r vs.h? when does it sound like an R? when does it sound like an H?
In portugues, the R sometimes sounds like and R and other times it sounds like an H. For instance, in the word for prayer: oração, it sounds like an R, and you roll it. However, in the word for repent: arrepender-se, it sounds like an H. Both examples are in the beginning of the word and between vowels. When is an R an R and when is it an H? (phonetically speaking)

Question

Answer

1) These ones sounds like the "H" sound in the English word "hall":

- "R" in the beggining of the word. 
Examples: rato, rua, rei

- "R" after "n" or "s". 
Examples: honra, Israel, genro

- "RR" (double R).
Examples: barra, carrossel, jarra

2) These ones sounds like the "R" sound, that one similar to the Spanish "R"

- "R" (single R) when is between vowels.
Examples: caro, barato, farinha

- "R" in the end of the word.
Examples: cantar, falar, comer

- "R" between a consonant and a vowel.
Examples: livre, obrigado, vidro

Answer

I'm afraid the first part of my answer  got lost in cyberspace, here's the whole thing:

There are some regional variations, but generally "r" is pronounced "h" at the beginning of a word, at the end of a syllable, or when written double ("rr"). Otherwise, it is pronounced as a flap (like in US English, the "t's" in Betty bought a bit of bitter butter.
At the end of a word, it's pronounced "h" (since it's syllable-final) except that if the next word begins with a vowel, it's usually linked to the next word as the flapped "r" (ie, single "r" between vowels). In some places (maybe Rio de Janeiro) the "r" at the end of the infinitive is especially weak, and may sound like "h" even if the next word begins in a vowel.

Note that in São Paolo (a huge city) and environs, syllable-final "r" sounds the same as in US English.  There are also places in Brazil where, instead of an "h" sound, a Spanish double r or French r is used (typical in European Portugues, btw).

Answer

Sound like "H" 
beginnig word = rato, roubo, etc
middle word
   double "rr" = agarrado, amarrado, etc
    n before r "nr" = honra, tenro, etc

Sounds like "R"
always in middle word, and single "r"

Answer

R sound
- between vowels:
Caro, Uruguay, oração, carinho

- "clusters" with b,c,d,f,g,p,t,v
Brasil, sombra, cru, lacraia, drenar, vidro, 
fragância, cifrão, grato, magro, prático, 
soprar, treino, outro, livre

H sound (all other situations)

- Roma, reto, rígido, rasteiro
- cantar, clamor, redigir
- arrepender, carro, correto
- genro, enredo, enrolado
- Israel, desregrado
- partida, cortiça, arte, sorte, morto

Answer

when written double ("rr"). Otherwise, it is pronounced as a flap (like in US English, the "t's" in Betty bought a bit of bitter butter.
At the end of a word, it's pronounced "h" (since it's syllable-final) except that if the next word begins with a vowel, it's usually linked to the next word as the flapped "r" (ie, single "r" between vowels). In some places (maybe Rio de Janeiro) the "r" at the end of the infinitive is especially weak, and may sound like "h" even if the next word begins in a vowel.

Note that in São Paolo (a huge city) and environs, syllable-final "r" sounds the same as in US English.  There are also places in Brazil where, instead of an "h" sound, a Spanish double r or French r is used (typical in European Portugues, btw).