Question

When one mole of ammonia is heated to a given temperature, 50% of the compound dissociates and the following equilibrium is establised.

NH3(g) <-> 1/2N2(g) + 3/2H2(g)

(note: <-> is my sad attempt at the equilibrium symbol)

What is the total number of moles of gas present in this equilibrium mixture?

A 1.5
B 2.0
C 2.5
D 3.0

I'm thinking it's D, but I'm asking to check if it's as easy as adding everything up

As always, thanks for your help!

Answer 1

You're ok with that symbol. the - sign works a little better than the underline, like this <-> but usually I do <--> or <==> or <->.
Yes, it's as easy as adding everything BUT you must be careful what you add. The 50% dissociation means that NH3 is only 0.5 at equilibrium and the others change also. I is initial, c is change, E is equilibrium. The ICE chart method will solve a lot of chemistry problems if you get into the habit of thinking that way.
........NH3 ==> 1/2N2 + 3/2 H2
I......1mol......0.......0
C.....-0.5......0.25...0.75
E.....0.5......0.25.....0.75

Total = not D