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You are here: Home / Chemical Equilibrium / Chemical Equilibrium: Question on Equilibrium Constant, Kp

Chemical Equilibrium: Question on Equilibrium Constant, Kp

September 30, 2010 By Sean Chua 2 Comments

In the previous blogpost, we have discussed on the concepts of chemical equilibrium in a reversible reaction.

We have also discussed on the formula to determine Equilibrium Constant, Kc and Kp.

For Reversible Reactions involving Gases, we should use the following formula:

Equilibrium constant, Kp = (PC)c (PD)d / (PA)a (PB)b

Let’s apply the formula to a question that was given by my students from a local Junior College (JC).

Now, at equilibrium, reactant (X) and products (Y and Z) will be all present together.

Since the question stated that the pressure is constant (value is P) and the temperature is also constant, we can assume that the total pressure, PT of the gases at equIlibrium is P.

By stoichiometry ratio comparison of equation

X <=> Y + Z;

Since Mole of Y = Mole of Z at equilibrium, therefore

Partial Pressure of Y, PY = Partial Pressure of Z, PZ

Since equilibrium partial pressure of X, PX is 1/7 P, it means that the other 6/7 P of pressure must be shared equally among Y and Z.

Thus,

Partial pressure of Y, PY = 3/7 P

Partial pressure of Z, PZ = 3/7 P

Using the formula on Equilibrium Constant, we will have:

Kp = (PY)(PZ) / (PX)    =   (3/7 P)(3/7 P) / (1/7 P)   =   9/7 P

Answer: B

Are you learning something? 😀

Hope you do!

If you think the above information is useful to your friends, classmates or siblings, feel free to share it with them.

PS: Do leave me your thoughts in the comments section below. I would love to hear from you.

Related Articles:

  • Chemical Equilibrium: Reversible Reaction Introduction
  • Ideal Gas Law: Exam-Based Question
  • Ideal Gas Law: Exam-Based Question on pV = nRT
  • Ideal Gaw Law: Challenging Question
  • Key Definitions & Formulae in Atoms, Molecules and Stoichiometry

Sean Chua
Sean Chua
Winners Education Centre Pte. Ltd.
Many know me as the Ten Year Series book author for JC A-Level H2 Chemistry and O-Level Pure Chemistry. My 19+ years of coaching experience (since 1999) with more than 1500 students from 180+ JCs and Secondary Schools has allowed me to understand the true reasons why students are not able to perform well in Chemistry. Most importantly, my strength lies in using everyday analogies (even grandmothers can understand!) to simplify abstract concepts. Also, my teaching methodology has been designed to be fun, enjoyable and effective for my students.

If you want to have an enjoyable time learning Chemistry and being motivated to excel in Chemistry, contact me today at 9828 7357

Filed Under: Chemical Equilibrium Tagged With: Chemical Equilibrium, Chemistry MCQ, Chemistry Questions, Equilibrium Constant, Kc, Kp

Reader Interactions

Comments

  1. Anon-y-mouse says

    April 21, 2011 at 11:19 am

    Nice job explaining this out.

    Keep it up 😉

  2. maisie says

    September 22, 2012 at 11:01 pm

    Hi sir,
    the “heated at constant pressure” in the qn refers to the total equilibrium pressure and not the initial pressure?
    Thanks

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