Is the word acontecer the same in Brazilian and European Portuguese?

No

While the spelling and fundamental meaning of "acontecer" (to happen/to occur) are identical in both variants, there are differences in typical usage and pronunciation:

• Typical Usage (Aspect): The most significant difference lies in how the word is used to express ongoing actions. In Brazil, the gerund is the standard (e.g., está acontecendo). In Portugal, the construction preposition "a" + infinitive is used (e.g., está a acontecer).
• Typical Usage (Syntax): Portuguese speakers in Portugal frequently use the emphatic particle "é que" (e.g., O que é que aconteceu?) in questions, a structure less common in casual Brazilian speech.
• Pronunciation: Brazilian Portuguese tends to have more open, clear vowels. In Continental Portuguese, there is significant vowel reduction, where unstressed vowels are shortened or almost silenced, making the word sound more "closed."

Brazilian Portuguese Examples

1. O que está acontecendo? (What is happening?)
2. Coisas ruins acontecem com todo mundo. (Bad things happen to everyone.)
3. Eu não sei o que aconteceu ontem. (I don't know what happened yesterday.)
4. Isso vai acontecer logo. (This is going to happen soon.)
5. O que está acontecendo com você? (What is happening with you?)

Portuguese (Continental) Examples

1. O que é que está a acontecer? (What is it that is happening?)
2. Coisas más acontecem a toda a gente. (Bad things happen to everyone.)
3. Não sei o que é que aconteceu ontem. (I don't know what happened yesterday.)
4. Isto vai acontecer brevemente. (This is going to happen soon.)
5. O que é que está a acontecer contigo? (What is happening with you?)