Homework Help: Chemistry/ Dr.Bob222

Posted by Derrick on Tuesday, July 13, 2010 at 6:24pm.

DrBob222 I am beginning to understand about balancing equations well, thanks to your help, but there are still some other things, which I am having a hard time figuring out.

Complete and balance the following chemical reactions between an acid and a metal.

A) HBR + Mg ->

This is confusing for me, how do I balance this out?

There was a similar example like this in the book and it was ....

HBr + Al =

6HBr + 2Al -> 2AlBr3 + 3H2.

My questions are that how did they get "6" Hbr? Also where did the 2Al come from, For the product part, I know that the three comes from Aluminum, but why do they not add it in the first part. This is really confusing me now, I think I'm forgetting this whole balancing stuff. DrBob222 please bring me back on track.

Chemistry/ Dr.Bob222 - DrBob222, Tuesday, July 13, 2010 at 10:35pm
A) HBR + Mg ->

This is confusing for me, how do I balance this out?
First, write the products.
HBr + Mg ==> MgBr2 + H2
Next, balance with coefficients.
2HBr + Mg ==> MgBr2 + H2
Finally, check it.
I see 2 H on both sides.
I see 2 Br on both sides.
I see 1 Mg on both sides.
Good. Balanced.

There was a similar example like this in the book and it was ....

HBr + Al =
Write the produces.
HBr + Al ==> AlBr3 + H2
Balance with coefficients.
I note quickly that I need a 2HBr to balance H on the right but a 3HBr to balance Br on the right. When that happens, we know neither 3 nor 2 will work so we go with 6.
6HBr + 2Al ==> 2AlBr3 + 3H2.
Finally, check it.
I see 6 H on left and right.
I see 6 Br on left and right.
I see 2 Al on left and right.
Good. Balanced.

6HBr + 2Al -> 2AlBr3 + 3H2.

My questions are that how did they get "6" Hbr? Also where did the 2Al come from, For the product part, I know that the three comes from Aluminum, but why do they not add it in the first part. This is really confusing me now, I think I'm forgetting this whole balancing stuff. DrBob222 please bring me back on track.
The 2 for 2AlBr3 is used because that's the only way to get 6 Br atoms and that forces us to place a 2 for Al on the left.

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