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172 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 17
Example Problem 17-3
Calculating the Value of Equilibrium Constants
Nitrogen monoxide and bromine react to form nitrosyl bromide
according to the following equation.
2NO(g) ϩ Br 2 (g) 3 2NOBr(g)
Calculate K eq for this equilibrium using the data [NOBr]
ϭ 0.0474 mol/L, [NO] ϭ 0.312 mol/L, and [Br 2 ] ϭ 0.259 mol/L.
The equilibrium constant expression is as follows.
K eq ϭ
Substitute the known values into the equation and solve for K eq .
K eq ϭ
ϭ 0.0891
Note that K eq is less than 1, so the reactants are favored in this
equilibrium.
Practice Problems
3. The following is the chemical equation for the decomposition
of formamide.
HCONH 2 (g) 3 NH 3 (g) ϩ CO(g)
Calculate K eq using the equilibrium data [HCONH 2 ]
ϭ 0.0637 mol/L, [NH 3 ] ϭ 0.518 mol/L, and [CO]
ϭ 0.518 mol/L.
4. Hydrogen and carbon disulfide react to form methane and
hydrogen sulfide according to this equation.
4H 2 (g) ϩ CS 2 (g) 3 CH 4 (g) ϩ 2H 2 S(g)
Calculate K eq if the equilibrium concentrations are [H 2 ]
ϭ 0.205 mol/L, [CS 2 ] ϭ 0.0664 mol/L, [CH 4 ] ϭ 0.0196 mol/L,
and [H 2 S] ϭ 0.0392 mol/L.
[0.0474] 2
ᎏᎏ
[0.312] 2 [0.259]
[NOBr] 2
ᎏᎏ
[NO] 2 [Br 2 ]