Porqué / Porque/


Porqué


It is used as an equivalent to cause, motive, reason. It is written with an accent because it is a word with a stronger phonetic accent on the last syllable. It is a substantive because it is presided by an article such as el:
no comprendo el porqué de tu actitud ( I do not understand the reason of your attitude)
  or a determinat such as su: Todo tiene su porqué.( Everything has its cause)
The plural of porqué is porqués 

Porque

It is used to introduced subordinate sentences to express cause. It can be substituted by puesto que (since) or ya que (because).
No fuí a la fiesta porque no me tenia ganas. ( I did not go to the party because I did not fill like.)
No fuí a la fiesta ya que no tenia ganas.

It is also used at the start of a response to a Why - question.
 ¿Por qué no viniste?       Why didn't you come?
Porque no tenías ganas.    Because tou did not feel like it.

When the meaning is cause , it is incorrect to write it in two words.