As a general rule all PhD-students at Department of Chemistry have to teach 140 hours per semester through the whole PhD unless stated otherwise in the contract.
If you are on the "5+3" programme you have to teach (3 x 280 hours) = 840 hours during your PhD.
If you are on the "4+4" programme you have to teach (4 x 280 hours) = 1120 hours during your PhD., but it depends of course of how many months of credit you have got transferred (in this calculation 12 months of credit is assumed, hence the PhD-education is exactly 4 years).
If you are on the "3+5" programme (i.e. no credit) you have to be aware if GSNS have allocated "full teaching" in your first year, where you typically also will have to follow a lot of courses yourself. We do not expect "full teaching" from students in their first year on the 3+5 programme.
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You are granted 1 semester (i.e. 140 hours) free of teaching, which most people choose to place at the end of the PhD when the thesis has to be written, but it is of course up to the student to decide.