11.1.1 Expression for Kp

• What does the equilibrium constant Kp measure?

  Reactant and product ratios
• In the Kp expression, the term $p_{A}$ represents the partial pressure of substance A
• The coefficients in a balanced chemical equation are used as exponents in the Kp expression.
• For the reaction N_{2}(g) + 3H_{2}(g) \rightleftharpoons 2NH_{3}(g)</latex>, what is the correct Kp expression?

  $\frac{p_{NH_{3}}^{2}}{p_{N_{2}} \cdot p_{H_{2}}^{3}}$
• Steps to write an expression for Kp

  1️⃣ Write the balanced chemical equation

  2️⃣ Identify reactants and products

  3️⃣ Use the partial pressures and coefficients
• For the reaction $2SO_{2}(g) +$$O_{2}(g) \rightleftharpoons 2SO_{3}(g)$, the Kp expression is $\frac{p_{SO_{3}}^{2}}{p_{SO_{2}}^{2} \cdot p_{O_{2}}}$
• To calculate Kp, the first step is to write the balanced chemical equation
• Consider the reaction N_{2}(g) + 3H_{2}(g) \rightleftharpoons 2NH_{3}(g)</latex> with equilibrium partial pressures: $p_{N_{2}} =$$2$, $p_{H_{2}} =$$3$, and $p_{NH_{3}} =$$1$. What is the value of Kp?


  0.0185
• The Kp expression for the reaction $aA +$$bB \rightleftharpoons cC +$$dD$ is $Kp =$$\frac{p_{C}^{c} \cdot p_{D}^{d}}{p_{A}^{a} \cdot p_{B}^{b}}$
• What is the chemical formula for nitrogen gas?

  $N_{2}$
• The chemical formula for hydrogen gas is $H_{2}$
• The chemical formula for ammonia is $NH_{3}$.
• What is the Kp expression for the reaction $N_{2}(g) +$$3H_{2}(g) \rightleftharpoons 2NH_{3}(g)$?


  $Kp =$$\frac{p_{NH_{3}}^{2}}{p_{N_{2}} \cdot p_{H_{2}}^{3}}$
• When the partial pressures $p_{N_{2}} =$$2$, p_{H_{2}} =3</latex>, and $p_{NH_{3}} =$$1$ are substituted into the Kp expression, the calculated value of Kp is approximately 0.0185
• The equilibrium constant Kp measures the relative amounts of reactants and products at equilibrium, expressed in terms of partial pressures.
• What is the general Kp expression for a reversible reaction $aA +$$bB \rightleftharpoons cC +$$dD$?


  $Kp =$$\frac{p_{C}^{c} \cdot p_{D}^{d}}{p_{A}^{a} \cdot p_{B}^{b}}$
• In the general Kp expression, $p_{A}$, $p_{B}$, p_{C}</latex>, and $p_{D}$ represent the partial pressures of substances A, B, C, and D
• What is the Kp expression for the reaction $N_{2}(g) +$$3H_{2}(g) \rightleftharpoons 2NH_{3}(g)$?


  $Kp =$$\frac{p_{NH_{3}}^{2}}{p_{N_{2}} \cdot p_{H_{2}}^{3}}$
• When writing a Kp expression, the first step is to write the balanced chemical equation.
• Steps to calculate Kp from equilibrium partial pressures

  1️⃣ Write the balanced chemical equation

  2️⃣ Determine equilibrium partial pressures

  3️⃣ Construct the Kp expression using coefficients as exponents

  4️⃣ Substitute and calculate Kp
• The relationship between Kp and Kc is defined by the formula $Kp =$$Kc(RT)^{\Delta n}$
• What does $\Delta n$ represent in the relationship between Kp and Kc?


  Change in moles of gas
• If $\Delta n =$$0$, then Kp = Kc.
• Match the components of the Kp-Kc relationship with their descriptions:

  Kp ↔️ Equilibrium constant based on partial pressures

  Kc ↔️ Equilibrium constant based on concentrations

  R ↔️ Universal gas constant

  T ↔️ Temperature in Kelvin