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What are the general formulae for alkanes, and for alkenes?

Answer 1

#"Alkanes........."C_nH_(2n+2)#

#"Olefins........."C_nH_(2n)#

Alkanes are saturated molecules. Their formulae correspond to #C_nH_(2n+2)#. Try it out with methane, ethane,.....hexane. Olefins have ONE so-called #"degrees of unsaturation"# with respect to equivalent alkanes. For instance, compare the formula of ethylene and propylene, #H_2C=CH_2,# and #H_3C-CH=CH_2#, with that of their saturated precursors, #H_3C-CH_3#, and #H_3C-CH_2CH_3#. What are the #C_nH_m# formula? How many degrees of unsaturation does acetylene have?

A #"degree of unsaturation"# corresponds to the presence of an olefinic bond, #HC=CH#, OR a ring junction (the ring junction reduces the overall hydrogen count by 2). Halogens count for 1 hydrogen, oxygens we ignore (though a carbonyl bond could be the source of unsaturation), and if there is nitrogen present we subtract #NH# from the formula before we assess saturation.

For more details, see here. For a practical example of how we can use this idea to interrogate a formula see here.

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Answer 2

Xavier Avery

The general formula for alkanes is CnH2n+2, where "n" represents the number of carbon atoms. The general formula for alkenes is CnH2n, where "n" also represents the number of carbon atoms.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.