Quand vs Lorsque

"Quand" corresponds exactly to the English word "when" in circumstances where "when" is linked to time.

Examples

Quand allez-vous?                                  When are you going?

Je te visiterai quand je serai à Lyon.       I will visit you when I am in Lyon.

Je me sentais mal quand j'ai vu ça.          I felt bad when I saw that.


"Lorsque" can be used in exactly the same way as "quand" to mean "when" except when forming a question. Thus, it would be correct to say:

Je te visiterai lorsque je serai à Lyon.       I will visit you when I am in Lyon.

Je me sentais mal lorsque j'ai vu ça.          I felt bad when I saw that.


However, it would be incorrect to say:

Lorsque allez-vous?                                  When are you going?
[My skin is crawling right now because this sounds so awful.]


One other use of "quand" corresponds to the English conjunction "whenever". An example would be:

Quand il arrive, je sort.                              Whenever he comes, I leave.

"Lorsque" does not mean "whenever" ever. Whenever you want to say whenever use "quand".


Finally, "lorsque" can mean "when" when in English "when" actually means "whereas". Here are some examples:

Il jouait au tennis lorsqu'il devait étudier.   He was playing tennis when/whereas he should have been
                                                                     studying.

Si je voyais un serpent je me fuirais            If I were to see a snake I would run away when/whereas
lorsqu'il faudra ne pas bouger.                     I should stand still.