the blue line). The odd-numbered alkanes have a lower trend in melting points than even numbered alkanes. This is because even numbered alkanes pack well in the solid phase, forming a well-organised structure, which requires more energy to break apart. The odd-number alkanes pack less well and so the "looser" organised solid packing structure requires less energy to break apart.
The melting points of branched-chain alkanes can be either higher or lower than those of the corresponding straight-chain alkanes, again depending on the ability of the alkane in question to packing well in the solid phase: This is particularly true for isoalkanes (2-methyl isomers), which often have melting points higher than those of the linear analogues.
Is the answer really 4???
Last edited:
