How To Calculate Kp From Kc - Chemical Equilibrium

The Organic Chemistry Tutor
30 Jun 202010:51
EducationalLearning
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TLDRThe video script explains the process of calculating the equilibrium constant for partial pressure (kp) from the equilibrium concentration constant (kc) using a chemical reaction as an example. It details the formula, including the use of R (0.08206 L atm/mol K), the conversion of Celsius to Kelvin, and the calculation of delta n (the difference in the sum of coefficients of reactants and products). The script also demonstrates how to rearrange the formula to solve for kc given kp, using a different chemical reaction for illustration. The step-by-step calculations are provided, making it an informative guide for understanding chemical equilibrium constants.

Takeaways
  • 📝 The video explains how to calculate the equilibrium constant for partial pressure (kp) from the equilibrium constant for concentration (kc).
  • 🌡️ To calculate kp, use the formula: kp = kc * (RT)^Δn, where R is a constant with units of 0.08206 L*atm/mol*K.
  • 🔢 Convert Celsius to Kelvin by adding 273 to the Celsius temperature; the reaction temperature in the example is 123°C, thus 123 + 273 = 396 K.
  • 📌 Δn (delta n) represents the difference in the sum of the stoichiometric coefficients of the products and reactants in the balanced chemical equation.
  • ⚖️ The balanced chemical equation for the given reaction is CO + 3H2 ⇌ CH4 + H2O, with Δn being -2.
  • 🧮 Example calculation: For the given reaction, kp is found to be 3.31 * 10^-6 by using the provided values of kc, R, T, and Δn.
  • 🔄 To find kc from kp, rearrange the formula to kc = kp / (RT)^Δn and apply the balanced chemical equation for ammonia decomposition as NH3 ⇌ N2 + 3H2.
  • 📈 In the ammonia decomposition example, Δn is 2, and the calculated kc value is 5.676 * 10^-7.
  • 📚 Understanding the relationship between kc and kp is crucial for predicting the direction of chemical reactions at equilibrium.
  • 👨‍🏫 The video serves as an educational resource for those learning about chemical equilibrium and the calculation of equilibrium constants.
  • 🎥 The content is presented in a step-by-step manner, making it accessible for viewers to follow along and understand the concepts.
Q & A

  • What is the reaction discussed in the video?

    -The reaction discussed in the video is the reaction between gaseous carbon monoxide and hydrogen gas to produce methane (natural gas) and gaseous water or steam.

  • What is the significance of the equilibrium constant (Kc) and how is it related to Kp?

    -The equilibrium constant (Kc) represents the ratio of the concentrations of products to reactants raised to their stoichiometric coefficients at equilibrium. Kp, on the other hand, is the equilibrium constant in terms of partial pressures. Kp is related to Kc by the formula Kp = Kc * (RT)^Δn, where R is the gas constant, T is the temperature in Kelvin, and Δn is the difference in the sum of stoichiometric coefficients of the products and reactants.

  • How is the temperature converted from Celsius to Kelvin?

    -To convert the temperature from Celsius to Kelvin, you add 273.15 to the Celsius temperature. In the video, a temperature of 123 degrees Celsius is converted to 396 Kelvin by adding 123 + 273.15.

  • What is the value of R used in the calculations in the video?

    -The value of R (gas constant) used in the calculations in the video is 0.08206 liters times atm divided by moles times Kelvin, which is specific for use with gaseous reactions.

  • How do you calculate Δn (delta n)?

    -Δn (delta n) is calculated by taking the sum of the stoichiometric coefficients of the products and subtracting the sum of the stoichiometric coefficients of the reactants. In the given example, Δn is negative 2, as the sum of the coefficients for the products is 2 and for the reactants is 4.

  • What is the balanced chemical equation for the given reaction?

    -The balanced chemical equation for the given reaction is CO + 3H2 ⇌ CH4 + H2O. This indicates that one molecule of carbon monoxide and three molecules of hydrogen gas react to form one molecule of methane and one molecule of water.

  • What is the equilibrium constant for concentration (Kc) given in the video?

    -The equilibrium constant for concentration (Kc) given in the video is 3.5 times 10^-3.

  • How is the equilibrium constant for partial pressure (Kp) calculated from Kc?

    -The equilibrium constant for partial pressure (Kp) is calculated from Kc using the formula Kp = Kc * (RT)^Δn. By plugging in the given values for Kc, R, T, and Δn, the calculated Kp is 3.31 * 10^-6.

  • What is the second reaction discussed in the video and how is the equilibrium constant for concentration (Kc) calculated from Kp?

    -The second reaction discussed is the decomposition of ammonia (NH3) into nitrogen gas (N2) and hydrogen gas (H2). The equilibrium constant for concentration (Kc) is calculated from Kp using the rearranged formula Kc = Kp / (RT)^Δn. After balancing the chemical equation and calculating Δn, the Kc is found to be 5.676 * 10^-7.

  • What is the importance of balancing chemical equations in these calculations?

    -Balancing chemical equations is crucial for determining the stoichiometric coefficients, which are necessary for calculating Δn. This balance ensures accurate representation of the reaction and is a prerequisite for calculating the equilibrium constants, Kc or Kp.

  • How does the value of R change depending on the units used?

    -The value of R, the gas constant, changes depending on the units used. In the video, two different values of R are mentioned: 0.08206 L*atm/(mol*K) for calculations involving partial pressures and 8.3145 J/(mol*K) for other scenarios. The correct value of R must be used based on the units of the reaction conditions and the constants involved in the equilibrium constant expression.

Outlines
00:00
📚 Calculating Kp from Kc for a Chemical Reaction

This paragraph introduces the process of calculating the equilibrium constant for partial pressure (Kp) from the equilibrium concentration constant (Kc). It uses the reaction of carbon monoxide with hydrogen gas to form methane and water vapor as an example. The temperature for the reaction is given in Celsius and must be converted to Kelvin. The formula for Kp is explained, where R is a specific gas constant, and Δn is the difference in the sum of the coefficients of the products and reactants. The paragraph walks through the steps of balancing the chemical equation, calculating Δn, converting Celsius to Kelvin, and finally using the formula to find Kp. The example concludes with a calculation of Kp using the given Kc value and the derived values for temperature and Δn.

05:00
🔢 Determining Kc from Kp with a Balanced Chemical Equation

This paragraph explains how to calculate the equilibrium concentration constant (Kc) from the equilibrium constant for partial pressure (Kp), using the decomposition of ammonia as an example. It emphasizes the need to first balance the chemical equation, ensuring that the number of atoms of each element is the same on both sides. The concept of Δn is revisited, and the process of calculating it for this new reaction is detailed. The paragraph then describes the conversion of Celsius to Kelvin and the rearrangement of the Kp formula to solve for Kc. The final steps involve substituting the known values of Kp, R, temperature, and Δn into the formula to calculate the Kc value. The example concludes with a worked-out calculation, yielding the Kc value for the decomposition of ammonia.

10:08
🎓 Summary of Kp and Kc Calculation Methods

In this concluding paragraph, the video script recaps the methods for calculating Kp from Kc and vice versa. It highlights the importance of understanding the chemical reaction, balancing the equation, and using the correct values for temperature and Δn in the calculations. The paragraph ends by thanking the viewer for watching and provides a succinct summary of the key points covered in the video script, reinforcing the process of determining Kp and Kc for chemical reactions.

Mindmap
Keywords
💡Kp
Kp represents the equilibrium constant for partial pressures, which is a measure of the extent to which a reaction proceeds at equilibrium. In the context of the video, Kp is calculated from the given Kc (equilibrium constant for concentrations) and other parameters such as temperature and the number of moles of gas involved in the reaction. The calculation of Kp is crucial in understanding the equilibrium state of the reaction between carbon monoxide and hydrogen gas to produce methane and water, as it provides a quantitative assessment of the reaction's tendency to favor the formation of products over reactants.
💡Kc
Kc stands for the equilibrium constant based on concentrations, which is a dimensionless number that describes the equilibrium position of a chemical reaction in terms of the concentrations of the reactants and products. In the video, Kc is used as a starting point to derive Kp, the equilibrium constant in terms of partial pressures. The relationship between Kc and Kp is fundamental in chemical equilibrium calculations, as it allows for the conversion between different expressions of the equilibrium constant depending on the conditions of the reaction, such as temperature and the presence of gases.
💡Reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. In the video, the reaction discussed involves carbon monoxide and hydrogen gas forming methane and water vapor, which is a specific example of a chemical reaction. Understanding the details of this reaction, such as the reactants, products, and conditions under which it occurs, is essential for calculating the equilibrium constants Kc and Kp. The reaction is also balanced, which means the coefficients are adjusted to ensure mass conservation, a fundamental principle in chemistry.
💡Temperature
Temperature is a measure of the average kinetic energy of the particles in a system and plays a critical role in determining the rate and position of equilibrium of chemical reactions. In the video, the temperature is given in Celsius and must be converted to Kelvin for the equilibrium calculations. The temperature affects the values of the equilibrium constants Kc and Kp through the van't Hoff equation, which relates the change in equilibrium constants with temperature to the heat of reaction.
💡Equilibrium
Chemical equilibrium refers to the state in which the concentrations of reactants and products remain constant over time, as the forward and reverse reaction rates are equal. The video discusses how to calculate the equilibrium constants Kc and Kp, which are essential for predicting and understanding the position of equilibrium for a given reaction. The concept of equilibrium is central to the video's theme, as it is the basis for determining the extent of the reaction and the conditions under which the reaction will favor the formation of products.
💡Partial Pressure
Partial pressure is the pressure exerted by an individual gas in a mixture of gases and is an important concept when dealing with gaseous reactions at equilibrium. In the video, the calculation of Kp from Kc involves the use of partial pressures, which are directly related to the concentrations of the gaseous reactants and products. The understanding of partial pressures is crucial for the correct application of the ideal gas law and the calculation of equilibrium constants in reactions involving gases.
💡Ideal Gas Law
The ideal gas law is a mathematical equation that describes the behavior of an ideal gas in terms of its pressure, volume, temperature, and the number of moles of the gas. Although not explicitly mentioned in the video, the ideal gas law is fundamental to understanding the relationship between Kc and Kp, as it relates the concentration of a gas (in moles per volume) to its partial pressure (in atm). The video's discussion of converting Kc to Kp involves the use of the ideal gas law constants, which are essential for the calculations involving gases at equilibrium.
💡Delta N
Delta N, or the change in the number of moles of gas, is the difference between the sum of the coefficients of the gaseous products and the sum of the coefficients of the gaseous reactants in a balanced chemical equation. In the video, delta N is used to calculate the equilibrium constants Kc and Kp, as it affects the relationship between these constants and the reaction conditions. The calculation of delta N is crucial for determining the correct values of Kc and Kp, which in turn are necessary for predicting the behavior of the reaction at equilibrium.
💡Balancing Chemical Equations
Balancing chemical equations is the process of adjusting the coefficients in a chemical reaction so that the number of atoms of each element is the same on both sides of the equation. This is essential for ensuring that mass is conserved during the reaction. In the video, the chemical equations for the reactions discussed are balanced before calculating the equilibrium constants. The balanced equations provide the necessary coefficients for the reactants and products, which are then used to determine delta N and subsequently calculate Kc and Kp.
💡Van't Hoff Equation
The van't Hoff equation is not explicitly mentioned in the video, but it is an important principle in the context of equilibrium calculations. It relates the temperature dependence of the equilibrium constant to the enthalpy change of the reaction. While the video focuses on the calculation of Kc and Kp using the given constants and reaction conditions, the van't Hoff equation would be relevant if the discussion involved how the equilibrium constants change with temperature. Understanding this equation is crucial for predicting how equilibrium will shift with temperature changes.
💡Gas Laws
Gas laws, such as Boyle's Law, Charles's Law, and Avogadro's Law, describe the behavior of gases under various conditions of temperature and pressure. While not directly discussed in the video, gas laws are fundamental to understanding the relationship between concentration and partial pressure, which is essential for calculating Kc and Kp. The video's focus on the conversion between these two types of equilibrium constants assumes a basic understanding of how gas laws apply to the behavior of gases in chemical reactions.
Highlights

The video discusses the method to calculate the equilibrium constant for partial pressure (kp) from the equilibrium constant for concentration (kc).

The reaction example given involves gaseous carbon monoxide reacting with hydrogen gas to produce methane (natural gas) and gaseous water or steam at a temperature of 123 degrees Celsius.

The formula to calculate kp is kp = kc * r^Δn, where r is a constant with units of liters * atm / (moles * Kelvin) and Δn is the difference in the sum of coefficients of the products and reactants.

The temperature must be converted from Celsius to Kelvin, with Kelvin = Celsius + 273.

In the given example, the balanced chemical equation results in Δn being -2.

The equilibrium constant for concentration (kc) can be calculated by rearranging the formula for kp to kc = kp / (r^Δn).

Another example is provided to illustrate how to calculate kc from kp, involving the decomposition of ammonia into nitrogen gas and hydrogen gas.

For the ammonia decomposition example, the balanced chemical equation results in Δn being 2.

The Kelvin temperature for the ammonia decomposition example is 300 Kelvin, obtained by adding 273 to the Celsius temperature of 27.

The calculated kc value for the ammonia decomposition is 5.676 * 10^-7.

The video provides a step-by-step process for calculating kp and kc, demonstrating the application of chemical equilibrium principles.

The method explained is useful for understanding how changes in temperature affect the equilibrium constant in gaseous reactions.

The use of the sigma notation (Σ) is highlighted to represent the sum of coefficients in the balanced chemical equation.

The importance of saving the substance in its pure elemental form last when balancing chemical equations is emphasized.

The video demonstrates the necessity of using the correct units and constants when performing chemical calculations.

The process of balancing the chemical equation is crucial for determining the value of Δn and accurately calculating the equilibrium constants.

The video provides clear instructions on how to perform the calculations, making it accessible for learners at various levels of understanding.

Transcripts

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