I realise these two diagrams are very similar, with the obvious difference one models the sequence of a certain function, whilst the other models the state throughout a function being carried out.
The differences that I have identified are as follows - probably incorrect:
- State chart is more of a logical view of any functionality, showing a wider array of deviating paths - however, saying that, sequence diagrams also have the ability to provide alternate (alt) paths, conditions, loops etc.
- A sequence diagram is aimed at one specific function, e.g. withdrawing money from your bank account, whereas a state chart can model a whole system.