Porque is used as a conjunction to express cause. It is a conjunction. 

Example:

  • I didn’t come by car because/porque I want to save fuel. 
  • We are happy because/porque you came back. 

This conjunction is equivalent to ya que, dado que or puesto que

In some cases it can be used to replace the expression para que.. 

Example:

  • I work hard so that/para que  you don’t have to. 
  • I work hard porque you don’t have/tengas que to do it. 

Note: it can be written in two words (por que). Subjunctive mood

Porqué: This noun is used to indicate a cause, a reason or a motive. 

Example:

  • I want to know the reason/el porqué for so much noise.
  • We need you to explain the reasons/ los porqués for your resignation. 

Note: as we observed in the previous example, this noun has a plural form and  goes together with  the definite article.

  Por que: It can function as a causal conjunction, but this structure can also be the result of the union between the preposition por and the relative pronoun que, these expressions are used to replace expressions such as por el cual and when you need to introduce a subordinate clause in the present subjunctive or imperfect subjunctive, respectively. 

Example:

  • In the following cases, that/que has a relative pronoun function.
  • We need you to find out the reasons why/por (las) que there was so much violence. 
  • We have several problems because/ por (los )que we are worried. 

Que is a relative pronoun and its form has these characteristics:

It has no accent, neither graphic nor prosodic (it is atonic), it has no gender or number (it is invariable).  When it is used with the preposition por, the feminine or masculine definite article can be placed between  por and que (por el/la que) or it can be replaced by: por el/la cual, por los cuales or por las cuales.  

Note: It is advisable to put the articles in between.

Examples:

  • There are several reasons why/ por (las) que we are unemployed.
  • My venture is the reason why/ (por (la) que I am saving money.
  • The reason why/por (la) que I traveled is my venture.

 Por que ( when que is as subordinating conjunction)

 Examples:

  • He was desperate for (por que) the doctor to deliver the results.
  • He is waiting for (por que) the professor to deliver the grades. 

The firemen were working hard por que / to keep the fire from spreading to the whole city.

As we have just seen, the expression por que is used when we use verbs that need a complement que whose introduction is achieved with the preposition por.

Subjunctive mood

Por qué: This sequence of the preposition por and the pronoun que is used in interrogative and exclamatory sentences.

Example: 

  • Why/ por qué aren’t you looking for a job? por qué/ what hard situations we’ve been through, we should celebrate!