[ShannonC_77]

So I'm just working through some questions.

The question asks to write a balanced equation for the following pure substance dissolving in water.
1.  Hydrogen bromide gas

So, hydrogen bromide is H+Br-

however, since Br is a diatomic molecule, when it dissociates wouldn't the balanced equation have to be:

2 HBr = 2 H  + Br2 (lower two)?

In the book the answer is: HBr = H + Br.

Can anyone explain to my where I'm going wrong?

Thanks!

[Yggdrasil]

In water, certain classes of chemicals will dissociate into their component ions (for example, NaCl dissociates into Na⁺ and Cl^-).  HBr is among these as it will disociate into its component ions (H⁺ and Br^-).  Very rarely do chemicals dissociate into their elemental forms when put into water.

(also note that hydrogen is diatomic but dissociation of hydrogen from acids in water never produces H₂)

[iceman]

yup, your right 2HBr > H₂ + 2Br
 i think what the book did is simplify (divide by2) everything soo...
HBr > 1/2H₂ (which is H) + Br

[Yggdrasil]

HBr_(g) --> H⁺_(aq) + Br^-_(aq)

is the correct equation.