Question: There is a typical construction that I do not know specially when concerning about movements, in which we use the preposition y instead of the subject?

Answer: 
The phrase *у меня есть* means possession = *я имею* (I have). Your sentence contains this phrase in the future tense *у меня будет* (I will have, I am having). The sentence should be:

> 
> После русского языка у меня будет химия (лекция по химии).
> 
> 
> 

You can use another verb to describe your action.

> 
> После (урока) русского языка я пойду на лекцию по химии.
> 
> 
> 

("Я буду на лекции" is understandable too, but sounds a bit clumsy.)
Russian prepositions can express either motion/tramsition, or state (both evidential and non-evidential).

The stumbling block is usually how to distinguish between a motion (or transition) and a state.

As prepositions, both ***на*** and ***в*** can be used to express either 'a translative/motional or 'an existential' state. 

The difference is expressed by a case ending (and a case). 

Locative (AKA 'Prepositional') is normally used with 'existential' state, while Accusative suggests motion or transition. Cf: 

***Я на химии*** (existential, Feminine Locative, non-evidential).

***Я на химию*** (motion, Feminine Accusative, non-evidential).

Suppose there is a room called 'химия' between pals of a chemistry lab. A guy willing to express his literal acts or states would use phrases like:

***Я в "химию"*** (motion, Feminine Accusative, evidential)

***Я в "химии"*** (existential, Feminine Locative, evidential)

In Russian, a possessive structure (e.g. phrases like 'I have', 'I own', etc.) is always a structure of state. Hence, it is possible to say 

***После русского языка я (буду) на лекции / на химии***

***После русского языка у меня будет химия***

***После русского языка я - на химию*** 

but not \* ***После русского языка я буду в лекцию химия.***