CHAPTER 14 REGULAR HOMEWORK:
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A 100 L reaction container is charged with 0.502 mol of NOBr, which decomposes at a certain temperature** (say between 100 and 150 oC) according to the following reaction:
NOBr(g) ↔ NO(g) + 0.5Br2(g)
At equilibrium the bromine concentration is 1.53×10-3 M. Calculate Kc
**Not specifying the temperature allows for a more liberal use of random numbers.
Hint, first find the equilibrium concentration of each gas.
Consider the formation of hydrogen fluoride:
H2(g) + F2(g) ↔ 2HF(g)
If a 4.0 L nickel reaction container (glass cannot be used because it reacts with HF) filled with 0.0062 M H2 is connected to a 3.0 L container filled with 0.025 M F2. The equilibrium constant, Kp, is 7.8 x 1014 (Hint, this is a very large number, what does that imply?) Calculate the molar concentration of HF at equilibrium.
A further hint is provided after the first attempt in the feedback.
Hint, if you are using the quadratic equation you are making the problem much harder than it needs to be. The reaction essentially goes to completion. The problem reduces to a limiting reactant problem.
BONUS Suppose a 4.00 L nickel reaction container filled with 0.0093 M H2 is connected to a 3.00 L container filled with 0.096 M F2. Calculate the molar concentration of H2 at equilibrium.
A hint is provided after the first attempt in the feedback.
Hint, find the equilibrium concentration of HF and F2 (as in the above problem), then use the equilibrium expression to find the hydrogen concentration.
When you do the limiting reactant calculation you essentially use up all the limiting reactant. So, hydrogen concentration is approximately zero. But, it can’t be identically equal to zero or the Keq expression can not be correct. You will find how small it really is.
Sulfur dioxide reacts with chlorine at 227 oC:
SO2(g) +Cl2(g) ↔ SO2Cl2(g)
Kp for this reaction is 5.1 x 10-2 . Initially, 1.00 g each of SO2 and Cl2 are placed in a 1.00 L reaction vessel. After 15 minutes, the concentration of SO2Cl2 is 45.5 μg/mL. You will determine if the system has reached equilibrium. First, what is Kc ? (A μg is 10-6 g.)
Unfortunately, unless you learned the graphing technique or know how to use solver, you’ll have to use the quadratic equation. Next chapter we’ll learn a an easier method to solve this problem–the method of successive approximations.