What is Kp?

Kp is a special type of equilibrium constant that we use for reactions that are in the gas phase.

Illustrative background for K<sub>p</sub>Illustrative background for K<sub>p</sub> ?? "content

Kp

  • Where Kc uses concentrations, Kp uses partial pressures.
  • The two approaches are equivalent, but it’s much easier to measure the partial pressure of a gas than the concentration of the gas.
Illustrative background for How is K<sub>p</sub> defined?Illustrative background for How is K<sub>p</sub> defined? ?? "content

How is Kp defined?

  • The equation for Kp is:
    • Kp=(pD)d(pC)c(pA)a(pB)bK_p = \frac{(p_D)^d(p_C)^c}{(p_A)^a(p_B)^b}
    • Where the reaction is: aA(g) + bB(g) ⇋ cC(g) + dD(g)
  • Kp only includes species in the gaseous phase.

Properties of Kp

Much like Kc, Kp has a set of properties you need to know.

Illustrative background for Le ChatelierIllustrative background for Le Chatelier ?? "content

Le Chatelier

  • Le Chatelier’s principle applies to Kp as much as it does to any aqueous equilibria.
    • If you increase the pressure, the system will decrease the pressure by favoring the reaction that removes moles of gas.
    • If you increase the temperature, the system will decrease the temperature by favoring the reaction that is endothermic.
Illustrative background for TemperatureIllustrative background for Temperature ?? "content

Temperature

  • Just like Kc, Kp is temperature dependent.
  • It will have different values at different temperatures.
Illustrative background for CatalystsIllustrative background for Catalysts ?? "content

Catalysts

  • Catalysts increase the rate of reaction by providing an alternate reaction pathway with a lower activation energy.
    • They do not alter Kp.
Illustrative background for PressureIllustrative background for Pressure ?? "content

Pressure

  • Changing pressure does not alter Kp.

Jump to other topics

1Structure - Models of the Particulate of Matter

2Structure - Models of Bonding & Structure

3Structure - Classification of Matter

3.1The Periodic Table: Classification of Elements

3.2Periodic Trends

3.3Group 1 Alkali Metals

3.4Halogens

3.5Noble gases, group 18

3.6Functional Groups: Classification of Organic

3.7Functional Group Chemistry

3.8Alkanes

3.9Alcohols

3.10Halogenoalkanes

4Reactivity - What Drives Chemical Reaction?

5Reactivity - How Much, How Fast & How Far?

6Reactivity - The Mechanisms of Chemical Change

7Measurement, Data Processing & Analysis

Unlock your full potential with Seneca Premium

  • Unlimited access to 10,000+ open-ended exam questions

  • Mini-mock exams based on your study history

  • Unlock 800+ premium courses & e-books

Get started with Seneca Premium